Effect of supplementing a Bacillus subtilis-based probiotic on performance, intestinal integrity, and serum antioxidant capacity and metabolites concentrations of heat-stressed growing pigs

Exposing pigs to heat stress (HS) seems to modify the intestinal microbiota which may compromise the integrity of the small intestine epithelia. Probiotics, live microorganisms, can help pigs to maintain a healthy intestinal environment. Eighty pigs (21.6 ± 3.4 kg body weight) exposed to HS or thermal neutral (TN) conditions were used to evaluate the effect of a Bacillus subtilis-based probiotic on performance, body temperature, and intestinal integrity. Treatments were: TN pigs fed a control diet without (TN-C) or with 1 × 106 CFU probiotic/g of feed (TN-P), and HS pigs fed a control without (HS-C) or with probiotic (HS-P). The control diet was formulated with wheat, soybean meal, and free amino acids (AA). Feed and water were freely available during the 21-d study. At completion, samples from duodenum, jejunum, and ileum were collected to analyze epithelial histology and tight junction protein expression; antioxidant activity, and free AA and metabolites in serum. Relative abundance of Lactobacillus, Bifidobacterium, Escherichia coli, and Bacillus in ileal content was analyzed. Ambient temperature in the TN room ranged from 19 to 25 °C, and in HS room from 30 to 38.5 °C. Intestinal temperature in HS-P pigs was lower than in HS-C pigs. Weight gain and feed intake reduced, but feed:gain and respiration rate increased in HS compared to TN pigs, regardless of diet (P < 0.01). Probiotic increased weight gain and improved feed:gain (P < 0.05) in both TN and HS pigs, but feed intake did not differ. Heat stress decreased villi height in jejunum and villi height:crypt depth in duodenum and jejunum (P < 0.05). Probiotic increased villi height in duodenum and ileum, and villi height:crypt depth in all small intestine segments (P < 0.05). Relative abundance of Lactobacillus and Bifidobacterium tended to reduce, and E. coli tended to increase (P < 0.10) in ileal content of HS-C pigs. Ileal relative abundance of Bacillus was higher (P < 0.01) in HS-P pigs than in HS-C and TN-C pigs. Cystathionine, homocysteine, hydroxylysine, α-amino-adipic acid, citrulline, α-amino-n-butyric acid, P-Ser, and taurine were higher in HS than in TN pigs (P < 0.05). These data confirm the negative effect of HS on performance, body temperature, and intestinal integrity of pigs. These data suggest that supplementing 1 × 106 CFU probiotic/g of feed based on Bacillus subtilis DSM 32540 may help to counteract the negative effects of HS on the performance and intestinal integrity of pigs.

Effects of dietary supplementation with L-arginine on the endogenous losses of amino acids in growing pigs exposed to heat stress

Exposing pigs to heat stress (HS) provokes higher death of intestinal cells, resulting in elevated endogenous intestinal losses (EIL) of amino acids (AA) and damage to intestinal epithelia. Arginine (Arg) is precursor for the synthesis of polyamines, which are involved in proliferation of intestinal cells and restoration of the intestinal epithelia. Thus the effect of adding L-Arg to diets for HS pigs on the EIL of AA was analyzed. Twelve pigs (23.1 ± 1.1 kg body weight) implanted with T-type cannulas at the end of ileum were individually housed and allowed 15-days for surgery recovery under thermoneutral (TN) conditions (22 ± 2 °C). Following, the pigs were randomly assigned to one of three treatments: TN pigs fed a semi-purified, corn starch-3% casein basal diet (TN-B); HS pigs with the basal diet (HS-B); HS pigs consuming the basal diet supplemented with 0.20% L-Arg (HS-Arg). The experiment consisted of two 9-day periods; each period included 7-days of adaptation to their respective diet, followed by a 2-day ileal digesta collection period. Digesta was collected during 12 consecutive hours each day. The pigs were fed twice a-day. Ambient temperature (AT) inside the TN and HS rooms ranged from 18.6 to 27.6 °C and from 29.5 to 40.7 °C, respectively. Body temperature followed a pattern similar to that of AT. The daily EIL of indispensable AA increased (P < 0.01) in the HS-B pigs compared to both the TN-B and the HS-Arg pigs, however, there was no EIL difference between the TN-B and the HS-Arg pigs (P > 0.05). Likewise, with the exception of serine, daily losses of endogenous dispensable AA in the HS-B pigs were higher (P < 0.01) in comparison with those of TN-B and HS-Arg pigs. In summary, HS exposure compared to TN conditions increases the loss of endogenous AA, but dietary supplementation with L-Arg helped to counteract the negative HS effect.

Effects of dietary protein content and crystalline amino acid supplementation patterns in low protein diets on intestinal bacteria and their metabolites in weaned pigs raised under Different sanitary conditions

The objective of this experiment was to investigate the effects of dietary crude protein (CP) content and crystalline amino acids (CAA) supplementation patterns in low CP (LCP) diets on intestinal bacteria and their metabolites in weaned pigs raised under clean (CSC) or unclean sanitary conditions (USC). One hundred forty-four piglets (6.35 ± 0.63 kg) were assigned to one of six treatments in a 3 × 2 factorial arrangement based on CP content and sanitary conditions in a randomized complete block design to give eight replicates with three pigs per pen over a 21-d period. Diets consisted of a high CP (HCP; 21%) and two LCP (18%) diets supplemented with 9 CAA (Lys, Met, Thr, Trp, Val, Ile, Leu, His, and Phe) or only six CAA (Lys, Met, Thr, Trp, Val, and Ile) to meet the requirements. The CSC room was washed weekly, whereas the USC room had sow manure spread in the pens from the beginning of the study and was not washed throughout the experiment. Jejunum and colon digesta were sampled on day 21. Both jejunum and colon digesta were analyzed for ammonia nitrogen, short-chain fatty acids, and biogenic amines but only colon digesta was analyzed for microbiome composition (16s rRNA sequencing on MiSeq). Data were analyzed using R software for 16S rRNA and the MIXED procedure of SAS for microbial metabolites. Sanitation, CP content, and CAA supplementation patterns did not affect the diversity of colonic bacterial composition in weaned pigs. Pigs raised under USC had greater (P < 0.05) jejunal ammonia nitrogen concentration than those raised under CSC. Pigs fed LCP diets had reduced (P < 0.05) jejunal ammonia nitrogen concentration compared to those fed the HCP diet. Interactions between sanitation and dietary CP content were observed (P < 0.05) for: (1) jejunal acetate and (2) colonic spermidine and spermine, whereby (1) acetate concentrations decreased from NCP to LCP in pigs raised under the CSC but those concentrations increased under the USC, and (2) spermidine and spermine concentrations increased in LCP diets compared to HCP diet under USC, unlike CSC which did not show any difference between HCP and LCP. In conclusion, reducing dietary CP lowered ammonia nitrogen content regardless of sanitation and increased microbial metabolites in weaned pigs raised under USC. However, LCP diets with different CAA supplementation patterns did not affect bacterial diversity in weaned pigs, regardless of the hygienic conditions where the animals were housed.

Effect of dl-methionine supplementation above requirement on performance; intestinal morphology, antioxidant activity, and gene expression; and serum concentration of amino acids in heat stressed pigs

The intestinal morphology and function can be compromised in pigs exposed to heat stress (HS), partly due to increased production of reactive-oxygen species. Because methionine (Met) functions as intracellular antioxidant, the requirement of Met may be increased in HS-pigs. The effect of dietary supplementation with dl-Met above requirement on performance, small intestine morphology, antioxidant enzymes activity, amino acid transporters expression, and serum concentration (SC) of free AA in HS-pigs was evaluated. A basal wheat-soybean meal diet was formulated to meet 100% Met requirement with the other indispensable AA exceeding at least 20% their requirement. Sixty individually housed pigs (23.0 ± 2.4 kg BW, 12 pigs per treatment) were randomly assigned to five treatments: TN100, thermal-neutral (22.7 °C) housed pigs fed the basal diet; HS100, HS120, HS140, HS160; HS-pigs (29.6 °C to 39.4 °C) fed the basal diet supplemented with dl-Met to contain 0%, 20%, 40%, and 60% dl-Met above the requirement, respectively. Pigs had free access to feed and water during the 21-d trial. Blood samples were collected on day 18 to analyze the absorptive AA-SC. The effect of ambient temperature (HS100 vs. TN100), as well as the linear and quadratic effects of increasing Met levels in the diets for HS-pigs were analyzed. The HS100 pigs gained less weight than TN100 and HS120 pigs (P < 0.01); gain:feed was also higher in HS120 pigs than in HS100 pigs (P ≤ 0.05). Feed intake of TN100 pigs was higher than that of HS-pigs fed the dl-Met supplemented diets (P < 0.05). Villi height reduced in pigs HS, but Met supplementation quadratically increased it (P < 0.05). Superoxide dismutase and catalase activities, reduced glutathione concentration, and relative expression of B0AT2 in ileum decreased (P < 0.05), but glutathione peroxidase activity increased in HS-pigs. dl-Met supplementation linearly affected catalase and glutathione peroxidase activities, as well as the relative expression of b0,+AT in jejunum (P < 0.05) of HS-pigs. The SC of Ile, Leu, Lys, Phe, and Val were higher in HS100 pigs than in TN100 pigs (P < 0.05). Graded levels of supplemental dl-Met in diets for HS-pigs linearly decreased SC of Ile, Leu, and Val (P < 0.05), tended to decrease His, Lys, and Thr (P < 0.10), and increased Met (P < 0.01). In conclusion, HS had negative effect on weight gain and intestinal morpho-physiology; however, it was ameliorated by adding 20% Met above the requirement in diets for growing pigs.

Apparent and standardised ileal amino acid digestibilities in heat‐stressed pigs fed wheat‐soybean meal diets supplemented with l‐arginine and dl‐methionine

Heat stress (HS) exposure may damage the small intestine epithelia of pigs affecting the digestibility and absorption of amino acids (AA). Arg and Met can enhance antioxidant and intestinal cell proliferation activity, thus supplementing them in diets might alleviate epithelial damage and correct the reduced AA digestibility. The effect of adding extra l-Arg and dl-Met to diets on the apparent (AID) and standardised ileal digestibility (SID) of AA was analysed in a 10-day experiment conducted with 10 ileal-cannulated HS pigs (25.3 ± 2.4 kg body weight). The pigs were divided into two treatments: Control, wheat-soybean meal diet supplemented with l-Lys, l-Thr, dl-Met and l-Trp; and control diet plus 0.20% l-Arg and 0.20% dl-Met (Arg + Met). Following an 8-day diet adaptation period, ileal digesta was continuously collected for 12 h, starting at 0700, on Days 9 and 10. All pigs were daily exposed to 29.6-36.1°C; ileal temperature was continuously monitored at 15-min intervals. Feed was provided twice a day. The ileal temperature ranged from 40.3 to 41.5°C. Daily ileal outflow of His, Ile, Leu, Phe, Thr, Ser and Tyr decreased (p < 0.05), and that of Arg, Val and Pro tended to decrease (p < 0.10) in the Arg + Met pigs. The AID of Arg, His, Met, Thr and Tyr, and the SID of His, Met, and Thr increased in pigs fed the Arg + Met diet (p < 0.05). Thr and Val had the lowest AID values whereas Arg, Met, and Lys had the highest values. Arg (r = 0.64) and Met (r = 0.84) intake were highly correlated with their AID values; Met intake was highly correlated with its SID value (r = 0.72). Valine and Arg had the lowest whereas Arg had the highest SID values. In conclusion, supplementing l-Arg and dl-Met above the requirement decreases the ileal outflow of several AA, and increases the AID and SID of some essential AA in HS pigs.

268 Effect of Functional Amino Acid Supplementation in low and Normal Birth Weight Pigs on Performance and Immune Status During Subsequent Salmonella Challenge

Functional amino acid (FAA) supplementation improves growth performance and immune status of weaned pigs. The objective was to determine the effects of birth weight and FAA supplementation in the post-weaning period on the response of pigs to a subsequent Salmonella (ST) challenge. Thirty-two low (1.09±0.11 kg; LBW) and normal birth weight (1.58±0.11 kg; NBW) pigs were assigned to a nursery feeding program for 4 wk in a 2 × 2 factorial with factors of birth weight category (LBW vs. NBW) and basal (FAA–) or supplemented FAA profile (FAA+; Thr, Met, and Trp at 120% of requirements). Pigs were then placed onto a grower diet and, after a 7-d adaptation period, were inoculated with ST (2.2 × 109 CFU/mL) and monitored for 7 d post-inoculation. Growth performance, rectal temperature, gut health, ST fecal shedding and translocation, and blood parameters were measured pre- and post-inoculation. Inoculation with ST increased rectal temperature (39.7 vs. 38.9±0.5 oC) and overall rectal temperature was higher in LBW compared with NBW pigs (39.6 vs. 39.0±0.5 oC; P&lt; 0.05). Salmonella shedding (1.8 vs. 2.3±0.1 score) and translocation to spleen (1.3 vs. 2.5±0.1 score) were less in NBW-FAA+ than NBW-FAA- pigs (P&lt; 0.05). Post-inoculation weight gain was greater in NBW-FAA+ compared with the other groups (0.57 vs. 0.45±0.03 kg/d; P&lt; 0.05). Post-inoculation haptoglobin (d 4; 1.0 vs. 0.7±0.1 g/L) and colonic myeloperoxidase (d 7; 4.3 vs. 2.5±0.6 µU/mL) were greater in LBW-FAA- pigs compared with the other groups (P&lt; 0.05). On d 4 post-inoculation, plasma superoxide dismutase was less in LBW- FAA+ than in LBW-FAA- (60.5 vs. 93.3±7.7 mU/mL; P&lt; 0.05). Reduced:oxidized glutathione at d 7 post-inoculation was greater in NBW compared with LBW pigs (2.5 vs. 1.7±0.3; P&lt; 0.05). In conclusion, negative effects of Salmonella infection are ameliorated with supplementation of FAA to a greater extent in NBW than in LBW pigs.

253 The Effect of Increasing Standardized Ileal Digestible Methionine Intake on Whole-Body Nitrogen Retention of Gilts During Late Gestation

A total of 70 gestating gilts (166±13 kg BW) were used to determine whole-body N retention when standardized ileal digestible (SID) methionine (Met) was fed at one of seven levels (n=10), ranging between 50 and 150% of estimated requirements during late gestation. The experimental diets provided excess Cys and 2.61, 3.39, 4.44, 5.22, 6.00, 7.05, and 7.83 g SID Met/d, respectively, with a feed allowance of 2.61 kg/d. Diets were fed to individual gilts for a 7-d adaptation period followed by a N balance period between gestation days 109 and 112. Contrast statements were used to determine linear and quadratic effects of the dietary inclusion level of Met. The average N intake was 70.8 g/d among treatments. Urinary N excretion decreased with increasing SID Met content, with no further change after 3.39 g/d SID Met (quadratic; P &lt; 0.0001). Fecal N excretion decreased with increasing SID Met content, with no further change after 5.22 g/d SID Met (linear and quadratic; P &lt; 0.0001 and P &lt; 0.05, respectively). Whole-body N retention increased as SID Met content increased between 2.61 and 4.44 g/d SID Met, no differences were observed between 4.44 and 7.05 g/d SID Met, with intermediate N retention for gilts fed 7.83 g/d SID Met (linear and quadratic; P &lt; 0.01 and P &lt; 0.0001). Whole-body N retention efficiency (% of intake) was greatest (60.74%) at 7.05 g/d SID Met. Whole-body N retention (g/d) was optimized at 4.04 and 4.58 g/d SID Met based on linear and quadratic broken-line linear models, respectively, for gilts during late gestation. Therefore, for whole-body protein retention, the average SID Met requirements (4.31 g/d) appear to be less versus those recommended by the NRC in late gestation (5.22 g SID Met/day), which do not take into consideration the non-protein partitioning of dietary Met.

Functional amino acid supplementation postweaning mitigates the response of normal birth weight more than for low birth weight pigs to a subsequent Salmonella challenge

Previous work has shown that dietary supplementation with key functional amino acids (FAA) improves growth performance and immune status of disease-challenged normal birth weight (NBW) pigs. It is not known whether FAA supplementation attenuates the effects of a subsequent disease challenge or whether this response is similar in low birth weight (LBW) pigs. The objective was to determine the effects of birth weight and FAA supplementation during the postweaning period in Salmonella-challenged pigs. Thirty-two LBW (1.08 ± 0.11 kg) and NBW (1.58 ± 0.11 kg) pigs were assigned to a nursery feeding program at weaning (25 d) for 31 days in a 2 × 2 factorial arrangement. Factors were birth weight category (LBW vs. NBW) and basal (FAA-) or supplemented FAA profile (FAA+; Thr, Met, and Trp at 120% of requirements). At d 31, pigs were placed onto a common grower diet and, after a 7-d adaptation period, were inoculated with Salmonella Typhimurium (ST; 2.2 × 10⁹ colony-forming units/mL) and monitored for 7-d postinoculation. Growth performance, rectal temperature, fecal score, indicators of gut health, ST shedding score in feces, intestinal ST colonization and translocation, and blood parameters of acute-phase response and antioxidant balance were measured pre- and postinoculation. Inoculation with ST increased temperature and fecal score, and the overall rectal temperature was higher in LBW compared to NBW pigs (P < 0.05). Postinoculation (d 7), reduced:oxidized glutathione was increased in NBW compared to LBW pigs (P < 0.05). Salmonella shedding and translocation to spleen were lower in NBW-FAA+ compared to NBW-FAA- pigs (P < 0.05). Postinoculation average daily gain was higher in NBW-FAA+ (P < 0.05) compared to the other groups. Postinoculation haptoglobin, superoxide dismutase, and colonic myeloperoxidase were increased in LBW-FAA- pigs (P < 0.05). Ileal alkaline phosphatase was decreased in LBW compared to NBW (P < 0.05). Overall, FAA supplementation represents a potential strategy to mitigate the effect of enteric disease challenge in NBW, but not LBW pigs.

Ileal alkaline phosphatase is upregulated following functional amino acid supplementation in Salmonella Typhimurium-challenged pigs

We recently showed that functional amino acid (FAA) supplementation improves growth performance and immune status of Salmonella Typhimurium (ST)-challenged pigs, which was further improved by a longer adaptation period. It is expected that the effects are associated with increased activity of intestinal alkaline phosphatase (IAP). The objective of this study was to evaluate the effects of FAA supplementation and adaptation period on the ileal, cecal, and colonic activity of IAP in weaned pigs challenged with ST. In experiment 1, a total of 32 mixed-sex weanling pigs were randomly assigned to dietary treatments in a 2 × 2 factorial arrangement with low (LP) or high protein (HP) content and basal (FAA-) or FAA profile (FAA+; Thr, Met, and Trp at 120% of requirements) as factors. In experiment 2, a total of 32 mixed-sex weanling pigs were randomly assigned to one of four dietary treatments, being FAA- fed throughout the experimental period (FAA-) or an FAA profile fed only in the post-inoculation (FAA + 0), for 1 wk pre- and post-inoculation (FAA + 1), or throughout the experimental period (FAA + 2). In experiments 1 and 2, after a 7- and 14-d adaptation period, respectively, pigs were inoculated with saline solution containing ST (3.3 and 2.2 × 109 CFU/mL, respectively). Plasma alkaline phosphatase was measured on days 0 and 7 post-inoculation in experiment 1, and IAP (ileum, cecum, and colon) was measured in experiments 1 and 2. Correlations among ileal IAP and serum albumin and haptoglobin, plasma superoxide dismutase (SOD), malondialdehyde (MDA), and reduced:oxidized glutathione, ileal myeloperoxidase, ST shedding and ileal colonization, and post-inoculation average daily gain, feed intake (ADFI), and gain:feed were also analyzed. In experiment 1, plasma alkaline phosphatase was decreased with ST inoculation and the overall content was increased in LP-FAA+ compared with LP-FAA- (P < 0.05). Moreover, ileal IAP was increased in FAA+ compared with FAA- pigs in both studies (P < 0.05) regardless of adaptation time (P > 0.05). IAP was positively correlated with MDA and ADFI and negatively correlated with SOD and ST shedding in experiment 1 (P < 0.05). These results demonstrate a positive effect of FAA supplementation, but not adaptation period, on ileal alkaline phosphatase activity in Salmonella-challenged pigs, which may be associated with improvements in antioxidant balance.

219 Effects of Feeding Low Protein Diets with Additional Supplementation of First Five Limiting AA on Performance and Diarrhea Incidence in Weaned Pigs

An experiment was conducted to evaluate the effect of feeding low crude protein (CP) diets and supplying 110% of the first 5 limiting AA on performance and diarrhea incidence in weaned pigs. One of 3 treatments were randomly assigned to 81 piglets (BW: 8.2 ± 1.2 kg; 9 pens/treatment; 3 pigs/pen) during 2 phases (3 wk each): a high CP (HP; 21 and 18%), a low CP (LP; 18 and 15%), or a low CP at 110% Lys, Met, Trp, Thr, Val requirements (LPAA; 18 and 15%) diet for phase 1 and 2, respectively. Pigs had ad libitum access to feed and water. Data were analyzed using PROC MIXED of SAS. During phase 1, pigs fed HP had the greatest ADG (P &lt; 0.05), but ADFI and G:F were not different among treatments. In phase 2, no effect of treatments was observed on growth performance. Overall, pigs fed LPAA had the lowest (P &lt; 0.05) ADG and G:F, and feeding LP decreased (P &lt; 0.05) G:F. The ADFI was not affected by the treatments. Only during wk 3, pigs fed LPAA increased (P &lt; 0.05) and LP tended to increase (P &lt; 0.10) frequency of diarrhea compared to HP. On d 21, no treatment effect was observed for ileal villi height, but LPAA reduced (P &lt; 0.05) and LP tended to reduce (P &lt; 0.10) crypt depth compared to HP. Diet analysis revealed that LP was deficient in Ile and non-essential AA (NEAA), and LPAA contained inadequate levels of Ile, Leu, His and NEAA, which explains why reduced pig performance was achieved with these 2 diets. In conclusion, low CP diets, even with additional supplementation of the first 5 limiting AA, if deficient in the next limiting AA, results in negative effects on performance and diarrhea incidence.

513 Late-Breaking: Effects of Dietary Protein Content and Crystalline Amino Acid Supplementation Patterns on Gut Health of Weaned Pigs Raised Under Different Sanitary Conditions

The objective of this experiment was to investigate the effects of dietary crude protein (CP) content and crystalline amino acids (CAA) supplementation patterns on the histomorphology, immune response, and microbial metabolites in weaned pigs under clean (CSC) or unclean sanitary conditions (USC). One hundred forty-four piglets (6.35 ± 0.63 kg BW) were assigned to 1 of 3 diets: a high CP (HCP; 21%) and two low CP (LCP; 18%) diets supplemented with 10 crystalline indispensable amino acids (IAA) to meet all IAA requirements or only 6 IAA (Lys, Met, Thr, Trp, Val, and Ile) to meet IAA requirements except for Leu, His, and Phe. Each treatment had 8 replicates per sanitary condition with 3 pigs per pen. The CSC room was cleaned and washed weekly, whereas the USC room remained unwashed throughout the experiment and had sow manure spread in the pens. Data were analyzed using the MIXED procedure of SAS with orthogonal contrasts. Pigs fed the LCP diets had longer (P &lt; 0.05) jejunal villi and higher villus height to crypt depth ratios than those fed the HCP diet. No significant difference is found in histomorphology between pigs fed LCP diets with different CAA supplementation patterns. Pigs raised under USC had greater (P &lt; 0.05) plasma interleukin (IL)-10 and IL-6 concentrations and reduced (P &lt; 0.05) plasma tumor necrosis factor-alpha concentration. Also, the LCP diets resulted in a greater (P &lt; 0.05) plasma IL-10 concentration. Interactions (P &lt; 0.05) between sanitation and dietary CP content were observed for goblet cell density and acetate and total volatile fatty acids contents in the jejunum. In conclusion, CAA supplementation patterns did not affect gut morphology in weaned pigs. Feeding LCP diets to weaned pigs improved gut morphology and microbial metabolites in jejunum under USC and ameliorated systemic inflammation induced by USC.

Changes in growth performance, plasma metabolite concentrations, and myogenic gene expression in growing pigs fed a methionine-restricted diet

Background: Methionine (Met) is usually the second or third limiting amino acid in swine diets and plays vital roles in promoting the growth, especially, the muscle growth of pigs. This research evaluated the effects of dietary Met restriction on the growth performance, plasma metabolite concentrations, and myogenic gene expression in growing pigs. Materials and methods: Eight genes in two families (myogenic regulatory factor family and myocyte enhancer factor 2 family) were selected for the analysis. Twenty individually penned barrows (crossbred, 23.6 ± 2.4 kg) were randomly allotted to two dietary treatments (n = 10). A diet based on corn and soybean meal (Diet 1, Met-restricted) was formulated to meet or exceed the energy and nutrient requirements, except for Met. Diet 2 (Met-adequate) was formulated by adding crystalline DL-Met to Diet 1 to meet the Met requirement. During the 4-week feeding trial, average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio (G:F) were measured. Immediately before and after the feeding trial, blood was sampled via jugular venipuncture for plasma nutrient metabolite analysis, while Longissimus dorsi muscle were sampled via aseptic biopsy for gene expression analysis. Data were analyzed with Student t-test. Results: Pigs fed the Met-restricted diet had lower ADG and G:F (P < 0.01). Plasma Met, cysteine, and taurine concentrations were lower (P < 0.05), while glycine and histidine concentrations were higher (P < 0.05), in pigs fed the Met-restricted diet. Furthermore, the pigs fed the Met-restricted diet tended to express less myogenic factor 6 (Myf6) and myocyte enhancer factor 2D (Mef2D) mRNA in longissimus dorsi muscle (P < 0.09). Conclusion: Given the fact that Myf6, assisted by Mef2D, is involved in myocyte differentiation, this study suggests that the reduced growth performance in the Met-restricted pigs may be associated with a reduced muscle cell differentiation.

Expression of proposed methionine transporters along the gastrointestinal tract of pigs and their regulation by dietary methionine sources

BACKGROUND

Given the key role of methionine (Met) in biological processes like protein translation, methylation, and antioxidant defense, inadequate Met supply can limit performance. This study investigated the effect of different dietary Met sources on the expression profile of various Met transporters along the gastrointestinal tract (GIT) of pigs.

METHODS

A total of 27 pigs received a diet supplemented with 0.21% DL-Met, 0.21% L-Met, or 0.31% DL-2-hydroxy-4-(methylthio)butanoic acid (DL-HMTBA). Changes in mRNA expression of B⁰AT1, ATB^0,+, rBAT, ASCT2, IMINO, LAT4, y⁺LAT1, LAT2, and SNAT2 were evaluated in the oral mucosa, cardia, fundus, pylorus, duodenum, proximal jejunum, middle jejunum, ileum, cecum, proximal colon, and distal colon, complemented by protein expression analysis of B⁰AT1, ASCT2, LAT2, and LAT4.

RESULTS

Expression of all investigated transcripts differed significantly along the GIT. B⁰AT1, rBAT, y⁺LAT1, LAT2, and LAT4 showed strongest mRNA expression in small intestinal segments. ASCT2, IMINO, and SNAT2 were similarly expressed along the small and large intestines but expression differed in the oral mucosa and stomach. ATB^0,+ showed highest mRNA expression in large intestinal tissues, cardia, and pylorus. In pigs fed DL-Met, mRNA expression of ASCT2 was higher than in pigs fed DL-HMTBA in small intestinal tissues and mRNA expression of IMINO was lower than in pigs fed L-Met in large intestinal tissues. Dietary DL-HMTBA induced a stronger mRNA expression of basolateral uptake systems either in the small (LAT2) or large (y⁺LAT1) intestine. Protein expression of B⁰AT1 was higher in the middle jejunum and ileum in pigs fed DL-Met when compared with the other Met supplements. LAT4 expression was higher in pigs fed DL-HMTBA when compared with DL-Met (small intestine) and L-Met (small intestine, oral mucosa, and stomach).

CONCLUSION

A high expression of several Met transporters in small intestinal segments underlines the primary role of these segments in amino acid absorption; however, some Met transporters show high transcript and protein levels also in large intestine, oral mucosa, and stomach. A diet containing DL-Met has potential to increase apical Met transport in the small intestine, whereas a diet containing DL-HMTBA has potential to increase basolateral Met transport in the small intestine and, partly, other gastrointestinal tissues.

Effects of supplemental d-methionine in comparison to l-methionine on nitrogen retention, gut morphology, antioxidant status, and mRNA abundance of amino acid transporters in weanling pigs

An N-balance experiment was conducted to test the hypothesis that d-Methionine (d-Met) has the same bioavailability and efficacy as l-Methionine (l-Met) when fed to weanling pigs. A Met-deficient basal diet containing 0.24% standardized ileal digestible (SID) Met was formulated. Six additional diets were formulated by adding 0.036%, 0.072%, or 0.108% d-Met or l-Met to the basal diet, and these diets, therefore, contained 77%, 87%, or 97% of the requirement for SID Met. Fifty-six barrows (10.53 ± 1.17 kg) were housed in metabolism crates and allotted to the seven diets with eight replicate pigs per diet. Feces and urine were collected quantitatively with 7-d adaptation and 5-d collection periods. Blood and tissue samples from pigs fed the basal diet and pigs fed diets containing 0.108% supplemental Met were collected on the last day. Results indicated that N retention (%) linearly increased (P < 0.01) as supplemental d-Met or l-Met increased in diets. Based on N retention (%) as a response, the linear slope-ratio regression estimated the bioavailability of d-Met relative to l-Met to be 101% (95% confidence interval: 57%-146%). The villus height and crypt depth in the jejunum were not affected by the Met level or Met source. Total antioxidant capacity or thiobarbituric acid reactive substance concentrations in plasma or tissue samples from pigs fed the control diet or diets containing 0.108% supplemental d-Met or l-Met were not different. Abundance of mRNA for some AA transporters analyzed in intestinal mucosa of pigs also did not differ. Therefore, it is concluded that d-Met and l-Met are equally bioavailable for weanling pigs.

Effect of arginine supplementation on the morphology and function of intestinal epithelia, and serum concentrations of amino acids in pigs exposed to heat stress

The exposure of pigs to heat stress (HS) appears to damage their intestinal epithelia, affecting the absorption of amino acids (AA). Arg is involved in the restoration of intestinal epithelial cells but HS reduces Arg intake. The effect of dietary supplementation with Arg on morphology of intestinal epithelia, AA transporter gene expression, and serum concentration (SC) of free AA in HS pigs were analyzed. Twenty pigs (25.3 ± 2.4 kg BW) were randomly assigned to two dietary treatments: control (0.81% Arg), wheat-soybean meal diet supplemented with L-Lys, L-Thr, DL-Met and L-Trp, and the experimental diet where 0.16% free L-Arg was supplemented to a similar control diet (+Arg). All pigs were individually housed and exposed to HS, fed at libitum with full access to water. The ambient temperature, recorded at 15-min intervals during the 21-d trial, ranged on average from 29.6 to 39.4 °C within the same day. Blood samples were collected on d18 at 1600 h (ambient temperature peak); serum was separated by centrifugation. At the end of the trial, five pigs per treatment were sacrificed to collect samples of mucosa scratched from each small intestine segment. The expression of AA transporters in intestinal mucosa and the SC of AA were analyzed. Villi height was higher (P < 0.01) in duodenum, jejunum, and ileum but the crypt depth did not differ between the control and the +Arg pigs. Supplementation of L-Arg increased the mRNA coding for the synthesis of the cationic AA transporter b 0,+ (P < 0.01) and the neutral AA transporter B 0 (P < 0.05) in duodenum by approximately five-folds and three-folds, respectively, but no effect on mRNA abundance was observed in jejunum and ileum. The supplementation of L-Arg increased serum Arg, His, Met, Thr, Trp, and urea (P < 0.05); tended to increase Val (P < 0.10), but did not affect Ile, Lys, Leu, and Phe. These results indicate that supplementing 0.16% L-Arg to the control diet may help to improve the function of the small intestine epithelium, by increasing the villi height, the abundance of AA transporters, and the SC of most indispensable AA in pigs exposed to HS conditions. However, the lack of effect of supplemental Arg on both Lys SC and weight gain of pigs suggests that increasing the Lys content in the +Arg diet might be needed to improve the performance of HS pigs.

166 Optimal tryptophan:lysine Ratio for 25–40 Kg Growing Pigs Fed Diets Containing 35 % Distillers Dried Grains with Solubles

Distillers dried grains with solubles (DDGS) has a high concentration of Leu, and the Trp requirement for growing pigs may be increased if diets contain excess Leu. Therefore, the objective of this experiment was to determine the optimum standardized ileal digestible (SID) Trp:Lys ratio in growing pigs fed diets with excess Leu from DDGS. A diet based on corn, soybean-meal, and 35% DDGS was formulated to be deficient in Trp and Lys, according to NRC requirements (0.13% SID Trp; 0.88% SID Lys; 15% SID Trp:Lys ratio). Four diets were prepared by adding L-Trp to the basal diet, which resulted in analyzed SID Trp:Lys ratios of 18, 20, 23, and 24% in these diets. One-hundred and twenty growing pigs (26.3 ± 2.0 kg) were allotted to one of the 5 dietary treatments with 3 pigs per pen and 8 pen replicates in a completely randomized design. Diets were fed for 21d and blood samples were collected on d-21. Data were analyzed by linear and quadratic contrasts in SAS. The optimal SID Trp:Lys ratio was estimated using linear broken-line (LBL) and quadratic broken-line (QBL) regressions for ADG and G:F, using NLIN procedure in SAS. Results indicated that average daily feed intake, ADG, G:F, and final body weight increased (linear and quadratic, P &lt; 0.01) and plasma-urea-nitrogen decreased (linear and quadratic, P &lt; 0.05) as dietary SID Trp:Lys increased (Table 1). The SID Trp:Lys ratio to optimize ADG was 20.9 and 23.4% by LBL and QBL, respectively. The G:F was optimized at 18.7 and 20.2% by LBL and QBL, respectively. The average SID Trp:Lys ratio for the 4 measurements was 20.8% which is greater than the current NRC requirement (SID 17.3%). In conclusion, diets formulated with 35% DDGS may need more dietary Trp than current NRC values.

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217 Effects of Dietary Protein Content and Crystalline Amino Acid Supplementation Patterns on Growth Performance of Weaned Pigs Raised Under Different Sanitary Conditions

The objective of this experiment was to determine the effects of dietary crude protein (CP) content and crystalline amino acids (CAA) supplementation patterns on the growth performance of weaned pigs under clean (CSC) or unclean sanitary conditions (USC). One hundred forty-four piglets (6.35 ± 0.63 kg BW) were housed under CSC or USC for 3 wk and assigned to 1 of 3 diets: a high CP (HCP; 21%) and two low CP (LCP; 18%) diets supplemented with 10 crystalline indispensable amino acids (IAA) to meet all IAA requirements or only 6 IAA (Lys, Met, Thr, Trp, Val, and Ile) to meet IAA requirements except Leu, His, and Phe. Each treatment had 8 replicates (3 pigs per pen) per sanitary condition. The CSC room was cleaned and washed weekly. For the USC room, sow manure was spread and remained unwashed. Data were analyzed using the MIXED procedure of SAS with orthogonal polynomial contrasts. Pigs raised under USC had reduced (P &lt; 0.05) ADG and G:F in wk 2, but overall, no difference was found between sanitary conditions due to contrary results in wk 3. Overall, ADG and ADFI were not affected but G:F tended (P &lt; 0.10) to be lower for USC pigs. Also, G:F did not differ between HCP (0.79) and LCP (0.81) under CSC, however, LCP interactively decreased (P &lt; 0.05) G:F to 0.75 compared to 0.83 in HCP under USC. The CAA supplementation patterns did not influence growth except reduced (P &lt; 0.05) ADFI in wk 3. Pigs fed the HCP diet had higher (P &lt; 0.05) fecal scores throughout the experiment than those fed LCP diets under both sanitary conditions. In conclusion, overall growth performance did not differ between HCP and LCP under CSC, but LCP diets reduced G:F under USC. The fecal score decreased in LCP diets regardless of sanitary conditions.

210 A Longer Adaptation Period to a Functional Amino Acid-supplemented Diet Improves Growth Performance and Attenuates Acute-phase Response in Salmonella Typhimurium-challenged Pigs

Functional amino acid supplementation during disease challenge enhances growth performance and immune status. The present study investigated the effect of duration of adaptation period to a functional amino acid (FAA)-supplemented diet on growth performance and immune status during a subsequent Salmonella challenge in pigs. Thirty-two mixed-sex weanling pigs (8 pigs/treatment; 11.6 ± 0.34 kg initial body weight) received either a basal diet without FAA supplementation throughout the experimental period (FAA-) or a diet containing a supplemented FAA profile (Thr, Met, and Trp at 120% of requirements) fed for either 0 (FAA+0), 1 (FAA+1) or 2 (FAA+2) wk pre- and 1 wk post-inoculation with Salmonella Typhimurium (ST). Pigs were orally inoculated with saline containing ST after the 2 wk pre-inoculation period and monitored for 1 wk post-inoculation. Pigs had ad libitum access to diets throughout the experiment. Performance parameters [average daily gain (ADG), feed intake, and gain:feed (GF)] were measured in the pre- and post-inoculation periods. Blood samples were collected on d 0, 4, and 7 post-inoculation for serum haptoglobin and albumin analysis. There was no effect of diet on pre-inoculation performance (P &gt; 0.05). Post-inoculation, FAA+2 pigs had the highest ADG (0.46 kg/d) and GF (0.63 kg/kg), FAA- the lowest (0.21 kg/d; 0.29 kg/kg), with FAA+0 (0.33 kg/d; 0.46 kg/kg) and FAA+1 (0.40 kg/d; 0.53 kg/kg) being intermediate (ADG, P &lt; 0.05, SEM=0.059; GF, P &lt; 0.05, SEM=0.099). Overall, albumin was higher in FAA+2 (35.25 g/L) and FAA+1 (34.63 g/L) pigs compared to FAA+0 (30.38 g/L) and FAA- (29.67 g/L) pigs (P &lt; 0.05, SEM=0.717). Furthermore, FAA+2 pigs had the lowest overall haptoglobin (0.90 g/L), FAA- the highest (1.54 g/L), with FAA+0 (1.32 g/L) and FAA+1 (1.06 g/L) being intermediate (P &lt; 0.05, SEM=0.111). In conclusion, a longer adaptation period to FAA supplementation improved performance and attenuated the immune response of pigs when exposed to an enteric disease challenge.

A longer adaptation period to a functional amino acid-supplemented diet improves growth performance and immune status of Salmonella Typhimurium-challenged pigs

We recently showed that dietary supplementation with key functional amino acids (FAA) improves growth performance and immune status of Salmonella Typhimurium (ST)-challenged pigs. It is not known if ST-challenged pigs will benefit from a longer adaptation period to FAA. The objective of this study was to evaluate the effects of different adaptation periods to diets containing FAA above requirements for growth on performance and immune response of weaned pigs subsequently challenged with ST. A total of 32 mixed-sex weanling pigs (11.6 ± 0.3 kg) were randomly assigned to 1 of 4 dietary treatments, being a basal amino acid (AA) profile fed throughout the experimental period (FAA-) or a functional AA profile (FAA+; Thr, Met, and Trp at 120% of requirements) fed only in the postinoculation (FAA+0), for 1 wk pre- and postinoculation (FAA+1), or throughout the experimental period (FAA+2). After a 14-d adaptation period, pigs were inoculated with ST (2.15 × 109 CFU/mL). Growth performance, body temperature, fecal score, acute-phase proteins, oxidant/antioxidant balance, score for ST shedding in feces and intestinal colonization, and fecal and digesta myeloperoxidase (MPO) were measured pre- and postinoculation. Postinoculation body temperature and fecal score, serum haptoglobin, plasma superoxide dismutase (SOD), malondialdehyde (MDA), and fecal MPO were increased while serum albumin and plasma reduced glutathione (GSH):oxidized glutathione (GSSG) were reduced compared to pre-inoculation (P < 0.05). Average daily gain and G:F were greater in FAA+2 pigs compared to FAA- pigs (P < 0.05). Serum albumin was higher in FAA+2 and FAA+1 compared to FAA+0 and FAA- pigs (P < 0.05) while FAA+2 pigs had lower haptoglobin compared to FAA- (P < 0.05). Plasma SOD was increased and GSH:GSSG was decreased in FAA- pigs compared to the other treatments (P < 0.05). Score for ST shedding in feces was progressively lower from d 1 to 6 regardless of treatment (P < 0.05) and was lower in FAA+2 pigs compared to FAA- and FAA+0 (P < 0.05). Counts of ST in colon digesta were higher in FAA- and FAA+0 pigs compared to FAA+2 (P < 0.05). Fecal and colonic digesta MPO were lower in FAA+2 and FAA+1 pigs compared to FAA- (P < 0.05). These results demonstrate a positive effect of a longer adaptation period to FAA-supplemented diets on performance and immune status of weaned pigs challenged with Salmonella.

Bioavailability of the calcium salt of dl-methionine hydroxy analog compared with dl-methionine for nitrogen retention and the preference of nursery pigs for diets based on the 2 forms of methionine

Experiments were conducted to determine the relative bioavailability (RBV) of the calcium salt of the hydroxy analog of dl-methionine (MHA-Ca, 84%) to dl-methionine (dl-Met, 99%) as Met sources fed to pigs. In experiment 1, 42 crossbred barrows (initial BW of 15.0 ± 0.7 kg) were allotted to 7 treatments in an N-balance study. The basal diet (BD) was formulated to contain 15.4% CP and 0.22% Met (70% of requirement). Diets included (1) BD, (2) BD + 0.025% dl-Met, (3) BD + 0.050% dl-Met, (4) BD + 0.075% dl-Met, (5) BD + 0.038% MHA-Ca, (6) BD + 0.077% MHA-Ca, and (7) BD + 0.115% MHA-Ca. An increase in dietary inclusion rates of both Met sources linearly increased (P < 0.01) N retained (g/d) and N retention (% of intake). Using linear slope-ratio regression, the RBV value of MHA-Ca to dl-Met for N retained (g/d) was 63.0% on a product-to-product basis (75.0% on an equimolar basis). In experiment 2, 40 crossbred barrows (initial BW of 15.5 ± 1.5 kg) were allotted to 5 treatments in another N-balance study. The BD was formulated to contain 17.0% CP and 0.22% Met (70% of requirement). Diets included (1) BD, (2) BD + 0.030% dl-Met, (3) BD + 0.060% dl-Met, (4) BD + 0.046% MHA-Ca, and (5) BD + 0.092% MHA-Ca. Increasing levels of dl-Met or MHA-Ca increased N retained (g/d) and N retention (% of intake) linearly (P < 0.001) and quadratically (P < 0.05). Using linear slope-ratio regression, a product-to-product RBV value of MHA-Ca to dl-Met was 68.4% (81.4% on an equimolar basis) for N retained (g/d). In experiment 3, 276 pigs (12 barrow and 11 gilt replicates; initial BW of 7.09 ± 1.1 kg) were used in 3 diet preference studies. Pigs were randomly allotted to 1 of 3 treatment comparisons of feed choice: (1) BD (0.23% Met) or BD + 0.07% dl-Met; (2) BD or BD + 0.0825% MHA-Ca, and (3) BD + 0.07% dl-Met or BD + 0.0825% MHA-Ca. Pigs consumed a higher percentage (55 vs. 45%; P = 0.008) of their total feed intake from the diet supplemented with 0.07% dl-Met in Comparison 1, but a lower percentage (45 vs. 55%; P = 0.003) of their total feed intake from the diet supplemented with 0.0825% MHA-Ca in Comparison 2. There was no diet preference for dl-Met or MHA-Ca in Comparison 3. The observed Met source preference differences occurred in the barrow replicates but not in the gilt replicates. These results demonstrated the mean RBV of MHA-Ca to dl-Met of 65.7% on a product-to-product (wt/wt) basis or 78.2% on an equimolar basis and that a preference for Met sources was observed in barrows but not in gilts.

Efficiency of standardized ileal digestible lysine utilization for whole body protein deposition in pregnant gilts and sows during early-, mid-, and late-gestation

The efficiency of SID Lys utilization (kSID Lys) in gilts and sows during early (days 48 to 52), mid (days 75 to 79), and late gestation (days 103 to 107) was investigated using 88 pregnant females (PIC 1050; 27 gilts, 27 parity 1 sows, 34 parity 2+ sows; 192.96 ± 22.84 kg at days 42 ±1 of gestation) and whole body nitrogen (N) retention balance studies. Females were assigned to 1 of 4 SID Lys levels ranging from 40% to 70% of the daily SID Lys requirements above maintenance for a parity 1 sow according to the NRC (2012) gestating sow model in each gestation period. Experimental diets were isocaloric (3,335 kcal ME/kg) and isoproteic (11.75 % CP) and dietary indispensable AA were set to meet or exceed 100% of AA:Lys ratios. The slope of the linear response to graded SID Lys intake was defined as kSID Lys. With the aim of increasing the accuracy of kSID Lys estimates, gilt data from the current study was combined with gilt data from a previous study conducted at the same facility using 4 SID Lys levels ranging from 60% to 90% of the daily SID Lys requirements above maintenance for gilts according to the NRC (2012) gestating sow model. Whole body Lys retention of the combined gilt data set was assessed with different broken-line and nonlinear models. The kSID Lys was 0.65, 0.38, and 0.52 for early-, mid-, and late-gestation, respectively, in gilts. A linear response to graded SID Lys intake was found in late gestation only in parity 1 and 2+ sows; kSID Lys was determined as 0.44 and 0.52 in late gestation for parity 1 and parity 2+ sows, respectively. There were no differences in kSID Lys in late gestation between parities. For the combined gilt data, the model of best performance (reduced error and greater goodness of fit) was the Hoerl model. Maximum kSID Lys (i.e., g SID Lys retention/g SID Lys intake) in gilts was 0.67, 0.54, and 0.53 in early, mid, and late gestation predicted at 7.2, 9.1, and 13.5 g of SID Lys intake/d, respectively, based on the Hoerl model. Maximum SID Lys retention in gilts was similarly predicted at 8.5, 10.5, and 20.9 g of SID Lys intake per day in early, mid, and late gestation and resultant kSID Lys of 0.61, 0.51, and 0.44, respectively. The findings of this study demonstrate that kSID Lys varies by stage of gestation and SID Lys intake level and that, at least in gilts, a dynamic kSID adjusted for daily intake more adequately reflects biological response and hence allows more precise feeding of pregnant females.

Functional amino acid supplementation, regardless of dietary protein content, improves growth performance and immune status of weaned pigs challenged with Salmonella Typhimurium

High dietary protein may increase susceptibility of weaned pigs to enteric pathogens. Dietary supplementation with functional amino acids (FAA) may improve growth performance of pigs during disease challenge. The objective of this study was to evaluate the interactive effects of dietary protein content and FAA supplementation above requirements for growth on performance and immune response of weaned pigs challenged with Salmonella. Sixty-four mixed-sex weanling pigs (13.9 ± 0.82 kg) were randomly assigned to dietary treatments in a 2 × 2 factorial arrangement with low (LP) or high protein (HP) content and basal (AA-) or FAA profile (AA+; Thr, Met, and Trp at 120% of requirements) as factors. After a 7-d adaptation period, pigs were inoculated with either a sterile saline solution (CT) or saline solution containing Salmonella Typhimurium (ST; 3.3 × 109 CFU/mL). Growth performance, body temperature, fecal score, acute-phase proteins, oxidant/antioxidant balance, ST shedding score in feces and intestinal colonization, fecal and digesta myeloperoxidase (MPO), and plasma urea nitrogen (PUN) were measured pre- and postinoculation. There were no dietary effects on any measures pre-inoculation or post-CT inoculation (P > 0.05). Inoculation with ST increased body temperature and fecal score (P < 0.05), serum haptoglobin, plasma superoxide dismutase (SOD), malondialdehyde (MDA), PUN, and fecal MPO, and decreased serum albumin and plasma reduced glutathione (GSH):oxidized glutathione (GSSG) compared with CT pigs (P < 0.05). ST-inoculation reduced average daily gain (ADG) and feed intake (ADFI) vs. CT pigs (P < 0.05) but was increased by AA+ vs. AA- in ST pigs (P < 0.05). Serum albumin and GSH:GSSG were increased while haptoglobin and SOD were decreased in ST-inoculated pigs fed AA+ vs. AA- (P < 0.05). PUN was higher in HP vs. LP-fed pigs postinoculation (P < 0.05). Fecal ST score was increased in ST-inoculated pigs on days 1 and 2 postinoculation and declined by day 6 (P < 0.05) in all pigs while the overall score was reduced in AA+ vs. AA- pigs (P < 0.05). Cecal digesta ST score was higher in HP vs. LP-fed pigs and were lower in AA+ compared with AA- fed pigs in the colon (P < 0.05). Fecal and digesta MPO were reduced in ST pigs fed AA+ vs. AA- (P < 0.05). These results demonstrate a positive effect of FAA supplementation, with minimal effects of dietary protein, on performance and immune status in weaned pigs challenged with Salmonella.

Evaluating the standardized ileal digestible lysine requirement of 7- to 15-kg weanling pigs fed corn-soybean meal-based diets

Continued genetic improvement necessitates the verification of nutrient requirements for newly developed pig genotypes. Therefore, the objective of this research was to determine the standardized ileal digestible (SID) lysine (Lys) requirement of 7- to 15-kg weanling pigs (TN70 × TN Tempo; Topigs Norsvin) fed a corn-soybean meal-based diet. A total of 144 piglets with an initial BW of 6.51 ± 0.56 kg (mean ± SD) were assigned to one of six diets using a randomized complete block design based on BW to give eight replicate pens with three pigs per pen. The six diets contained 1.00, 1.16, 1.32, 1.48, 1.64, and 1.80% SID Lys, achieved by adding crystalline l-Lys·HCl at the expense of cornstarch. Other indispensable amino acids were provided to meet the requirements. Piglets had free access to diets and water for 21 days. Individual BW of pigs and feed disappearance were recorded weekly and blood samples were collected on day 1, 14, and 21. Average daily gain (ADG) and average daily feed intake were not affected by dietary SID Lys content during the first 7 days. However, the addition of dietary SID Lys quadratically increased (P < 0.05) gain:feed (G:F) during the first 7 days of the experiment. A quadratic increase (P < 0.05) was found in both ADG and G:F when SID Lys content increased in the diets from day 14 to 21. During the overall experimental period, increasing dietary Lys content quadratically increased (P < 0.05) ADG and G:F, whereas plasma urea nitrogen quadratically decreased (P < 0.05) as SID Lys content increased. The SID Lys requirements were estimated for linear and quadratic broken-line models. In conclusion, the SID Lys requirement for optimal growth performance of 7- to 15-kg weanling pigs fed corn-soybean meal-based diets based on linear and quadratic broken-line models were 1.27% (95% confidence interval (CI): [1.01, 1.53]) and 1.30% (95% CI: [0.94, 1.66]) for ADG and 1.27% (95% CI: [1.14, 1.40]) and 1.43% (95% CI: [1.11, 1.75]) for G:F, respectively, thus giving an overall average value of 1.32%.

203 Efficiency of SID lysine utilization and maximum SID lysine retention for gilts in early, mid and late gestation

Efficiency of amino acid (AA) use is presumed constant across gestation but may not reflect changes in metabolic demand during gestation nor consider changes in efficiency depending on level of AA intake. Two experiments were conducted to determine efficiency of SID Lys utilization in gilts during early (d 48-52), mid (d 75-79) and late gestation (d 103-107). Each experiment provided 4 isocaloric (3,335 kcal ME/kg) and isoproteic (11.75 % CP) diets containing 4 SID Lys levels (Table 1). Diets were randomly assigned to 45 gilts (PIC 1050, 158.0 ± 8.0 kg at d 39.4 ± 1 of gestation) in Exp. 1 and 27 gilts (PIC 1050, 169.0 ± 7.5 kg at d 41 ± 1 of gestation) in Exp. 2. Dietary indispensable AA were set to meet or exceed 100% of AA:Lys ratios in both experiments. The SID Lys retention was estimated from whole body nitrogen (N) retention balance studies in each period (7 d diet adaptation, 5 d total urine collection and grab fecal sampling) according to the NRC (2012) equations. The relationship between SID Lys intake and SID Lys retention was determined by nonlinear regression models using the CurveExpert Professional software. According to the Hoerl regression model: E(y)=exp(β 0+β 1X)[Xβ2] best-fitting line, maximum efficiency of SID Lys utilization (i.e. g SID Lys retention/g SID Lys intake) was 65%, 57%, and 53% in early, mid and late gestation and occurred at 6.6, 8 and 12 g of SID Lys intake/d, respectively. Maximum SID Lys retention occurred at 8.1 and 9.8 g of SID Lys intake/d for early and mid-gestation. The SID Lys retention did not reach a maximum value in late gestation. These results suggest that efficiency of SID Lys utilization is not constant across gestation and that maximal efficiency occurs at intake below current recommendations.

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210 Effects of D-methionine compared with L-methionine on N retention, gut morphology and antioxidant status of weaned pigs

A N-balance study was conducted to compare the effect of D-methionine (D-Met) or L-methionine (L-Met) supplementation on N balance, gut morphology and antioxidant status of weaned pigs. Fifty-six weaned barrows (10.5 ± 1.2 kg initial BW) were allotted to 7 diets in 2 blocks. A Met-deficient basal diet (BD; 0.24% standardized ileal digestible (SID) Met) but adequate in other AA, was supplemented with 3 graded levels (0.036, 0.072, and 0.108%) of D-Met or L-Met. After a 7-d adaptation, feces and urine were collected quantitatively for 5 d to determine N balance. At the completion of the experiment, blood samples were collected from all pigs. Pigs fed the BD and pigs fed the highest level of SID Met (0.34%) of both Met sources were euthanized and tissue samples from liver, kidney, muscle (longissimus dorsi), duodenal and jejunal mucosa were collected. N retention as % of N intake increased (P &lt; 0.001; 67, 72, 73, 74, 71, 74, 74%, respectively) by graded supplemental level of D-Met or L-Met. However, there was no interaction between Met source and supplemental level for all N-balance metrics. Using a slope-ratio regression, the bioavailability of D-Met relative to L-Met was 100.1% (95% confidence intervals: 85-116%) based on N retention (% of N intake). Villus height and crypt depth in the duodenum and jejunum were not affected by Met sources. Pigs fed the D-Met diet had a greater (P &lt; 0.05) total glutathione concentration in liver (4.9 vs. 1.5 µM) vs. BD. However, total antioxidant capacity and concentration of thiobarbituric acid-reactive substances in liver, muscle or plasma samples were not different among treatments. Supplementation with D-Met increased glutathione peroxidase activity in kidney (878 vs. 413 and 229 mU/mL; P &lt; 0.05) compared with BD or L-Met diet, however, activity of glutathione reductase in liver and kidney were not affected by treatments. These data indicate that D-Met and L-Met are equally efficient to support N retention, intestinal morphology and oxidative status in weaned pigs.

PSIII-34 Standardized ileal digestible lysine requirements for 7- to 15-kg weanling pigs with high-lean genetics fed a corn-soybean meal-based diet

Continued genetic improvement necessitates the verification of nutrient requirements for newly developed pig genotypes. Therefore, the objective was to determine the standardized ileal digestible (SID) lysine requirements for 7- to 15-kg high-lean piglets (TN Tempo × TN70) fed a corn-soybean meal-based diet. A total of 144 piglets (6.51 ± 0.56 kg BW) were assigned to 1 of 6 diets in a randomized complete block design based on BW to give 8 replicate pens each with 3 pigs over a 21-d period. Sex was balanced as 4 replicates for each male and female. Diets contained 1.00, 1.16, 1.32, 1.48, 1.64, or 1.80% SID lysine, achieved by adding crystalline L-Lysine·HCl at the expense of cornstarch. Other indispensable AA were provided to meet the requirements. Individual BW and feed disappearance were recorded weekly and blood was sampled on d 1, 14, and 21. Data were analyzed using MIXED procedure of SAS including the SID lysine concentration as the fixed effect and the block as the random effect. Sex effect was not significant, thus was excluded from the model. The SID Lys requirements were estimated for linear and quadratic broken-line using NLIN procedure of SAS. Lysine content did not affect ADG and ADFI during wk 1, but quadratically increased (P &lt; 0.05) G:F. From d 14 to 21, ADG and G:F increased (P &lt; 0.05) quadratically by increasing dietary lysine content. Overall, increasing dietary lysine content quadratically increased (P &lt; 0.05) ADG and G:F; whereas, plasma urea nitrogen quadratically decreased (P &lt; 0.05). In conclusion, the SID lysine requirements for optimal growth performance of 7- to 15-kg piglets fed corn-soybean meal-based diets based on linear and quadratic broken-line models were 1.27 and 1.38% for ADG and 1.36 and 1.46% for G:F, respectively, thus giving an overall average value of 1.37%.

14 Challenges and opportunities for formulating low-protein diets for maintaining growth and N-retention of weanling and growing-finishing pigs

For more than two decades, numerous studies have been conducted evaluating the effects of lowering CP level in pig diets. It is now accepted that lowering dietary CP level and adding crystalline amino acids (CAA) improves N utilization and consequently reduces N excretion. Increased availability of CAA such as Lys, Thr, Met, Trp, Val (Ile, Arg and His) allows nutritionists to further reduce dietary CP level while meeting pigs’ AA requirements more closely. However, pig performance was sometimes compromised when the dietary CP level was reduced more than 4 percentage units and adding high inclusion levels of CAA. An increase in backfat thickness was also sometimes reported when feeding finishing pigs with low CP diets. The potential reasons for such inconsistent results are due to the deficiency of the next limiting AA (typically Val and Ile), inaccurate feed mixing and insufficient amount of non-essential AA (NEAA) in the low CP diets. Formulating low CP diets on similar energy content as for the high CP diets on ME basis sometimes led to a greater backfat thickness in finishing pigs which was mainly due to increased energy utilization of pigs fed low CP diets coupled with the excess energy being stored as carcass fat. Based on the results of these experiments, optimal growth performance, carcass quality and N retention of pigs can be maintained when low CP diets are balanced for adequate levels of both essential AA and NEAA on the standardized ileal digestible basis combined with formulating on NE basis. Research suggests that keeping a maximum total Lys:CP ratio of 7.4% could overcome deficiency of NEAA in the low CP diets. Based on published N-balance studies, 1 percent unit dietary CP reduction results on average 9% reduction in N excretion in pigs which is an effective approach to become more sustainable pork production.

200 Reduced growth performance of pigs fed methionine deficient diet may be associated with their reduced muscle cell differentiation

Methionine (Met) is the second or third limiting AA in typical swine diets and plays important roles in promoting the growth, especially, the muscle growth of pigs. This research studied the effects of dietary Met restriction on growth performance and myogenic gene expression in growing pigs. Eight genes in two families, including myogenic regulatory factor family comprising myogenic differentiation 1 (MyoD1), myogenic factor 5 (Myf5), myogenin (MyoG) and myogenic factor 6 (Myf6), and myocyte enhancer factor 2 (Mef2) family comprising Mef2A, Mef2B, Mef2C and Mef2D, were selected for analysis. Individually penned barrows (crossbred, 23.6±2.4 kg) were randomly assigned to two dietary treatments. A basal diet (Diet 1; Met-deficient) was formulated to contain 0.22% standardized ileal digestible (SID) Met and 0.52% SID Met+Cys but to meet the NRC (2012) recommendations for other nutrients. Crystalline DL-Met was added to the basal diet to generate Diet 2 adequate in Met (0.37% SID Met, 0.67% SID Met+Cys). During the four-week ad libitum feeding trial, ADG, ADFI and G:F were measured. Immediately before and after the trial, muscle samples were collected from the longissimus dorsi using a standard biopsy protocol. Total RNA was extracted from the muscle samples (TRIzol Reagent; Invitrogen) and subjected to cDNA reverse-transcription (QuantiTect Reverse Transcription Kit; Qiagen). Transcribed cDNA were used for qPCR analysis (Rotor-Gene Q System; Qiagen). Comparative ΔΔCT method was used for quantitation. Data were analyzed with Student’s T-test. Pigs fed Diet 1 (vs. Diet 2) had a lower ADG and G:F (P&lt; 0.01). Before the feeding trial, all the tested genes had comparable mRNA levels between the two treatments (P &gt;0.17). After the trial, Diet 1 pigs showed tendency for lower levels of Myf6 and Mef2D mRNA (P&lt; 0.09). These results suggest that the reduced ADG and G:F is associated with the possibly-reduced muscle cell differentiation in pigs fed Met-deficient diet.

199 Supplemental arginine affects intestinal gene expression and serum concentration of amino acids of heat stress pigs

The exposure of pigs to heat stress (HS) reduces feed intake and can damage their intestinal epithelia, affecting the amino acid (AA) absorption. Because Arg is involved in the restoration of intestinal epithelia cells and HS reduces Arg intake, the effect of dietary supplementation with Arg above requirement on the expression of specific AA transporters and the serum concentration (SC) of free AA in HS pigs was analyzed. Twenty pigs (25.3 ± 4.4 kg BW) were randomly assigned to one of two dietary treatments: control wheat-soybean meal diet supplemented with L-Lys and L-Thr (CON), and the CON diet added with 0.20% L-Arg (ARG). Pigs had at libitum access to feed and water. At the end of a 21-d trial, 6 pigs per treatment were sacrificed; blood and intestinal mucosa samples from each segment of the small intestine were collected to analyze the SC of AA and the expression of AA transporters, respectively. Ambient temperature (AT) ranged from 28.2 to 38.7 °C. Supplementation of L-Arg increased approx. 5x the abundance of mRNA coding for the synthesis of AA transporter b0,+ (P&lt; 0.05) and tended to increase that of the AA transporter B0 (P&lt; 0.10) in duodenum, but no effect on gene expression in jejunum and ileum was observed. The SC of AA (mg/dL) for CON and ARG pigs were: Arg, 27.40, 38.32; His, 9.64, 12.9; Ile, 14.33, 15.73; Leu, 23.32, 29.97; Lys, 31.67, 39.72; Met, 5.14, 8.22; Phe, 15.18, 18.07; Thr, 20.82, 31.55; Trp, 8.50, 11.32; Val, 22.47, 33.35, respectively. Supplementation of L-Arg increased serum Arg, His, Met, Thr, Trp, and urea (P&lt; 0.05); tended to increase Val (P&lt; 0.10), but did not affect Ile, Leu, Lys, and Phe (P &gt;0.10). These results indicate that supplementation of L-Arg may help to recover the intestinal epithelia, improve the absorptive function of the small intestine, and increase the availability of some indispensable AA in HS pigs.

369 Amino acid nutrition in monogastrics: going beyond the ideal protein

In addition to serving as building blocks for protein synthesis, AA are also involved in various important metabolic pathways in the body. Amino acids that regulates key metabolic pathways to improve health, growth, development and reproduction are considered as functional AA. The roles of AA for immune function have received more attention in recent years. Methionine serves as a methyl donor for important processes such as DNA methylation, polyamine synthesis and is a precursor to form Cys, which is needed for the synthesis of a major antioxidant glutathione. Tryptophan is involved in various metabolic pathways, including immune response and the formation of serotonin which involves in feed intake regulation. Threonine plays a key role in immune function through its incorporation into immunoglobulins and is preferentially utilized by the gut in pigs partly for synthesis of mucosal proteins including mucins which are high in Thr. The branched-chain amino acids (Leu, Val, Ile) are involved in maintaining intestinal barrier function, enterocyte proliferation and immune defenses in pigs. The other functional AA include Gln, Arg and Gly which are involved in immune system functioning and gut health. During sub-clinical level of diseases or inflammation, nutrients are prioritized to form tissues involved in immune response compromising growth, implying that the requirement of some key AA is increased to maintain immune function. Adjusting the ideal ratio of these functional AA to Lys in diets may maintain gut health and promote growth, because it can enhance immune status and gut integrity for weaned pigs, especially when sanitary and climatic conditions are challenging, and antibiotics are not or less used in the diets. Future research is warranted to quantitatively estimate the increased need of these functional AA in pigs raised under sub-optimal conditions as well as evaluate the interaction or synergistic effect of these AA on animals’ immunity.

118 Functional amino acid supplementation, regardless of dietary protein content, improves growth performance, acute-phase response, and bacterial shedding in Salmonella-challenged pigs

The present study investigated the interactive effect of functional amino acid (AA) supplementation and dietary protein level on growth performance and immune status in Salmonella-challenged pigs. Thirty-two growing pigs (8 pigs/treatment; 13.9 ± 0.82 kg initial body weight) had ad libitum access to 1 of 4 experiment diets in a 2×2 factorial arrangement with factors of dietary protein (LP: Low, 16% protein vs. High: HP, 20% protein) and 2 levels of functional AA supply (AA-: basal vs. AA+: Thr, Met, and Trp provided at 20% above requirement). After 7 d of adaptation, pigs were orally inoculated with saline containing Salmonella typhimurium (ST). Performance parameters [average daily gain (ADG), feed intake, and gain:feed (GF)] were measured in the pre- and post-inoculation periods. Blood samples were collected on d0, 4 and 7 post-inoculation for serum haptoglobin and albumin analysis. Shedding of ST (d1, 2, 4 and 6 post-inoculation) and quantification in digesta (ileum, cecum and colon; d7 post-inoculation) were analyzed. There was no effect of diet on pre-inoculation performance (P &gt; 0.05). Pigs fed AA+ showed increased ADG (0.457 vs. 0.298 ± 0.051 kg/d; P &lt; 0.05) and a trend for improved GF (0.67 vs. 0.40 ± 0.07 kg/kg; P &lt; 0.10) post-inoculation compared to AA- regardless of dietary protein level. Feeding AA+ increased overall albumin levels (35.7 vs. 34.2 ± 0.9 g/L; P &lt; 0.05) and decreased overall haptoglobin levels (1.64 vs. 1.81 ± 0.12 g/L; P &lt; 0.05) and decreased overall shedding score of ST (2.27 vs. 2.51 ± 0.09; P &lt; 0.05) compared to AA-. The ST counts in cecal digesta increased (2.78 vs. 2.23 ± 0.18 Log10 cfu/g; P &lt; 0.05) in pigs fed HP compared to LP-fed pigs and ST counts in colon were reduced (2.08 ± 0.18 vs. 2.61 ± 0.19 Log10 cfu/g; P &lt; 0.05) in AA+ compared to AA- pigs. Supplementation of diets with specific functional AA improved performance and health status of pigs when exposed to an enteric disease challenge.

Crystalline amino acids do not influence calculated values for standardized ileal digestibility of amino acids in feed ingredients included in diets for pigs

An experiment was conducted to test the hypothesis that addition of crystalline amino acids (AA) to diets during the adaptation or collection periods will not influence calculated values for apparent ileal digestibility (AID) or standardized ileal digestibility (SID) of AA in corn and soybean meal (SBM). Seven ileal-cannulated barrows (initial body weight: 77.9 ± 2.6 kg) were allotted to a 7 × 7 Latin Square design with 7 dietary treatments and 7 periods. Dietary treatments included feeding diets based on corn or SBM without or with crystalline AA for the entire 7-d period or with crystalline AA during the adaptation period, but without crystalline AA during the collection period. An N-free diet was also used. Each experimental period consisted of 5 d of adaptation to the diets followed by 2 d of ileal digesta collection, with digesta being collected for 9 hr/d starting after feeding the morning meal. Thus, the entire experiment lasted 49 d. The AID and SID of crude protein (CP) and AA were calculated using values determined in corn or in SBM without or with crystalline AA to determine if crystalline AA influenced calculated values for AID or SID of CP and AA. Results indicated that addition of crystalline AA to diets fed during the entire 7-d period increased (P < 0.05) AID of some AA in corn and SBM. However, no differences in SID of CP and AA were observed between pigs fed the diets without crystalline AA and pigs fed the diets with crystalline AA if dietary crystalline AA were ignored in calculations of SID values. This indicates that crystalline AA were 100% absorbed before the distal ileum and did not affect calculated values for SID of AA if calculations were based only on the AA in corn or SBM. Therefore, it is concluded that crystalline AA may be added to experimental diets in digestibility experiments before and during collection periods without affecting results, if crystalline AA are disregarded in the calculation of AID or SID of AA in ingredients.

The effect of reduced dietary glycine and serine and supplemental threonine on growth performance, protein deposition in carcass and viscera, and skin collagen abundance of nursery pigs fed low crude protein diets

Thirty five barrows (initial body weight [BW]: 15.1 ± 1.0 kg) were used to determine the effect of partially replacing Gly + Ser with Thr in reduced crude protein (CP) diets on growth performance, protein deposition in carcass and viscera, and skin collagen abundance during the late nursery phase to 25 kg BW. Pigs were individually fed one of five iso-nitrogenous diets (n = 7) for 21 d. The basal diet met estimated essential amino acids (AA) requirements by using all essential AA plus Gly and Ser in free form (CON; 12.1% CP; as-fed, analyzed contents). The remaining four diets were formulated by reducing total Gly and Ser concentrations to 60% or 20% of the CON diet. The N removed with Gly and Ser was replaced with either crystalline Thr or Glu. Total analyzed Thr made up either 1.59% (T1; 12.5% CP) or 2.34% (T2; 12.2% CP) of the Thr-supplemented diets, and total analyzed Glu made up either 3.47% (G1; 12.7% CP) or 4.64% (G2; 12.9% CP) of the Glu-supplemented diets. Pigs were slaughtered on day 21 to determine body composition and skin collagen abundance via bright field microscopy. Overall, average daily gain (ADG) and G:F and final carcass weights were greater for pigs fed diets supplemented with Glu (G1 + G2) vs. those fed diets supplemented with Thr (T1 + T2; P < 0.05, P = 0.060, and P = 0.050 for ADG, G:F, and final carcass weight, respectively); intermediate values were observed for CON. Nitrogen retention in carcass plus viscera and the AA profile of deposited protein in the carcass were not influenced by dietary treatment. Pigs fed the T2 and G2 diets had greater retention of Thr (vs. CON and G2) and Glu (vs. CON and T2) in the viscera protein, respectively (P < 0.05). The apparent utilization efficiency of standardized ileal digestible Thr for protein deposition in carcass plus viscera was less for pigs fed T2 (15.1%) vs. those fed CON (56.7%) or G2 (58.6% ± 2.9%) diets (P < 0.001). Only pigs fed T1 had skin collagen abundance not different from CON; pigs fed G1, G2, and T2 had reduced skin collagen abundance compared with CON and T1 (P < 0.01). Using Glu as an N source when Gly and Ser were reduced to 60% and 20% of CON in reduced CP diets maintained ADG for pigs between 15 and 25 kg BW, whereas supplying Thr as a N source reduced ADG and carcass weight. When dietary Gly and Ser were supplied at 60% of CON, only Thr supplementation rescued skin collagen abundance. Therefore, supplemental Thr at excess levels is not sufficient to replace N from Gly and Ser in reduced CP diets fed to late nursery pigs, despite supporting skin collagen abundance as a secondary indicator of Gly status.

Growth performance and gut health of Escherichia coli-challenged weaned pigs fed diets supplemented with a Bacillus subtilis direct-fed microbial

This study was conducted to investigate the effects of a direct-fed microbial (DFM) product (Bacillus subtilis strain DSM 32540) in weaned pigs challenged with K88 strain of Escherichia coli on growth performance and indicators of gut health. A total of 21 weaned pigs [initial body weight (BW) = 8.19 kg] were housed individually in pens and fed three diets (seven replicates per diet) for 21 d in a completely randomized design. The three diets were a corn-soybean meal-based basal diet without feed additives, a basal diet with 0.25% antibiotics (neo-Oxy 10-10; neomycin + oxytetracycline), or a basal diet with 0.05% DFM. All pigs were orally challenged with a subclinical dose (6.7 × 10⁸ CFU/mL) of K88 strain of E. coli on day 3 of the study (3 d after weaning). Feed intake and BW data were collected on days 0, 3, 7, 14, and 21. Fecal scores were recorded daily. On day 21, pigs were sacrificed to determine various indicators of gut health. Supplementation of the basal diet with antibiotics or DFM did not affect the overall (days 0-21) growth performance of pigs. However, antibiotics or DFM supplementation increased (P = 0.010) gain:feed (G:F) of pigs during the post-E. coli challenge period (days 3-21) by 23% and 24%, respectively. The G:F for the DFM-supplemented diet did not differ from that for the antibiotics-supplemented diet. The frequency of diarrhea for pigs fed a diet with antibiotics or DFM tended to be lower (P = 0.071) than that of pigs fed the basal diet. The jejunal villous height (VH) and the VH to crypt depth ratio (VH:CD) were increased (P < 0.001) by 33% and 35%, respectively, due to the inclusion of antibiotics in the basal diet and by 43% and 41%, respectively due to the inclusion of DFM in the basal diet. The VH and VH:CD for the DFM-supplemented diet were greater (P < 0.05) than those for the antibiotics-supplemented diet. Ileal VH was increased (P < 0.05) by 46% due to the inclusion of DFM in the basal diet. The empty weight of small intestine, cecum, or colon relative to live BW was unaffected by dietary antibiotics or DFM supplementation. In conclusion, the addition of DFM to the basal diet improved the feed efficiency of E. coli-challenged weaned pigs to a value similar to that of the antibiotics-supplemented diet and increased jejunal VH and VH:CD ratio to values greater than those for the antibiotics-supplemented diet. Thus, under E. coli challenge, the test DFM product may replace the use of antibiotics as a growth promoter in diets for weaned pigs to improve feed efficiency and gut integrity.

Dietary protein-bound or free amino acids differently affect intestinal morphology, gene expression of amino acid transporters, and serum amino acids of pigs exposed to heat stress

Pigs exposed to heat stress (HS) increase body temperature in which can damage the intestinal epithelia and affect the absorption and availability of amino acids (AA). Protein digestion and metabolism further increase body temperature. An experiment was conducted with six pairs of pigs (of 47.3 ± 1.3 kg initial body weight) exposed to natural HS to assess the effect of substituting dietary protein-bound AA by free AA on morphology and gene expression of intestinal epithelial and serum concentration (SC) of free AA. Treatments were: high protein, 21.9% crude protein (CP) diet (HShp) and low protein, 13.5% CP diet supplemented with crystalline Lys, Thr, Met, Trp, His, Ile, Leu, Phe, and Val (HSaa). The HShp diet met or exceeded all AA requirements. The HSaa diet was formulated on the basis of ideal protein. Pigs were fed the same amount at 0700 and 1900 hours during the 21-d study. Blood samples were collected at 1700 hours (2.0 h before the evening meal), 2030 hours, and 2130 hours (1.5 and 2.5 h after the evening meal). At the end, all pigs were sacrificed to collect intestinal mucosa and a 5-cm section from each segment of the small intestine from each pig. Villi measures, expression of AA transporters (y+L and B0) in mucosa, and SC of AA were analyzed. Ambient temperature fluctuated daily from 24.5 to 42.6 °C. Weight gain and G.F were not affected by dietary treatment. Villi height tended to be larger (P ≤ 0.10) and the villi height:crypt depth ratio was higher in duodenum and jejunum of pigs fed the HSaa diet (P < 0.05). Gene expression of transporter y+L in jejunum tended to be lower (P < 0.10) and transporter B0 in the ileum was lower (P < 0.05) in HSaa pigs. Preprandial (1700 hours) SC of Arg, His, Ile, Leu, Thr, Trp, and Val was higher (P < 0.05), and Phe tended to be higher (P < 0.10) in HShp pigs. At 2030 hours (1.5 h postprandial), serum Lys, Met, and Thr were higher in the HSaa pigs (P < 0.05). At 2130 hours (2.5 h), Arg, His, Ile, Phe, and Trp were lower (P < 0.05); Met was higher (P < 0.05); and Lys tended to be higher (P < 0.10) in HSaa pigs. In conclusion, feeding HS pigs with low protein diets supplemented with free AA reduces the damage of the intestinal epithelia and seems to improve its absorption capacity, in comparison with HS pigs fed diets containing solely protein-bound AA. This information is useful to formulate diets that correct the reduced AA consumption associated with the decreased voluntary feed intake of pigs under HS.

The direct and difference procedures result in similar estimates for amino acid digestibility in feed ingredients fed to growing pigs

An experiment was conducted to test the hypothesis that values for standardized ileal digestibility (SID) of amino acids (AA) in corn, wheat, and wheat middlings obtained using the direct procedure are not different from values obtained using the difference procedure. Sixteen ileal-cannulated barrows (initial BW: 69.5 ± 5.0 kg) were allotted to a replicated 8 × 4 Youden Square design with 8 diets and 4 periods. Each period consisted of 5 d of adaptation to the diet and 2 d of collection of ileal digesta. Four diets were based on soybean meal (SBM), corn, wheat, or wheat middlings as the only AA-containing ingredients. Three additional diets were based on a mixture of SBM and corn, SBM and wheat, or SBM and wheat middlings, and an N-free diet was also used. The apparent ileal digestibility (AID) and the SID of crude protein (CP) and AA for the 4 diets containing SBM, corn, wheat, or wheat middlings as the sole source of AA were calculated using the direct procedure. The AID and SID of CP and AA for the 3 mixed diets containing SBM and corn, wheat, or wheat middlings were also calculated and the contribution of digestible AA from SBM was subtracted from the AID or SID values for the diets. The AID or SID of AA in corn, wheat, and wheat middlings were subsequently calculated by difference. Results indicated that the AID values for a few AA were lower (P < 0.05) if the direct procedure was used instead of the difference procedure, regardless of ingredient. The AID of Trp was greater in corn and wheat middlings, and the SID of Trp in corn and wheat middlings tended to be greater, if the direct procedure rather than the difference procedure was used, but that was not the case for wheat (interaction, P < 0.05 and P < 0.10, respectively). However, for all other indispensable AA, and for most of the dispensable AA, the SID of AA in corn, wheat, and wheat middlings was not different between the difference procedure and the direct procedure. Therefore, values for SID of AA in cereal grains and fiber-rich ingredients may be determined using either the direct or the difference procedure.

Dietary Supplementation of dl-Methionine Potently Induces Sodium-Dependent l-Methionine Absorption in Porcine Jejunum Ex Vivo

BACKGROUND

Methionine is an essential amino acid (AA) with many fundamental roles. Humans often supplement l-Met, whereas dl-Met and dl-2-hydroxy-4-(methylthio)butanoic acid (dl-HMTBA) are more frequently used to supplement livestock.

OBJECTIVES

The study aimed to investigate whether dietary Met source alters the absorptive capacity for Met isomers in the small intestine of piglets.

METHODS

A total of 27 male 10-wk-old piglets in 3 feeding groups received a diet supplemented with 0.21% dl-Met, 0.21% l-Met, or 0.31% dl-HMTBA to meet the Met + cystine requirement. After ≥10 d, absorptive fluxes of d-Met or l-Met were measured at a physiological concentration of 50 μM and a high concentration of 5 mM in duodenum, middle jejunum, and ileum ex vivo. Data were compared by 2-factor ANOVA.

RESULTS

Across diets, fluxes of both Met isomers at both tested concentrations increased from duodenum to ileum by a factor of ∼2-5.5 (P < 0.05). Pigs supplemented with dl-Met had greater (P < 0.085) absorptive fluxes at 50 μM l-Met (0.50, 2.07, and 3.86 nmol · cm-2 · h-1) and d-Met (0.62, 1.41, and 1.19 nmol · cm-2 · h-1) than did pigs supplemented with dl-HMTBA (l-Met: 0.28, 0.76, and 1.08 nmol · cm-2 · h-1; d-Met: 0.34, 0.58, and 0.64 nmol · cm-2 · h-1) in duodenum, jejunum, and ileum, respectively. Only in jejunum of dl-Met-fed pigs, fluxes at 50 μM l-Met were reduced by the omission of luminal Na+ (from 3.27 to 0.86 nmol · cm-2 · h-1; P < 0.05) and by a cocktail of 22 luminal AAs (to 1.05 nmol · cm-2 · h-1; P < 0.05).

CONCLUSIONS

Dietary supplementation of dl-Met increases the efficiency of l-Met and d-Met absorption at physiologically relevant luminal Met concentrations along the small intestine of pigs, including a very prominent induction of an Na+-dependent transport system with preference for l-Met in the mid-jejunum. Dietary supplementation with dl-Met could be a promising tool to improve the absorption of Met and other AAs.

Immune system stimulation increases the irreversible loss of cysteine to taurine, but not sulfate, in starter pigs

An isotope tracer study was conducted to evaluate the effects of immune system stimulation (ISS) on the irreversible loss of cysteine (Cys) to taurine (Tau) and sulfate (SO4), as well as glutathione (GSH) synthesis, during the fed state in pigs. We previously have reported that ISS increases plasma Cys flux and the GSH synthesis rate at the tissue and whole-body levels in growing pigs. Thus, the current article presents the data on the irreversible loss of Cys during ISS in pigs. Ten gilts (BW: 7.0 ± 0.12 kg) were feed restricted a sulfur amino acids (SAA) limiting diet and injected twice with either saline (n = 4) or increasing amounts of E. coli lipopolysaccharide (n = 6). The day after the second injection, a 5-h primed continuous intravenous infusion of 35S-Cys was conducted. ISS reduced plasma Cys and total SAA concentrations (16% and 21%, respectively; P < 0.05). However, ISS had no effect on the plasma concentrations of Tau and SO4, nor did it affect the appearance of 35S in plasma Tau, plasma SO4, urinary Tau, or urinary SO4 (P > 0.19). On a whole-body basis and including urinary excretion, ISS increased the appearance of 35S in Tau by 67% (P < 0.05), but tended to decrease the appearance of 35S in SO4 by 22% (P < 0.09). Overall, the current findings indicate that during ISS, decreased plasma SAA concentrations and increased plasma Cys flux are attributed in part to increased rates of Cys conversion to Tau, but not Cys catabolism to SO4. Thus, increased utilization of Cys for the synthesis of immune system metabolites, such as GSH and Tau, is likely the main contributor to increased Cys flux during ISS in pigs. In addition, the irreversible loss of Cys during ISS is small and has a minimal impact on the daily SAA requirements of starter pigs.

Effect of dietary fiber and threonine content on intestinal barrier function in pigs challenged with either systemic E. coli lipopolysaccharide or enteric Salmonella Typhimurium

Background

The independent and interactive effects of dietary fiber (DF) and threonine (Thr) were investigated in growing pigs challenged with either systemic E. coli lipopolysaccharide (LPS) or enteric Salmonella Typhimurium (ST) to characterise their effect on intestinal barrier function.

Results

In experiment 1, intestinal barrier function was assessed via oral lactulose and mannitol (L:M) gavage and fecal mucin analysis in pigs challenged with E. coli LPS and fed low fiber (LF) or high fiber (HF) diets with graded dietary Thr. Urinary lactulose recovery and L:M ratio increased (P < 0.05) during the LPS inoculation period in LF fed pigs but not in HF fed pigs. Fecal mucin output was increased (P < 0.05) in pigs fed HF compared to LF fed pigs. In experiment 2, RT-qPCR, ileal morphology, digesta volatile fatty acid (VFA) content, and fecal mucin output were measured in Salmonella Typhimurium challenged pigs, fed LF or HF diets with standard or supplemented dietary Thr. Salmonella inoculation increased (P < 0.05) fecal mucin output compared to the unchallenged period. Supplemental Thr increased fecal mucin output in the HF-fed pigs (Fib × Thr; P < 0.05). Feeding HF increased (P < 0.05) VFA concentration in cecum and colon. No effect of either Thr or fiber on expression of gene markers was observed except a tendency (P = 0.06) for increased MUC2 expression with the HF diet. Feeding HF increased goblet cell numbers (P < 0.05).

Conclusion

Dietary fiber appears to improve barrier function through increased mucin production capacity (i.e., goblet cell numbers, MUC2 gene expression) and secretion (i.e., fecal mucin output). The lack of effect of dietary Thr in Salmonella-challenged pigs provides further evidence that mucin secretion in the gut is conserved and, therefore, Thr may be limiting for growth under conditions of increased mucin production.

The effect of supplementing glycine and serine to a low crude protein diet on growth and skin collagen abundance of nursery pigs1

A total of 96 newly weaned barrows (initial body weight [BW]: 6.3 ± 0.5 kg) were used to determine the effect of a low crude protein (CP) diet supplemented with Gly and Ser on growth and skin collagen abundance. Barrows were assigned to one of three experimental diets in a three-phase feeding program fed for 35 days (n = 8; pen was the experimental unit): 1) corn-soybean meal diet (CON; 20.3% to 23.1% CP; as-fed, analyzed contents); 2) low CP diet (14.8% to 21.4% CP) supplemented with Gly and Ser (G + S) to the same concentrations as CON; 3) low CP diet supplemented with Glu to maintain the same CP concentration as the G + S diet (GLU; 15.0% to 22.1% CP). On days 21 and 35, eight pigs per treatment were euthanized for the determination of physical and chemical body composition and skin collagen abundance. Pigs fed the CON diet had greater overall ADG and final BW compared to pigs fed GLU and G + S (P < 0.01). Over the entire 35-day experimental period, ADFI was not influenced by dietary treatment but G:F tended to be greater for pigs fed CON than G + S (P = 0.084), while intermediate values were observed for GLU. Carcass weights on days 21 and 35 were greater for pigs fed CON than G + S or GLU (P < 0.01). Viscera weights on day 21 were greater for CON than G + S and GLU (P < 0.05) and on day 35 were greater for CON than G + S (P < 0.05) with intermediate values observed for GLU. The N intake (g/d) between days 0 and 35 was greater for CON than G + S or GLU (P < 0.05) and N retention in combined carcass and viscera was greater for CON than G + S (P < 0.01) with intermediate values observed for GLU. No treatment effects were observed for efficiency of N utilization. Between days 0 and 21 however, the efficiency of using dietary N for N retention in carcass and viscera tended to be less for pigs fed CON vs. GLU (73.8% vs. 91.6%), while intermediate values were observed for G + S (84.3%; P = 0.095). Pigs fed CON and G + S diets had greater skin collagen abundance than pigs fed GLU on days 21 and 35 (P < 0.01). Supplementing low CP diets with Glu or with Gly and Ser at the levels used in the current study did not maintain ADG or combined carcass and viscera N retention and only the G + S diet supported skin collagen abundance not different from pigs fed CON. The importance of meeting essential AA requirements for growth are well accepted, but supplementing specific NEAA may be needed when feeding reduced CP diets to newly weaned pigs to support secondary indicators of AA status, such as skin collagen abundance.

Bioavailability of valine in spray-dried L-valine biomass is not different from that in crystalline L-valine when fed to weanling pigs1

An experiment was conducted to test the hypothesis that Val from a spray dried L-Val fermentation biomass (Val-FB; 64.4% L-Val) has a bioavailability of 100% relative to Val from L-Val (98% L-Val) when fed to weanling pigs. A Val-deficient basal diet containing 0.63% standardized ileal digestible (SID) Val was formulated. Six additional diets were prepared by supplementing the basal diet with 0.08%, 0.17%, or 0.25% L-Val or 0.12%, 0.25%, or 0.37% Val-FB to create experimental diets from both Val sources that contained 0.71%, 0.79%, or 0.87% SID Val. Two hundred twenty-four weaned pigs (6.87 ± 0.64 kg initial BW) were allotted to a randomized complete block design with 7 diets, 4 pigs per pen, and 8 replicate pens per diet. Diets were fed for 20 d. At the conclusion of the experiment, a blood sample from 1 pig per pen was analyzed for blood urea nitrogen (BUN) and plasma free AA. A linear regression model was used to estimate the relative bioavailability (RBV) of Val in Val-FB relative to Val from L-Val. Results indicated that the final BW and ADG were greater (P < 0.01) for pigs fed diets supplemented with Val-FB than pigs fed diets supplemented with L-Val. The ADFI decreased (linear, P ≤ 0.01), whereas G:F increased (linear, P < 0.01) by increasing inclusion of both Val sources in the diets. Regardless of source of dietary Val, BUN values were reduced (linear and quadratic, P < 0.01) as the concentration of Val in the diet increased. Pigs fed diets supplemented with L-Val had increased (linear and quadratic, P ≤ 0.05) concentrations of Val and Arg in plasma, and plasma concentrations of Ile, Leu, Lys, Ala, Cys, and Pro linearly increased (P < 0.05). There was also an increase (linear, P < 0.05) in plasma concentrations of Ile, Leu, Met, Ala, Asp, Cys, and Pro as Val-FB was added to the diets, and the concentration of Val in plasma increased (linear and quadratic, P < 0.05). Using L-Val as the standard, the RBV of Val in Val-FB as determined by ADG, G:F, and final BW was 146%, 135%, and 143%, respectively, with 95% confidence intervals of 99% to 191%, 83% to 187%, and 70% to 217%, respectively. In conclusion, the linear regression estimated a RBV of at least 100% for Val in Val-FB relative to Val from L-Val, and pigs fed diet supplemented with Val-FB had greater final BW, ADG, and G:F than pigs fed diets supplemented with the same amount of Val from L-Val.

90 Effect of supplemental threonine on growth performance of pigs challenged with Salmonella typhimurium and fed high fiber diets

In a previous study, high dietary fiber (DF) and immune stimulation with systemic E. coli lipopolysaccharide independently, but not additively, increased the threonine (Thr) requirement for protein deposition. The current study investigated whether supplementing Thr to meet high DF and systemic immune challenge requirements would maintain performance of pigs exposed to an enteric immune challenge when fed high DF. A total of 128 pigs (22.6 ± 1.6 kg initial BW) were assigned to 1 of 4 dietary treatments (n = 8 pens/treatment; 4 pigs/pen) for 28 d. Treatments were low fiber (LF; 13% total DF) or high fiber (HF; 20% total DF) diets with standard (STD; 0.65% SID) or supplemental (SUP; 0.78% SID) Thr. After a 7-d adaptation, all pigs were orally inoculated with Salmonella typhimurium (2.3 × 109 CFU/ml). Blood samples and rectal swabs were obtained and rectal temperature recorded to determine clinical responses and Salmonella shedding. On d 7 post-inoculation, 1 pig/pen was euthanized and mesenteric lymph nodes, spleen and digesta (ileum, cecum, and colon) were sampled to assess Salmonella colonization and translocation. Body weight and feed intake were measured on d 0, 7, and 21 to calculate ADG, ADFI, and G:F. Rectal temperature increased (P &lt; 0.05) 24 h post-inoculation and remained elevated at d 6. Serum albumin concentration decreased (P &lt; 0.05), whereas haptoglobin concentration increased (P &lt; 0.05) post-inoculation. Fiber and Thr had no effect (P &gt; 0.05) on Salmonella count in ileum and cecum. Supplemental Thr increased (P &lt; 0.05) growth performance in LF- and HF-fed challenged pigs. However, performance of supplemented HF challenged pigs was less than (P &lt; 0.05) supplemented LF challenged pigs. These results suggest that Thr supplemented to meet requirements for high DF and systemic immune challenge was not sufficient to maintain growth performance of pigs fed HF diets and challenged with an enteric pathogen.

130 Comparison of amino acid digestibility in fish meal, porcine plasma, porcine red blood cell, and blood meal between broiler chickens and young pigs

The objective of this study was to compare the standardized ileal digestibility (SID) of AA in fish meal (FM), porcine plasma (PP), porcine red blood cell (RBC), and blood meal (BM) between broiler chickens and pigs. Five diets were prepared for both species including 4 diets containing test ingredients and a nitrogen-free diet. In Exp. 1, 416 male broiler chickens (initial BW = 705 ± 100.0 g) at d 18 post hatching were assigned to diets in a randomized complete block design with BW as a blocking factor. After 5 d of feeding, birds were euthanized for collection of ileal digesta. In Exp. 2, 10 barrows (initial BW = 22.1 ± 1.54 kg) surgically fitted with T-cannulas at the distal ileum were allotted to duplicate 5 × 4 incomplete Latin square design with 5 diets and 4 periods. Each experimental period consisted of 5-d adaptation and 2-d ileal digesta collection periods. Data for Exp. 1 and 2 were considered together as a 2 × 4 factorial arrangement with the effects of species (i.e., broiler chickens and pigs) and four diets (i.e., FM, PP, RBC, and BM). There were interactions (P &lt; 0.05) between species and diets on the SID of AA except for Pro. The SID of Lys, Met, Thr, and Trp in FM, PP, and RBC for broiler chickens were not different from values for pigs; however, the SID of respective AA in BM for broiler chickens were less than values for pigs. The SID of indispensable AA in BM were less than in FM, PP, or RBC within each species, but the SID of indispensable AA in BM for broiler chickens was less than values for pigs. In conclusion, utilization of AA in animal protein ingredients containing high concentration of CP varies between broiler chickens and pigs.

PSIX-26 Effect of supplemental Arg on respiration rate and body temperature of pigs exposed to heat stress

Heat stress (HS) reduces feed intake and affects the well-being of pigs by increasing their body temperature (BT) and respiration rate (RR). Nitric oxide, an Arg metabolite, helps to dissipate body heat by stimulating blood vasodilation. Because reduced feed intake translates into decreased Arg consumption, the effect of supplementing Arg in the diet on BT and RR was analyzed using 8-ileal cannulated pigs (61.7±2.7 kg BW) exposed to HS. A thermometer set to register BT at 5-min intervals was implanted into the ileum. There were two treatments: control wheat-soybean meal plus free Lys-Thr diet (CON), and the CON diet added with 0.20% free Arg (ARG). The study was conducted in two-6 d periods; d1-d3 for diet adaptation and d4-d6 for BT data analysis. The RR (respirations per min - rpm) was measured in all pigs at 0600-h and 1600-h. Pigs were fed at 0700-h and 1900-h, 900 g/meal. Ambient temperature and relative humidity were: 28.2-to-34.6 °C, 53-to-82%, respectively. Ambient temperature and BT followed a similar pattern every day. There was no interaction in BT and RR between periods. Overall, BT of ARG pigs (40.75°C) was slightly lower (P &lt; 0.05) than in CON pigs (40.71°C). Arg supplementation greatly reduced RR (rpm) regardless of period and day time (P &lt; 0.05): overall (91, 73), period-1 (98, 78), period-2 (85, 68), 0600-h, (68, 52), 1600-h (115, 94), respectively. The RR at 0600-h (60) was lower than at 1400-h (109; P &lt; 0.05) regardless of diet. The reduced RR because of Arg supplementation may be explained as an increased synthesis of nitric oxide probably resulting in both increased vasodilation and dissipation of body heat. In conclusion, although supplemental Arg caused a modest decrease in BT, the large RR reduction may indicate that Arg might help to improve the welfare of HS pigs.

PSVII-29 Validation of prediction equations for digestibility of energy and amino acids in commercial pigs using mini pigs

The objective was to validate the prediction equations for digestibility of gross energy and amino acids in commercial pigs using mini pigs. Five commercial crossbred barrows (Landrace × Yorkshire) with initial BW of 62.6 ± 6.1 kg and 5 mini pigs selected from Jeju Island native pigs (M-Pig; Cronex Co., Ltd., Hwaseong, Republic of Korea) with initial BW of 53.4 ± 7.4 kg were used. All pigs were fitted with a T-cannula at the distal ileum, and 5 animals of each breed were randomly allotted to a 5 × 10 Latin square design with 5 diets and 10 periods, respectively. A basal diet contained 98% corn and 4 experimental diets contained 20 or 40% rapeseed meal or wheat distillers dried grains with solubles at the expense of corn. Chromic oxide was included at 0.5% as an indigestible index. The accuracy of previously developed prediction equations for nutrient digestibility of commercial pigs was assessed by regressing measured values from commercial pigs minus predicted values from mini pigs on the predicted values centered to the mean. Comparison of measured and predicted apparent total tract digestibility of gross energy showed that the intercept (0.02 ± 0.81; P = 0.985) indicating mean bias and the slope (0.08 ± 0.15; P = 0.599) indicating linear bias were not different from 0. The equation for standardized ileal digestibility of lysine and arginine did not have mean bias or linear bias (P &gt; 0.05). However, the equations for standardized ileal digestibility of other amino acids had mean bias or linear bias (P &lt; 0.05). In conclusion, energy digestibility of commercial pigs may be predicted by previously developed prediction equations for commercial pigs using mini pigs.

PSVII-42 Growth performance, gut health, and immune responses of Escherichia coli-challenged weaned pigs fed probiotic-supplemented diets

To evaluate the effects of probiotics on performance and gut health of Escherichia coli-challenged weaned pigs, a total of 28 weaned pigs (initial BW = 8.25 kg) were housed individually in pens and fed 4 experimental diets for 21 d in a completely randomized design. The 4 diets were corn-soybean meal-based basal diet without or with 0.25% antibiotics (neomycin + oxytetracycline), 0.05% Bacillus subtilis DSM 32540, or 0.05% Bacillus pumilus DSM 32539. All pigs were orally challenged with K88 strain of E. coli on d 3. Feed intake and BW data, and blood samples were collected on d 3, 7, 14, and 21. Fecal scores were recorded daily. On d 21, pigs were sacrificed to determine gastrointestinal histomorphology, pH and organ weights. Supplementation of the basal diet with antibiotics or B. pumilus did not affect the overall (d 0 to 21) ADG and G:F. The B. subtilis supplementation did not affect the overall ADG, but tended to increase (P &lt; 0.1) the overall G:F by 15%. Fecal score was unaffected by dietary treatment. Supplementation of the basal diet with either probiotic, but not antibiotics increased (P &lt; 0.05) jejunal villous height and reduced (P &lt; 0.05) cecal digesta pH. Supplementation with B. pumilus tended to increase (P &lt; 0.1) colon weight relative to BW; however, antibiotics or B. subtilis supplementation did not affect colon weight. The addition of B. subtilis to basal diet tended to increase (P &lt; 0.1) serum immunoglobulin A concentration on d 21 of the study; however, such effect was not observed with the addition of antibiotics or B. pumilus. In conclusion, dietary B. subtilis improved G:F and jejunal villous height and reduced cecal digesta pH, indicating that dietary supplementation with B. subtilis at 0.05% could improve growth performance and gut health of weaned pigs.

Efficiency of utilizing standardized ileal digestible lysine and threonine for whole-body protein retention in pregnant gilts during early, mid-, and late gestation1

Two experiments were conducted to determine the efficiency of utilizing SID Lys and Thr for whole-body protein retention (kSIDLys and kSIDThr) in pregnant gilts. In Exp. 1, 45 gilts (158.0 ± 8.0 kg at day 39.4 ± 1 of gestation) in 2 groups were used in a 3-period nitrogen (N)-balance study. Gilts were assigned to 1 of 4 diets set to provide 60, 70, 80, and 90% of predicted daily SID Lys requirement for protein retention (NRC, 2012) in each of early (day 41 to 52, 10.44 g/d), mid- (day 68 to 79, 9.60 g/d), and late gestation (day 96 to 107, 16.04 g/d). Diets contained 3,300 kcal ME/kg and 11.6% CP; given at a rate of 2.13 kg/d in early and mid-gestation and at 2.53 kg/d during late gestation. The 12-d balance period (7-d adaptation; 5-d urine and fecal collection) was based on total urine collection using urinary catheters and determination of fecal N digestibility using indigestible marker. The SID Lys required for whole-body protein retention was estimated using the NRC (2012) model and the predicted Lys content of each gestation pool. Lysine efficiency at each diet Lys level was calculated as the ratio of daily Lys retention and SID Lys intake. The linear and quadratic response in whole-body N and Lys retention and Lys efficiency for each balance period was determined. The kSIDLys was determined from the slope generated by regressing whole-body Lys retention vs. SID Lys intake, with y-intercept set to 0. In Exp. 2, 45 gilts (165.7 ± 13.6 kg at day 39.1 ± 2 of gestation) were assigned to 1 of 4 diets set to provide 60, 70, 80, and 90% of the predicted daily SID Thr requirement for protein retention in each of early (6.46 g/d), mid- (6.05 g/d), and late gestation (9.75 g/d). Animal management, N-balance procedure, data collection and calculation, and statistical analyses were patterned from Exp. 1. In early and mid-gestation, whole-body N retention, as well as Lys and Thr retention, was not affected by the dietary SID Lys and Thr. In late gestation, there was a linear increase (P < 0.001) in whole-body N, Lys and Thr retention. The kSIDLys and kSIDThr in late gestation were determined to be 0.54. The lack of response in whole-body protein retention in early and mid-gestation may in partly reflect excess Lys and Thr intake. Lysine and Thr efficiency calculated at the lowest dietary Lys and Thr was 0.49 and 0.32 in early gestation and 0.61 and 0.52 in mid-gestation, respectively. Based on the available evidence, kSIDLys and kSIDThr do not appear to be constant throughout gestation.