Nitrogen balance in barrows fed low-protein diets supplemented with essential amino acids

Recombinant Phytase Modulates Blood Amino Acids and Proteomics Profiles in Pigs Fed with Low-Protein, -Calcium, and -Phosphorous Diets

A beneficial effect of corn-expressed phytase (CEP) on the growth performance of pigs fed with very low-protein (VLP) diets was previously shown. Little is known whether this improvement is related to alterations in the expression profiles of blood proteins and amino acids (AAs). The objective of this study was to investigate whether supplementation of VLP, low-calcium (Ca), and low-P diets with a CEP would alter the blood AAs and protein expression profiles in pigs. Forty-eight pigs were subjected to one of the following groups (n = 8/group) for 4 weeks: positive control (PC), negative control-reduced protein (NC), NC + low-dose CEP (LD), NC + high-dose CEP (HD), LD with reduced Ca/P (LDR), and HD with reduced Ca/P (HDR). Plasma leucine and phenylalanine concentrations were reduced in NC; however, the LD diet recovered the concentration of these AAs. Serum proteomics analysis revealed that proteins involved with growth regulation, such as selenoprotein P were upregulated while the IGF-binding proteins family proteins were differentially expressed in CEP-supplemented groups. Furthermore, a positive correlation was detected between growth and abundance of proteins involved in bone mineralization and muscle structure development. Taken together, CEP improved the blood profile of some essential AAs and affected the expression of proteins involved in the regulation of growth.

Dietary Isoleucine and Valine: Effects on Lipid Metabolism and Ureagenesis in Pigs Fed with Protein Restricted Diets

A mixture of valine (Val) and isoleucine (Ile) not only decreases the negative impact of very low protein (VLP) diets on the growth of pigs, but also influences the nitrogen (N) balance and lipid metabolism; however, the underlying pathways are not well understood. This study aimed to investigate the effect of dietary Val and Ile on lipogenesis, lipolysis, and ureagenesis under protein restriction. After one week of acclimation, forty three-week-old pigs were randomly assigned to following dietary treatments (n = 8/group) for 5 weeks: positive control (PC): normal protein diet; negative control (NC): VLP diet; HV: NC supplemented with Val; HI: NC supplemented with Ile; and HVI: NC supplemented with both Val and Ile. HVI partially improved the body weight and completely recovered the feed intake (FI) of pigs fed with NC. HVI increased thermal radiation and improved the glucose clearance. HVI had a lower blood triglyceride than PC and blood urea N than NC. NC and HV promoted lipogenesis by increasing the transcript of fatty acid synthase (FAS) in the liver and lipoprotein lipase (LPL) in adipose tissue but reducing hormone-sensitive lipase (HSL) in the liver. HVI reduced the increased rate of lipogenesis induced by the NC group through normalizing the mRNA abundance of hepatic FAS, sterol regulatory element binding transcription factor 1, and HSL and LPL in adipose tissue. NC, HV, HI, and HVI reduced the ureagenesis by decreasing the protein abundance of carbamoyl phosphate synthetase I, ornithine transcarboxylase, and arginosuccinate lyase in the liver. Overall, HVI improved the growth, FI, and glucose clearance, and decreased the rate of lipogenesis induced by VLP diets.

Effect of Isoleucine and Added Valine on Performance, Nutrients Digestibility and Gut Microbiota Composition of Pigs Fed with Very Low Protein Diets

Little is known whether a combination Ile and added Val improves the growth of pigs offered very low protein (VLP) diets through changes in nutrients digestibility and gut microbiota. The objective of this study was to investigate the effect of a mixture of Val above and Ile at NRC levels on growth, nutrient digestibility and gut microbiota in pigs fed with VLP diets. Forty, weaned piglets were assigned to: positive control: normal-protein-diet; negative control (NC): VLP diet supplemented with first four limiting amino acids; VA: NC with Val above NRC; IL: NC with Ile at NRC level; VAIL: NC with Val above and Ile at NRC levels. While both VAIL and VA groups completely recovered the inhibitory effects of VLP diets on feed intake, only VAIL partially recovered the negative effects of VLP diets on growth performance. VAIL and VA increased the thermal radiation and decreased the digestibility of nitrogen. NC increased the relative abundance of Pasteurellaceae and Enterobacteriaceae in the colon. VAIL had a higher abundance of colonic Actinobacteria, Enterococcus, and Brevibacillus and the colon content of VA was more enriched with Mogibacterium. Overall, VAIL partially improved the growth performance which is likely linked with alterations in gut microbiota composition.

Dietary branched-chain amino acids modulate the dynamics of calcium absorption and reabsorption in protein-restricted pigs

Background

Very low-protein (VLP) diets negatively impact calcium (Ca) metabolism and absorption. The objective of this study was to investigate the effect of supplemental branched-chain amino acids (BCAA) and limiting amino acids (LAA) on Ca digestibility, absorption and reabsorption in pigs fed with VLP diets. Forty-eight piglets were assigned to six treatments: positive control (PC), negative control (NC), and NC containing LAA 25%, LAA 50%, LAA + BCAA 25% (LB25) and LAA + BCAA 50% (LB50) more than recommendations.

Results

Relative to PC or NC, LB25 and LB50 had higher digestibility of Ca and plasma Ca and phosphorus (P), but lower plasma vitamin D₃. LB50 tended to increase vitamin D receptor transcript and protein in the gut, but decreased mRNA or protein abundance of parathyroid hormone 1 receptor (PTH1R), calbindin 1 (CALB1), cytochrome P450 family 27 subfamily B member 1 and occludin in small intestine. LB50 increased the transcript of cytochrome P450 family 24 subfamily A member 1 and PTH1R but decreased the transcript of transient receptor potential cation channel subfamily V member 5, CALB1 and solute carrier family 17 member 4 in kidney.

Conclusion

Overall, BCAA increased Ca digestibility through regulating the transcellular and paracellular Ca absorption in the gut and reabsorption in kidney during protein restriction.

Effects of Different Methionine Levels in Low Protein Diets on Production Performance, Reproductive System, Metabolism, and Gut Microbiota in Laying Hens

This study investigated the effects of different levels of methionine (Met) in a low protein diet on the production performance, reproductive system, metabolism, and gut microbial composition of laying hens to reveal the underlying molecular mechanism of Met in a low protein diet on the host metabolism and gut microbial composition and function of hens. A total of 360 healthy 38-week-old Peking Pink laying hens with similar body conditions and egg production (EP) were randomly divided into four groups with nine replicates per treatment and 10 hens per replicate. The hens in each treatment group were fed low protein diets containing different levels of Met (0.25, 0.31, 0.38, and 0.47%, respectively) for 12 weeks. Feed and water were provided ad libitum throughout the trial period. The results showed that, compared with the 0.25% Met group, the final body weight (FBW), average daily gain (ADG), EP, egg weight (EW), and average daily feed intake (ADFI) in the other groups were significantly increased and feed egg ratio (FER) was decreased. Meanwhile, the EW and yield of abdominal fat (AFY) in the 0.47% Met group were higher than those in other groups. The triglyceride (TG), estradiol (E2), total protein (TP), albumin (ALB), and immunoglobulin A (IgA) in the 0.38 and 0.47% Met groups were higher than those in other groups. In addition, 16S rRNA gene sequencing revealed that there was no difference in the Sobs index, ACE index, and Shannon index among all groups. However, it is worth noting that feeding low protein diets with Met changed the gut microbial composition (e.g., the supplementation of Met increased the level of Lactobacillus and decreased the proportion of Faecalibacterium). Also, our results showed that the changes in gut microbial composition induced by the diets with different levels of Met were closely related to the changes of key parameters: ADFI, EW, FBW, TG, EM, EP, ADG, FER, and uric acid (UA). Our results highlight the role of adding an appropriate amount of Met to the low protein diet in laying hens, which could improve the gut microbial composition, production performance, reproductive system, and nutrient metabolism of laying hens. In conclusion, this study suggested that when the Met level was 0.38%, the production performance of the laying hens was pretty good.

Low crude protein diets supplemented with casein hydrolysate enhance the intestinal barrier function and decrease the pro-inflammatory cytokine expression in the small intestine of pigs

To reduce nitrogen excretion and lower feeding costs, low crude protein (CP) diets are sometimes proposed, however, a great reduction of dietary CP concentration (>4% reduction vs. recommended concentration), even supplemented with essential and nonessential amino acids (AA) can detrimentally affect small intestinal barrier function and immunity, possibly due to the excessive lack of peptides. Here we hypothesize that with an extremely low CP concentration diet, protein-derived peptides, rather than AA supplementation, can improve intestinal barrier development and health. To test this hypothesis, 21 growing pigs (19.90 ± 1.00 kg body weight) were randomly assigned to 3 treatments with control diet (16% CP), or low CP diets (13% CP) supplemented with AA (LCPA) or casein hydrolysate (LCPC) for 28 days. In comparison with the control diet, the LCPA diet decreased the protein expression level of jejunal barrier factor zonula occludens-1 (ZO-1) and stem cell proliferation factor leucine-rich repeat-containing G-protein-coupled receptor-5, whereas the LCPC diet enhanced intestinal barrier function by increasing the protein expression level of jejunal occludin and ZO-1 and ileal mucin-2. The LCPA diet reduced Lactobacillus counts, whereas the LCPC diet increased Lactobacillus counts and reduced Escherichia coli counts in the ileum. The LCPA diet also increased protein expression levels of pro-inflammatory cytokine interleukin-6 (IL-6) and IL-22, whereas the LCPC diet decreased protein expression levels of pro-inflammatory IL-1β, IL-17A and tumor necrosis factor-α in the ileum. Collectively, the casein hydrolysate supplementation of low CP diets showed beneficial effects on the small intestinal barrier, bacterial community, and immunity in pigs, pointing to the important role of protein-derived peptides in small intestinal health in cases of low crude protein diets.

Branched-chain amino acids partially recover the reduced growth of pigs fed with protein-restricted diets through both central and peripheral factors

The objective of this study was to assess the growth efficiency of pigs fed with protein-restricted diets supplemented with branched-chain amino acids (BCAA) and limiting amino acids (LAA) above the recommended levels. Following 2 weeks of adaptation, 48 young barrows were weight matched and randomly assigned to 6 treatments (8 pigs/treatment) for 4 weeks: positive control (PC) with standard protein, negative control (NC) with very low protein containing LAA (i.e., Lys, Met, Thr and Trp) at recommended levels, and NC containing LAA 25% (L25), LAA 50% (L50), LAA+BCAA (i.e., Leu, Ile and Val) 25% (LB25) and LAA+BCAA 50% (LB50) more than recommendations. Feed intake (FI) and body weight (BW) were measured daily and weekly, respectively. At week 6, blood samples were collected, all pigs euthanized and tissue samples collected. The data were analyzed by univariate GLM or mixed procedure (SPSS) and the means were separated using paired Student's t-test followed by Benjamini-Hochberg correction. Relative to PC, NC had decreased FI, BW, unsupplemented plasma essential amino acids, serum insulin-like growth factor-I (IGF-I) and hypothalamic neuropeptide Y (NPY) (P < 0.01). Compared to NC, L25 or L50, LB50 had increased BW and serum IGF-I and decreased plasma serotonin and both LB25 and LB50 had higher FI, plasma BCAA, hypothalamic 5-hydroxytryptamine-receptor 2A and NPY and jejunal 5-hydroxytryptamine-receptor 7 (P < 0.01). Overall, supplementation of protein-restricted diets with increased levels of dietary BCAA partially recovered the negative effects of these diets on growth through improved IGF-I concentration and FI, which was associated with changed expression of serotonin receptors, blood AA and hypothalamic NPY.

A Novel Corn-Expressed Phytase Improves Daily Weight Gain, Protein Efficiency Ratio and Nutrients Digestibility and Alters Fecal Microbiota in Pigs Fed with Very Low Protein Diets

The objective of this study was to assess the effect of a novel corn-expressed phytase (CEP) on growth, nutrients digestibility, bone characteristics and fecal microbiota of pigs fed with very low-protein, -calcium (Ca) and -phosphorous (P) diets. Forty-eight barrows were subjected to 6 groups for 4 weeks: positive control-adequate protein (PC), negative control-reduced protein (NC), NC + low-dose CEP, i.e., 2000 FTU/kg (LD), NC + high-dose CEP, i.e., 4000 FTU/kg (HD), LD with 0.12% unit reduced Ca and 0.15% unit reduced available P (LDR), and HD with 0.12% unit reduced Ca and 0.15% unit reduced available P (HDR). Compared to NC, LD and HDR had a higher average daily gain (ADG) and gain:protein ratio (G:P), HD and HDR had greater apparent fecal digestibility of Ca and P and bone mineral density and LDR and HDR had lower serum osteocalcin. The feces of LD was enriched in Lachnospiraceae, while the HD had a higher abundance of Succinvibrio and LDR had a higher abundance of Bifidobacterium and Actinobacteria. In conclusion, supplementation of protein-restricted diets with a CEP decreased their negative effects on ADG and G:P ratio, increased the digestibility of Ca and P regardless of the levels of these minerals in the diet, improved bone characteristics and produced differential effects on fecal bacterial population.

Effects of different levels of crude protein and protease on nitrogen utilization, nutrient digestibility, and growth performance in growing pigs

This study was conducted to evaluate the effects of different levels of crude protein (CP) and protease on nitrogen (N) utilization, nutrient digestibility, and growth performance in growing pigs. A total of six crossbred ([Landrace × Yorkshire] × Duroc) barrows were individually accepted in 1.2 m × 0.7 m × 0.96 m stainless steel metabolism cages. The pigs (average initial body weight of 27.91 ± 1.84 kg) randomly assigned to six diets with six weeks (6 × 6 Latin square design). The experiment was carried out in an environment with a temperature of 23 ± 1.5°C, a relative humidity of 83 ± 2.3% and a wind speed of 0.25 ± 0.03 m/s. The dietary treatments were arranged in a 2 × 3 factorial design with two levels of CP (15.3% or 17.1%) and three levels of protease (0 ppm, 150 ppm, or 300 ppm). The average daily gain and gain to feed ratio (G:F) tended to increase (p = 0.074) with increasing amounts of protease. The low CP level diet reduced (p < 0.050) urinary and fecal N concentrations, the total N excretion in feces, and increased (p < 0.050) N retention. Different protease levels in the diet did not affect (p > 0.05) at N intake, but supplementation of the diets with 300 ppm protease decreased (p < 0.050) the N concentration in urine and feces and tended to increase (p = 0.061) the percentage of N retention retained of the total N intake. The dietary CP level did not affect (p > 0.050) the apparent total tract digestibility (ATTD) of dry matter, digestible energy (DE), and metabolic energy (ME), but diet supplementation with 300 ppm protease showed higher (p < 0.050) ATTD of DE and ME than in the protease-free diet. Therefore, a low protein diet with protease could improve the utilization of nitrogen, thereby reducing the negative effect of N excretion into the environment while maintaining or increasing growth performance compared to a high protein diet.

Effect of very low-protein diets supplemented with branched-chain amino acids on energy balance, plasma metabolomics and fecal microbiome of pigs

Feeding pigs with very-low protein (VLP) diets while supplemented with limiting amino acids (AA) results in decreased growth. The objective of this study was to determine if supplementing VLP diets with branched-chain AA (BCAA) would reverse the negative effects of these diets on growth and whether this is associated with alterations in energy balance, blood metabolomics and fecal microbiota composition. Twenty-four nursery pigs were weight-matched, individually housed and allotted into following treatments (n = 8/group): control (CON), low protein (LP) and LP supplemented with BCAA (LP + BCAA) for 4 weeks. Relative to CON, pigs fed with LP had lower feed intake (FI) and body weight (BW) throughout the study, but those fed with LP + BCAA improved overall FI computed for 4 weeks, tended to increase the overall average daily gain, delayed the FI and BW depression for ~ 2 weeks and had transiently higher energy expenditure. Feeding pigs with LP + BCAA impacted the phenylalanine and protein metabolism and fatty acids synthesis pathways. Compared to CON, the LP + BCAA group had higher abundance of Paludibacteraceae and Synergistaceae and reduced populations of Streptococcaceae, Oxyphotobacteria_unclassified, Pseudomonadaceae and Shewanellaceae in their feces. Thus, supplementing VLP diets with BCAA temporarily annuls the adverse effects of these diets on growth, which is linked with alterations in energy balance and metabolic and gut microbiome profile.

Low Protein-High Carbohydrate Diets Alter Energy Balance, Gut Microbiota Composition and Blood Metabolomics Profile in Young Pigs

Reducing dietary crude protein (CP) beyond a certain threshold leads to poor growth performance in pigs; however, the underlying mechanisms are not well understood. Following an adaption period, thirty-seven weaned pigs were weight matched (8.41 ± 0.14 kg), housed individually and randomly assigned into three groups with different dietary CP levels: 24% CP (CON; n = 12), 18% CP (n = 12) and 12% CP (n = 13) for 28 days. The body weight was not different between the CON and 18% CP diets, but 12% CP significantly decreased body weight after day 21. Compared to the CON, pigs fed with 12% CP decreased feed intake day 17 onwards. The 12% CP diet increased the energy expenditure during week 1 compared to the CON. The 12% CP influenced starch and sucrose, nitrogen, and branched-chain amino acids metabolism pathways. The feces of pigs fed with 12% CP were less enriched in Prevotella, but had higher relative abundance of Christensenedilaceae, Aligiphilus and Algoriphagus than CON and 18% CP. Overall, reducing dietary CP by 50%, but not by 25%, significantly influenced the physiological responses in nursery pigs. The pigs fed with low or standard protein diets had differential bacterial communities in their feces as well as serum metabolomics profile.

Effect of different dietary protein levels and amino acids supplementation patterns on growth performance, carcass characteristics and nitrogen excretion in growing-finishing pigs

Background

This study was conducted to determine the effects of different dietary protein levels and amino acids supplementation patterns in low protein diets on the growth performance, carcass characteristics and nitrogen excretion in growing-finishing pigs.

Forty-two barrows (25.00 ± 0.39 kg) were randomly assigned to 7 diets. Diet 1: the high crude protein diet with balanced for 10 essential amino acids (EAAs). Diet 2: the medium crude protein diet with 2% (approx) decreased protein level of Diet 1 and balanced 10 EAAs. Diet 3: the low crude protein diet with 4% decreased protein level of Diet 1 and balanced 10 EAAs. The protein levels of Diet 4, 5, 6 and 7 were the same as that of Diet 3. Diet 4 was only balanced for lysine (Lys), methionine (Met), threonine (Thr) and tryptophan (Trp); Diet 5 and 6 were further supplemented with extra isoleucine (Ile) or valine (Val), respectively; Diet 7 was further supplemented with extra Ile + Val.

Results

Over the 112 days trial, the reduction of dietary protein by 2% or 4% with balanced10 EAAs significantly decreased nitrogen excretion (P <  0.05), but had no effects on growth performance and carcass characteristics (P > 0.05). In low protein diet, Val supplementation significantly increased body weight gain at 25–50 kg phase (P <  0.05), while Ile supplementation at 75–100 kg phase and 100–125 kg phase significantly reduced the ratio of feed to gain (P <  0.05). No effect of different dietary protein levels and amino acids supplementation patterns in low protein diets on carcass characteristics was observed (P > 0.05). The total N excretion of pigs supplemented with only Lys, Met, Thr and Trp was numerically higher than that of pigs fed with extra Ile, or Val, or Ile + Val diets.

Conclusion

In low protein diet, Val is more required than Ile in the early growing phage (25–50 kg), while Ile becomes more required in the late growing and finishing phage (75–125 kg).

Electronic supplementary material

The online version of this article (10.1186/s40104-019-0381-2) contains supplementary material, which is available to authorized users.

Advances in low-protein diets for swine

Recent years have witnessed the great advantages of reducing dietary crude protein (CP) with free amino acids (AA) supplementation for sustainable swine industry, including saving protein ingredients, reducing nitrogen excretion, feed costs and the risk of gut disorders without impairing growth performance compared to traditional diets. However, a tendency toward increased fatness is a matter of concern when pigs are fed low-protein (LP) diets. In response, the use of the net energy system and balanced AA for formulation of LP diets has been proposed as a solution. Moreover, the extent to which dietary CP can be reduced is complicated. Meanwhile, the requirements for the first five limiting AA (lysine, threonine, sulfur-containing AA, tryptophan, and valine) that growing-finishing pigs fed LP diets were higher than pigs fed traditional diets, because the need for nitrogen for endogenous synthesis of non-essential AA to support protein synthesis may be increased when dietary CP is lowered. Overall, to address these concerns and give a better understanding of this nutritional strategy, this paper reviews recent advances in the study of LP diets for swine and provides some insights into future research directions.

The addition of protein-bound amino acids in low-protein diets improves the metabolic and immunological characteristics in fifteen- to thirty-five-kg pigs

This study was to evaluate the effects of supplementation of AA form (crystalline vs. protein bound) in low-protein diets on growth, metabolic, and immunological characteristics of pigs. A total of 80 barrows (PIC 327 × 1050; 15.57 ± 0.13 kg BW and 48 ± 2 d of age), housed in 4 pigs per pen with 5 pens per treatment, were assigned to 4 dietary treatments of 17, 15, and 13% CP and 13% CP plus casein for 28 d. The crystalline AA were supplemented to meet the requirement of indispensable AA in pigs. Results showed that pigs fed the 13% CP diet or the 13% CP plus casein diet had lower ( < 0.01) ADG and ADFI and a greater ( < 0.01) feed:gain ratio than pigs fed the 17% CP or 15% CP diets over the 4-wk study period. Compared with other diets, pigs fed the 13% CP diet had decreased concentrations of plasma urea nitrogen, albumin ( < 0.01), and mRNA expressions of Toll-like receptor 4 (), nuclear factor kappa B (; < 0.05), and Toll-interacting protein (; < 0.01) in the ileum and also increased activity of plasma glutamate-pyruvate transaminase ( < 0.05) and concentrations of IL-1β ( < 0.05) and tumor necrosis factor-α ( < 0.01); however, these characteristics were partly normalized by feeding the 13% CP plus casein diet. Furthermore, the plasma concentration of insulin-like growth factor 1 (IGF-1; < 0.01) and mRNA expressions of protein kinase B (), mammalian target of rapamycin (), and ribosomal protein S6 kinase () in longissimus muscle were increased ( < 0.05) in pigs fed the 13% CP plus casein diet relative to pigs fed the 17% CP or 15% CP diets. In summary, reducing dietary CP level from 17% to 15% had no effect on growth, metabolic, and immunological characteristics of 15- to 35-kg pigs. A further reduction of dietary CP level up to 13% would lead to poor growth performance, but metabolic and immunological characteristics were partly normalized using protein-bound AA to replace synthesized AA in the 13% CP diet.

Environmental Sustainability Analysis and Nutritional Strategies of Animal Production in China

Animal production in China has achieved considerable progress and contributes to 46% of the total agriculture output value of the country. However, this fast expansion of animal production has led to environmental pollution. In this article, we review the status of soil, water, and air pollution associated with animal production in China and analyze the main sources of the pollutants. The government has promulgated regulations and standards, and effective models and technologies have been developed to control pollution during the last 10 years. Because nutrition and feed strategies represent the most effective method of controlling environmental pollution at the source, this review focuses on nutritional technologies, including accurate feed formulation, rational use of additives, and proper processing of feeds. The advances of modern biotechnology and big data systems also provide more modern approaches to decreasing wastage release. These nutritional strategies are expected to promote sustainable development of animal production.

Effects of low-protein diets supplemented with indispensable amino acids on growth performance, intestinal morphology and immunological parameters in 13 to 35 kg pigs

The objective of this study was to determine if a moderate or high reduction of dietary CP, supplemented with indispensable amino acids (IAA), would affect growth, intestinal morphology and immunological parameters of pigs. A total of 40 barrows (initial BW=13.50±0.50 kg, 45±2 day of age) were used in a completely randomized block design, and allocated to four dietary treatments containing CP levels at 20.00%, 17.16%, 15.30% and 13.90%, respectively. Industrial AA were added to meet the IAA requirements of pigs. After 4-week feeding, blood and tissue samples were obtained from pigs. The results showed that reducing dietary CP level decreased average daily gain, plasma urea nitrogen concentration and relative organ weights of liver and pancreas (P<0.01), and increased feed conversion ratio (P<0.01). Pigs fed the 13.90% CP diet had significantly lower growth performance than that of pigs fed higher CP at 20.00%, 17.16% or 15.30%. Moreover, reducing dietary CP level decreased villous height in duodenum (P<0.01) and crypt depth in duodenum, jejunum and ileum (P<0.01). The reduction in the dietary CP level increased plasma concentrations of methionine, alanine (P<0.01) and lysine (P<0.05), and decreased arginine (P<0.05). Intriguingly, reducing dietary CP level from 20.00% to 13.90% resulted in a significant decrease in plasma concentration of IgG (P<0.05), percentage of CD3+T cells of the peripheral blood (P<0.01), also down-regulated the mRNA abundance of innate immunity-related genes on toll-like receptor 4, myeloid differentiation factor 88 (P<0.01) and nuclear factor kappa B (P<0.05) in the ileum. These results indicate that reducing dietary CP level from 20.00% to 15.30%, supplemented with IAA, had no significant effect on growth performance and had a limited effect on immunological parameters. However, a further reduction of dietary CP level up to 13.90% would lead to poor growth performance and organ development, associated with the modifications of intestinal morphology and immune function.

Reduced dietary protein level influences the free amino acid and gene expression profiles of selected amino acid transceptors in skeletal muscle of growing pigs

This study was conducted to evaluate the effect of reduced dietary protein level on growth performance, muscle mass weight, free amino acids (FAA) and gene expression profile of selected amino acid transceptors in different fibre type of skeletal muscle tissues (longissimus dorsi, psoas major, biceps femoris) of growing pigs. A total of 18 cross-bred growing pigs (Large White × Landrace × Duroc) with initial body weight (9.57 ± 0.67 kg) were assigned into three dietary treatments: 20% crude protein (CP) diet (normal recommended, NP), 17% CP diet (low protein, LP) and 14% CP diet (very low protein, VLP). The results indicated improved feed-to-gain ratio was obtained for pigs fed LP and NP diets (p < 0.01), while the pigs fed VLP diet showed the worst growth performance (p < 0.01). There was no significant difference in the weights of longissimus dorsi and psoas major muscle between LP and NP groups (p > 0.05). Majority of the determined FAA concentration of LP group were greater than or equal to those of NP group in both longissimus dorsi and psoas major muscle (p < 0.01). Further, the mRNA expression levels of sodium-coupled neutral amino acid transceptor 2, L-type amino acid transceptor 1 and proton-assisted amino acid transceptors 2 were higher in skeletal muscle tissue in LP group compared to those of the pigs fed NP or VLP diet. These results suggested that reduced dietary protein level (3 points of percentage less than recommended level) would upregulate the mRNA expression of amino acid transceptors to enhance the absorption of FAA in skeletal muscle of growing pigs. There seems to be a relationship between response of AA transceptors to the dietary protein level in skeletal muscle tissue of different fibre type. To illustrate the underlying mechanisms will be beneficial to animal nutrition.

Effects of reducing dietary protein on the expression of nutrition sensing genes (amino acid transporters) in weaned piglets

The effects of crude protein (CP) levels in the diet on the mRNA expression of amino acid (AA) transporters were studied in a 45-d trial. Eighteen piglets with an initial body weight (BW) of 9.57 kg were assigned to three groups (14%, 17%, and 20% CP in the diet) in a completely randomized design (six replicates per treatment). Diets were supplemented with crystalline AA to achieve equal standardized ileal digestible contents of Lys, Met plus Cys, Thr, and Trp, and were provided ad libitum. After 45 d, all piglets were slaughtered to collect small intestine samples. Compared with the values in the 14% CP group, the expressions of ASCT2, 4F2hc, and ATB(0) mRNA in the jejunum were increased by 23.00%, 12.00%, 6.00% and 48.00%, 47.00%, 56.00% in the 17% and 20% CP groups, respectively. These results indicate that a 14% CP diet supplemented with crystalline AA may not transport enough AA into the body and maintain growth performance of piglets. However, a reduction of dietary 17% CP may reduce the excretion of nitrogen into the environment while supporting the development of piglets. Therefore, the 17% CP level is more suitable than 14% CP level.

Effects of Dietary Crude Protein Levels and Cysteamine Supplementation on Protein Synthetic and Degradative Signaling in Skeletal Muscle of Finishing Pigs

Dietary protein levels and cysteamine (CS) supplementation can affect growth performance and protein metabolism of pigs. However, the influence of dietary protein intake on the growth response of CS-treated pigs is unclear, and the mechanisms involved in protein metabolism remain unknown. Hence, we investigated the interactions between dietary protein levels and CS supplementation and the effects of dietary crude protein levels and CS supplementation on protein synthetic and degradative signaling in skeletal muscle of finishing pigs. One hundred twenty barrows (65.84 ± 0.61 kg) were allocated to a 2 × 2 factorial arrangement with five replicates of six pigs each. The primary variations were dietary crude protein (CP) levels (14% or 10%) and CS supplemental levels (0 or 700 mg/kg). The low-protein (LP) diets (10% CP) were supplemented with enough essential amino acids (EAA) to meet the NRC AA requirements of pigs and maintain the balanced supply of eight EAA including lysine, methionine, threonine, tryptophan, valine, phenylalanine, isoleucine, and leucine. After 41 days, 10 pigs per treatment were slaughtered. We found that LP diets supplemented with EAA resulted in decreased concentrations of plasma somatostatin (SS) (P<0.01) and plasma urea nitrogen (PUN) (P<0.001), while dietary protein levels did not affect other traits. However, CS supplementation increased the average daily gain (P<0.001) and lean percentage (P<0.05), and decreased the feed conversion ratio (P<0.05) and back fat (P<0.05). CS supplementation also increased the concentrations of plasma insulin-like growth factor 1 (IGF-1) (P<0.001), and reduced the concentrations of leptin, SS, and PUN (P<0.001). Increased mRNA abundance of Akt1 and IGF-1 signaling (P<0.001) and decreased mRNA abundance of Forkhead Box O (FOXO) 4 (P<0.01) and muscle atrophy F-box (P<0.001) were observed in pigs receiving CS. Additionally, CS supplementation increased the protein levels for the phosphorylated mammalian target of rapamycin (mTOR), eIF-4E binding protein 1, and ribosomal protein S6 kinase 1 (P<0.001). There were no interactions between dietary protein levels and CS supplementation for all traits. In conclusion, dietary protein levels and CS supplementation influenced growth and protein metabolism through independent mechanisms in pigs. In addition, LP diets supplemented with EAA did not affect growth performance and other traits except the concentrations of SS and PUN probably through maintenance of protein synthesis and degradation signaling. Moreover, CS supplementation improved growth performance by increasing plasma IGF-1 concentrations possibly through alterations of mTOR and Akt/FOXO signaling pathways in skeletal muscle of finishing pigs.

Co-dependence of genotype and dietary protein intake to affect expression on amino acid/peptide transporters in porcine skeletal muscle

A total of 96 barrows (48 pure-bred Bama mini-pigs representing fatty genotype, and 48 Landrace pigs representing lean genotype) were randomly assigned to either a low- or adequate-protein treatment diet. The experimental period commenced at 5 weeks of age and extended to the finishing period. After euthanasia, blood and skeletal muscle samples were collected from pigs at the nursery, growing, and finishing phases. Our results indicate that the concentrations of free AAs in the plasma and muscle decreased as the age of the pigs increased. In addition, a strain × growth phase interaction (P < 0.05) was observed for the free AA pool in the plasma and muscle. The low-protein diet upregulated (P < 0.05) the mRNA levels for T1R1/T1R3 involved in glutamate binding, but downregulated (P < 0.05) the mRNA levels for PAT1, PAT2, and ASCT2, which transport neutral AAs into muscles. Bama mini-pigs had higher (P < 0.05) mRNA levels for LAT1, SNAT2, and EAAC1, but a lower (P < 0.05) mRNA level for PepT1, compared with Landrace pigs. Collectively, our findings indicate that adequate provision of dietary protein plays an important role in regulating profiles of free AA pools and expression of key AA/peptide transporters/transceptors in a genotype- and tissue-specific manner.

Estimation of the optimal ratio of standardized ileal digestible threonine to lysine for finishing barrows fed low crude protein diets

Two experiments were conducted to determine the standardized ileal digestible (SID) lysine (Lys) requirement and the ideal SID threonine (Thr) to Lys ratio for finishing barrows. In Exp. 1, 120 barrows with an average body weight of 72.8±3.6 kg were allotted to one of six dietary treatments in a randomized complete block design conducted for 35 d. Each diet was fed to five pens of pigs containing four barrows. A normal crude protein (CP) diet providing 15.3% CP and 0.71% SID Lys and five low CP diets providing 12% CP with SID Lys concentrations of 0.51, 0.61, 0.71, 0.81 and 0.91% were formulated. Increasing the SID Lys content of the diet resulted in an increase in weight gain (linear effect p = 0.04 and quadratic effect p = 0.08) and an improvement in feed conversion ratio (FCR) (linear effect p = 0.02 and quadratic effect p = 0.02). For weight gain and FCR, the estimated SID Lys requirement of finishing barrows were 0.71 and 0.71% (linear broken-line analysis), 0.79 and 0.78% (quadratic analysis), respectively. Exp. 2 was a 26 d dose-response study using SID Thr to Lys ratios of 0.56, 0.61, 0.67, 0.72 and 0.77. A total of 138 barrows weighing 72.5±4.4 kg were randomly allotted to receive one of the five diets. All diets were formulated to contain 0.61% SID Lys (10.5% CP), which is slightly lower than the pig’s requirement. Weight gain was quadratically (p = 0.03) affected by SID Thr to Lys ratio while FCR was linearly improved (p = 0.02). The SID Thr to Lys ratios for maximal weight gain and minimal FCR and serum urea nitrogen (SUN) were 0.67, 0.71 and 0.64 using a linear broken-line model and 0.68, 0.78 and 0.70 using a quadratic model, respectively. Based on the estimates obtained from the broken-line and quadratic analysis, we concluded that the dietary SID Lys requirement for both maximum weight gain and minimum FCR was 0.75%, and an optimum SID Thr to Lys ratio was 0.68 to maximize weight gain, 0.75 to optimize FCR and 0.67 to minimize SUN for finishing barrows.

Effects of folic acid on the performance of suckling piglets and sows during lactation

BACKGROUND

The present research was conducted to investigate the influences of supplementation with different levels of folic acids in diet on the performance of lactating sows. Twenty Landrace × Yorkshire sows received the same basal corn-soybean diets (folic acid, 1.3 mg kg(-1)) from gestation to parturition (day 107). After parturition, sows were allotted to four treatments: control group (folic acid supplementation level, 0 mg kg(-1)), group 1 (12.5 mg kg(-1)), group 2 (50 mg kg(-1)) and group 3 (100 mg kg(-1)), with five replicates of one sow. The experiment lasted for 21 days.

RESULTS

(1) Folic acid increased milk production (P > 0.05). (2) Compared with the control, supplementation with folic acid (100 mg kg(-1)) increased the concentration of butter fat, total substance and non-lipoid substance significantly (P < 0.01), the concentration of milk protein was also significantly increased in group 2 and group 3 (P < 0.01) in milk. (3) Folic acid supplementation could increase litter weaning weight, average piglet weaning weight and average piglet daily gain (P > 0.05).

CONCLUSION

These results suggested that supplementation with folic acid in the diets of lactating sows increases milk production, improved milk quality and the performance of piglets.