Limits to starch digestion in the ruminant small intestine

Evaluation of hindgut buffers under high-starch diet conditions in lactating Holstein cows

Buffering of the rumen environment can alleviate some of the negative effects of acidosis, and the same may hold true in the hindgut. The objective of this study was to evaluate the potential for 2 dietary buffers at different dosages to mitigate excessive intestinal fermentation and systemic inflammation due to hindgut acidosis. Ten ruminally cannulated lactating cows were randomly assigned to a replicated 5 × 5 Latin square with a 7-d adaptation period, 14-d experimental periods, and 7-d washout periods between each experimental period. Daily treatments during experimental periods were abomasal infusion of water without feeding supplemental buffer (CON), abomasal infusion of corn starch without feeding supplemental buffer (IS), or abomasal infusion of starch with 150 g/d of buffer A (calcium carbonate, magnesium oxide, and crushed oyster shell blend; T1), 300 g/d of buffer A (T2), or 150 g/d of buffer B (magnesium oxide; T3). Daily abomasal starch infusions were 2 g/kg BW in period 1 and 4 g/kg BW in periods 2-5 and split into 2 bolus infusions, provided every 12 h during the 14-d experimental periods. Cows were fed a 30.9% starch TMR (on a DM basis) and 1 cow was removed from the study between periods 1 and 2. Although not intended, the high starch TMR seemed to induce SARA, as evidenced by mean rumen pH of 5.8 to 6.0. Compared with CON, abomasal corn starch addition decreased fecal pH (6.80 vs. 6.37) and apparent total-tract starch digestibility (95.6 vs. 86.1%). Starch infusion did not increase serum acute phase proteins, and effects on fecal LPS and total fecal VFA concentrations were modest, suggesting that infused starch was only partially digested. Buffer addition increased fecal pH as expected (mean of 6.76 for T1, T2 and T3, respectively), but also increased fecal acetate (64.0 mM for IS compared with a mean of 74.5 mM for T1, T2 and T3, respectively) and total VFA concentration (81.5 mM for IS compared with a mean of 100.1 mM for T1, T2, and T3, respectively), suggesting that they may have increased hindgut fermentation. Additionally, the T2 treatment may have had an inflammatory effect as evidenced by increased serum amyloid A compared with IS (71.5 vs. 22.0 µM, respectively). Despite increased fecal pH, the inclusion of different buffer formulations in a high starch diet seemed to increase hindgut fermentation as evidenced by increased VFA concentration. The buffers employed in this experiment did not alleviate the negative effects of abomasal starch infusions and, in the case of T2, may have presented a challenge.

Effects of replacing barley grain with corn grain on performance, rumen and blood parameters in dairy cows fed alfalfa hay or corn silage

Different grain sources in the diet have shown varying effects on performance of dairy cows. Also, the variability in response to different starch sources is influenced by the type of forage used. This study investigates the combined effects of two forage (alfalfa hay vs. corn silage) and grain (barley vs. corn) sources on dry matter intake (DMI), feed efficiency, milk production and composition, apparent nutrient digestibility, blood metabolites, and ruminal metabolism of dairy cows. Eight second-parity early lactation Holstein cows (63 ± 5 d in milk) were used in a replicated 4 × 4 Latin square with a 2 × 2 factorial design. Diets were iso-energetic and iso-nitrogenous and were based on either corn (CG) or barley (BG) grains, and corn silage (CS) or alfalfa hay (AH). Diets with CS had more long (108 vs. 68 g/kg DM) and medium particles (369 vs. 331 g/kg DM), and thus, longer mean particle size (5.4 vs. 4.6 mm) compared to diets with AH. Cows fed BG had less DMI and lower actual and energy-corrected milk (ECM) yield than CG-fed cows. The total tract digestibility of starch (952 vs. 987 g/kg) and crude protein (CP) (687 vs. 743 g/kg) were lower in CG cows than cows fed BG. Additionally, cows fed CG tended to have lower ruminal propionate concentrations than those fed BG, suggesting differences in ruminal fermentability between BG and CG. Milk fat content (30.6 vs. 29.2 g/kg) and ECM production (42.6 vs. 40.7 kg/d) tended to be greater in cows fed diets containing AH rather than CS. Furthermore, despite similar nutrient digestibility and total volatile fatty acid production, AH-fed cows had a higher ruminal acetate-to-propionate ratio compared to those fed CS. Replacement of BG with CG improved performance by increasing DMI; however, the expected positive effects of substituting CS with AH in BG-based diets may be obscured by the impact of differences in forage particle size (PS). These results indicated that inclusion of CG might be an optimum choice for modulating ruminal condition and enhancing performance compared to BG during early lactation.

Malted Barley as a Potential Feed Supplementation for the Reduction of Enteric Methane Emissions, Rumen Digestibility, and Microbiome Community Changes in Laboratory Conditions

Three sets of in vitro rumen fermentation experiments were conducted to determine the effects of diets that included malted barley (MB) and basal diets (grain- and forage-based) on the in vitro gas production, greenhouse gas (GHG) emissions, rumen fermentation profiles, and microbiome changes in the rumen when supplemented with feedlot or dairy rations. The first experiment (Exp. 1) was conducted to evaluate the effects of various levels of MB (0% [referred to as a control], 10%, 20%, and 30%, as-fed basis) supplemented with a grain-based diet in a feedlot ration (2.5 g/bottle) after 48 h ruminal incubation on the in vitro gas production, GHG emissions, and rumen fermentation rate. The second two sets of in vitro experiments (Exp. 2a, b) were conducted to determine (1) the effects of linear dose levels of malted barley (MB; 0%, 10%, 20%, 30%, and 40% as-fed) with two different basal diets (grain-based and forage-based) and (2) the effects of different sources of MB (control, Korean, Canadian, and the USA; 30% MB, as-fed) in a dairy ration after 24 h incubation on in vitro gas production, rumen fermentation profiles, GHG emissions (methane [CH4] and nitrous oxide [N2O]), in vitro dry matter disappearance rate (IVDMD), and microbiome changes. Commercially available α-amylase (0.2 g/100 mL) was used as a sub-control in Exp. 2a. Using gas chromatography, all gases were collected using an ANKOM Gas Production system and analyzed for CH4 and N2O. In Exp. 1, total gas production, cumulative gas, and GHG productions (CH4, N2O) linearly decreased (p ≤ 0.05) with increasing MB supplementation. In Exp. 2a, cumulative in vitro gas, total gas production, and rumen fermentation profiles (e.g., total VFA, acetate, butyrate, iso-butyrate, valerate, and iso-valerate) linearly decreased (p < 0.05-0.01) with increasing MB supplementation, with diet-treatment interactions (p < 0.001). In addition, CH4 and N2O production (mL/g DM) linearly and quadratically decreased (p < 0.01) with increasing MB supplementation across the diets. However, IVDMD linearly and/or quadratically increased (p < 0.01) with increasing MB, with diet-treatment interactions (p < 0.001). The average populations of Bacteroidetes, Proteobacteria, and Spirochaetes were significantly decreased (p < 0.01-0.001) for MB treatment groups compared to the control group. Therefore, it may be possible to suppress methane production directly and indirectly by adding MB and α-amylase by modifying ruminal fermentation profiles.

Net energy of grains for dairy goats differed with processing methods and grain types

BACKGROUND

The diverse types and processing methods of grains intricately influence the sites and digestibility of starch digestion, thereby impacting energy utilization. This study aimed to explore the impact of grain variety and processing methods on the net energy (NE) in dairy goats, analyzing these effects at the level of nutrient digestion and metabolism.

METHODS

Eighteen castrated Guanzhong dairy goats (44.25 ± 3.59 kg BW) were randomly divided into 3 groups, each consisting of 6 replicates. The substitution method was employed to determine the NE values of the dry-rolled corn (DRC), dry-rolled wheat (DRW) or steam-flaked corn (SFC, 360 g/L). Briefly, two phases were performed. Throughout the basal phase, all goats were fed the same basal diet. In the substitution phase, 30% of the basal diet was replaced with DRC, DRW and SFC, respectively.

RESULTS

In this study, the NE values of the DRC, DRW and SFC were 7.65, 7.54 and 7.44 MJ/kg DM, respectively. Compared to the DRC group, the DRW group showed increased digestibility of starch and crude protein (CP). Similarly, the SFC group exhibited increased organic matter (OM) and starch digestibility and a trend towards higher dry matter (DM) digestibility, reduced fecal OM and starch content. Additionally, fecal volatile fatty acid (VFA) concentrations decreased in goats fed SFC. Correspondingly, digestible energy (DE) in the DRW and SFC groups tended to be higher than in the DRC group. DRW increased total VFA concentration compared to DRC, while SFC increased the proportion of propionate and decreased the acetate-to-propionate ratio in the rumen. Both the DRW and SFC diets elevated serum glucose levels. Furthermore, heat increment (HI) and gaseous energy (GasE) related to fermentation were significantly higher in the DRW and SFC groups compared to the DRC group.

CONCLUSION

Our findings indicated that DRW and SFC increased rumen starch fermentation in goats, thereby improving total tract starch digestion and DE. However, DRW and SFC failed to improve NE value due to increased heat and gas energy production from fermentation. Therefore, excessively refined grains processing in the diet of dairy goats does not effectively improve energy efficiency.

Supplemental effects of rumen-protected L-tryptophan at various levels on starch digestion, melatonin and gastrointestinal hormones in Holstein steers

The effects of different level of rumen-protected L-tryptophan (RPL-T) supplementation on starch digestion, melatonin (MEL) and gastrointestinal (GI) hormones secretion in Holstein steers were evaluated. Four Holstein steers (201 ± 24 kg) were employed in a 4×4 Latin square design. The dietary treatments were the control (basal diet) and RPL-T groups of basal diet + 191.1 mg/kg body weight (BW), basal diet + 95.6 mg/kg BW, and basal diet + 19.1 mg/kg BW groups. Blood samples were collected to measure blood hormones on day 0, 1, 3, and 5 of the experiment to study serum MEL and GI tract and duodenal starch degradability. The design was 4 × 4 Latin square and the data were analyzed using the ANOVA procedure by SPSS. The D-glucose content in the RPL-T treatment groups was significantly reduced (p < 0.05) compared to the control group. The serum cholecystokinin (CCK) levels were increased in the RPL-T treatment group compared to the control group. However, there was no significant difference between all RPL-T treatment groups. The results of serum MEL were also similar to CCK results. The serum secretin levels were not significantly different (p > 0.05) between all groups. The apparent starch disappearance rates in GI track were lower (p < 0.05) in treatment groups compared with the control, and there was no significant difference between all RPL-T treatment groups. Digestion was increased (p < 0.05) in all treatment groups compared to the control. Overall, there were significant differences in starch digestibility, CCK, and MEL compared to the control group, but there were no significant differences in concentration of RPL-T. Therefore, considering the economic purpose, 19.1mg/kg BW is recommended as an appropriate level of addition to increase the productivity of beef cattle.

Low expression of CCKBR in the acinar cells is associated with insufficient starch hydrolysis in ruminants

Unlike monogastric animals, ruminants exhibit significantly lower starch digestibility in the small intestine. A better understanding of the physiological mechanisms that regulate digestion patterns in ruminants could lead to an increased use of starch concentrates. Here we show more robust pancreatic exocrine function in adult goats (AG) than in neonatal goats (NG) by combining scRNA-seq and proteomic analysis. Our findings suggest that inadequate amylase activity could be a limiting factor in starch digestion in ruminants. In addition, we show that insufficient starch hydrolysis in adult goats might be associated with low expression of a CCKBR receptor in the acinar cells. On top of that, the low expression of CCKBR in adult goats, in conjunction with a low distribution of the CCK-I cells in the duodenum, may jointly lead to a slow response of the intestinal-pancreatic reflex and induce an asynchronous process of food entering the small intestine and releasing of digestive enzymes, which ultimately limits the starch digestibility. Overall, the present findings generate a resource that can provide better insight into the mammalian pancreas.

Influence of postruminal casein infusion and exogenous glucagon-like peptide 2 administration on the jejunal mucosal transcriptome in cattle

We previously demonstrated that postruminal casein infusion and exogenous glucagon-like peptide 2 (GLP-2) administration independently stimulated growth and carbohydrase activity of the pancreas and jejunal mucosa in cattle. The objective of the current study was to profile the jejunal mucosal transcriptome of cattle using next-generation RNA sequencing in response to postruminal casein infusion and exogenous GLP-2. Twenty-four Holstein steers [250 ± 23.1 kg body weight (BW)] received a continuous abomasal infusion of 3.94 g raw corn starch/kg of BW combined with either 0 or 1.30 g casein/kg of BW for 7 d. Steers received subcutaneous injections at 0800 and 2000 h to provide either 0 or 100 μg GLP-2/kg of BW per day. At the end of the 7-d treatment period, steers were slaughtered for collection of the jejunal mucosa. Total RNA was extracted from jejunal mucosal tissue, strand-specific cDNA libraries were prepared, and RNA sequencing was conducted to generate 150-bp paired-end reads at a depth of 40 M reads per sample. Differentially expressed genes (DEG), KEGG pathway enrichment, and gene ontology enrichment were determined based on the FDR-corrected P-value (padj). Exogenous GLP-2 administration upregulated (padj < 0.05) 667 genes and downregulated 1,101 genes of the jejunal mucosa. Sphingolipid metabolism, bile secretion, adherens junction, and galactose metabolism were among the top KEGG pathways enriched with upregulated DEG (padj < 0.05) in response to exogenous GLP-2 administration. The top gene ontologies enriched with upregulated DEG (padj < 0.05) in response to exogenous GLP-2 administration included nutrient metabolic processes, brush border and bicellular tight junction assembly, and enzyme and transporter activities. Exogenous GLP-2 administration increased or tended to increase (padj < 0.10) brush border carbohydrase (MGAM, LCT, TREH), hexose transporter (SLC5A1, SLC2A2), and associated transcription factor (HNF1, GATA4, KAT2B) mRNA expression of the jejunal mucosa. Gene ontologies and KEGG pathways that were downregulated (padj < 0.05) in response to exogenous GLP-2 were related to genetic information processing. Postruminal casein infusion downregulated (padj < 0.05) 7 jejunal mucosal genes that collectively did not result in enriched KEGG pathways or gene ontologies. This study highlights some of the transcriptional mechanisms associated with increased growth, starch assimilation capacity, and barrier function of the jejunal mucosa in response to exogenous GLP-2 administration.

Lactational performance, ruminal fermentation, and enteric gas emission of dairy cows fed an amylase-enabled corn silage in diets with different starch concentrations

This study investigated the effects of feeding an amylase-enabled corn silage (ACS) on the performance and enteric gas emissions in lactating dairy cows. Following a 2-wk covariate period, 48 mid-lactation Holstein cows were assigned to 1 of 3 treatments in a 10-wk randomized complete block design experiment. Treatments were diets containing the same proportion of corn silage (40% of dietary DM) as follows: (1) a conventional hybrid corn silage control (CON), (2) ACS replacing the control silage (ADR), and (3) the ADR diet replacing soybean hulls with ground corn grain to achieve the same dietary starch concentration as CON (ASR). Control corn silage and ACS were harvested on the same day and contained 40.3% and 37.1% DM and (% of DM): 37.2% and 41.0% NDF and 37.1% and 30.0% starch, respectively. Enteric gas emissions were measured using the GreenFeed system. Two cows were culled due to health-related issues during the covariate period. Ruminal fluid was collected from 24 cows (8 per treatment) using the orogastric ruminal sampling technique. When compared with CON, cows fed ADR had increased DMI during experimental wk 3, 4, and 9, but treatment did not affect milk or ECM milk yields (39.0 kg/d on average; SEM = 0.89). Compared with CON, feed efficiency (per unit of milk, but not ECM) tended to be lower for ADR, whereas milk true protein concentration (a tendency) and yield were lower for ASR. Milk urea N was decreased by both ADR and ASR diets relative to CON. Compared with CON, daily CH4 emission and emission intensity were increased by ADR but not ASR. Total protozoal count tended to be increased by both diets formulated with ACS when compared with control corn silage. Total-tract digestibility of dietary NDF was greater for ASR, and that of ADF was greater for both ADR and ASR versus CON. The molar proportion of acetate (a tendency) and acetate-to-propionate ratio were increased by ADR, but not ASR, when compared with CON. Replacement of CON with ACS (having lower starch concentration) in the diet of dairy cows increased DMI during the initial weeks of the experiment, maintained ECM, tended to decrease feed efficiency, and increased enteric CH4 emissions, likely due to increased intake of digestible fiber, compared with CON.

Impact of combined management strategies of monensin and virginiamycin in high energy diets on ruminal fermentation and nutrients utilization

Feed additives such as monensin (MON) and virginiamycin (VM) are commonly utilized in feedlot diets to enhance rumen fermentation. Nevertheless, the precise effects of combining MON and VM during specific feedlot periods and the advantages of this combination remain unclear. This study was designed to investigate the effects of withdrawal of MON when associated with VM during the adaptation and finishing periods on ruminal metabolism, feeding behavior, and nutrient digestibility in Nellore cattle. The experimental design was a 5 × 5 Latin square, where each period lasted 28 days. Five rumen-cannulated Nellore yearling bulls were used (414,86 ± 21,71 kg of body weight), which were assigned to five treatments: (1) MON during the entire feeding period; (2) VM during the entire feeding period; (3) MON + VM during the adaptation period and only VM during the finishing period 1 and 2; (4) MON + VM during the entire feeding period; (5) MON + VM during the adaptation and finishing period 1 and only VM during the finishing period 2. For the finishing period 1, animals fed T3 had improved potential degradability of dry matter (p = 0.02). Cattle fed T3 and T5 had the highest crude protein degradability when compared to animals receiving T2 (p = 0.01). Animals fed T2 and T3 had reduced the time (p < 0.01) and area under pH 6.2 (p = 0.02). Moreover, animals fed T4 had greater population of protozoa from the genus Diplodinium (p = 0.04) when compared to those from animals fed T2, T3 and T5. For the finishing period 2, animals fed T3 had greater starch degradability when compared to animals receiving T4 and T5 (p = 0.04). Animals fed T3, T4 and T5 had increased the duration of time in which pH was below 5.6 (p = 0.03). The area under the curve for ruminal pH 5.2 and pH 5.6 was higher for the animals fed T3 (p = 0.01), and the area under pH 6.2 was higher for the animals fed T3 and T5 (p < 0.01) when compared to animals receiving T2. There is no substantial improvement on the rumen fermentation parameters by the concurrent utilization of MON and VM molecules, where the higher starch and protein degradability did not improve the rumen fermentation.

Effects of the kinetic pattern of dietary glucose release on nitrogen utilization, the portal amino acid profile, and nutrient transporter expression in intestinal enterocytes in piglets

BACKGROUND

Promoting the synchronization of glucose and amino acid release in the digestive tract of pigs could effectively improve dietary nitrogen utilization. The rational allocation of dietary starch sources and the exploration of appropriate dietary glucose release kinetics may promote the dynamic balance of dietary glucose and amino acid supplies. However, research on the effects of diets with different glucose release kinetic profiles on amino acid absorption and portal amino acid appearance in piglets is limited. This study aimed to investigate the effects of the kinetic pattern of dietary glucose release on nitrogen utilization, the portal amino acid profile, and nutrient transporter expression in intestinal enterocytes in piglets.

METHODS

Sixty-four barrows (15.00 ± 1.12 kg) were randomly allotted to 4 groups and fed diets formulated with starch from corn, corn/barley, corn/sorghum, or corn/cassava combinations (diets were coded A, B, C, or D respectively). Protein retention, the concentrations of portal amino acid and glucose, and the relative expression of amino acid and glucose transporter mRNAs were investigated. In vitro digestion was used to compare the dietary glucose release profiles.

RESULTS

Four piglet diets with different glucose release kinetics were constructed by adjusting starch sources. The in vivo appearance dynamics of portal glucose were consistent with those of in vitro dietary glucose release kinetics. Total nitrogen excretion was reduced in the piglets in group B, while apparent nitrogen digestibility and nitrogen retention increased (P < 0.05). Regardless of the time (2 h or 4 h after morning feeding), the portal total free amino acids content and contents of some individual amino acids (Thr, Glu, Gly, Ala, and Ile) of the piglets in group B were significantly higher than those in groups A, C, and D (P < 0.05). Cluster analysis showed that different glucose release kinetic patterns resulted in different portal amino acid patterns in piglets, which decreased gradually with the extension of feeding time. The portal His/Phe, Pro/Glu, Leu/Val, Lys/Met, Tyr/Ile and Ala/Gly appeared higher similarity among the diet treatments. In the anterior jejunum, the glucose transporter SGLT1 was significantly positively correlated with the amino acid transporters B0AT1, EAAC1, and CAT1.

CONCLUSIONS

Rational allocation of starch resources could regulate dietary glucose release kinetics. In the present study, group B (corn/barley) diet exhibited a better glucose release kinetic pattern than the other groups, which could affect the portal amino acid contents and patterns by regulating the expression of amino acid transporters in the small intestine, thereby promoting nitrogen deposition in the body, and improving the utilization efficiency of dietary nitrogen.

The influence of virginiamycin on digestion and ruminal parameters under feedlot conditions

This experiment aimed to assess the impact of virginiamycin on in vitro gas production dynamics, rumen kinetics, and nutrient digestibility in beef steers fed a grain-based diet. Nine ruminally cannulated British-crossbred steers (596 ± 49 kg) were assigned to this experiment. Animals were housed in three pens (n = 3/pen) equipped with a Calan gate feed system and water troughs. Pens were enrolled in a 3 × 3 Latin square design containing three periods of 16 d, and a 5-d washout interval between periods. Dietary treatments consisted of virginiamycin (VM) administration at 0 (VM0), 180 (VM180), or 240 mg/d (VM240). During days 15 and 16 of each period, about 600 mL of rumen fluid and urine samples were collected before (0 h), and at 4, 8, 12, and 16 h after the morning feed (0730 hours), rumen inoculum was used to take pH and redox potential measurements immediately after collection using a portable pH and redox meter, and subsamples were taken for volatile fatty acids (VFA) and NH3-N analyses, and urine samples were composited daily and analyzed for creatinine and purine derivatives (PD) content to estimate microbial crude protein flow. During the 4-h post-morning feed rumen collection, rumen inoculum was utilized to perform in vitro gas production measurements. Fecal samples were collected on day 16 of each period to estimate nutrient digestibility using acid detergent insoluble ash as an internal marker. Animals were considered the experimental unit for the statistical analyses, and periods and squares were included as random variables. The total and rate of gas production were similar among treatments (P ≥ 0.17). The second-pool (i.e., fiber) gas production increased linearly as VM inclusion increased (P = 0.01), with VM240 being greater compared to VM180 and VM0 (7.84, 6.94, and 6.89 mL, respectively). Ruminal pH linearly increased as VM increased, with VM240 being greater than VM0 and VM180 intermediate (5.90, 5.82, and 5.86, respectively; P = 0.03). The VFA concentrations did not differ (P ≥ 0.13), but the acetate-to-propionate ratio was the highest in VM240 (P = 0.005). Branched-chain VFA increased (P ≤ 0.03) while lactate concentrations decreased (P = 0.005) linearly with VM. The ruminal NH3-N concentration was the lowest in the VM0 (P = 0.006). The estimated absorbed PD, purine derivative to creatinine index, and microbial N flow increased linearly with VM (P ≤ 0.07). The provision of VM influenced rumen dynamics in a dose-dependent manner.

Whole-body urea kinetics and functional roles of urea transporters and aquaporins in urea secretion into the rumen in sheep fed diets varying in crude protein content and corn grain processing method

The objectives were to determine the effects of dietary crude protein (CP) content and corn grain processing on whole-body urea kinetics and the functional roles of urea transporter-B (UT-B) and aquaporins (AQP) in serosal-to-mucosal urea flux (Jsm-urea) in ovine ruminal epithelia. Thirty-two Rideau-Arcott ram lambs were blocked by bodyweight into groups of 4 and then randomly allocated within blocks to 1 of 4 diets (n = 8) in a 2 × 2 factorial design. Dietary factors were CP content (11% [LP] vs. 16% [HP]) and corn grain processing (whole-shelled [WSC] vs. steam-flaked [SFC] corn). Whole-body urea kinetics and N balance were determined using 4-d continuous intrajugular infusions of [15N15N]-urea with concurrent collections of urine and feces with four blocks of lambs (n = 4). After 23 d on diets, lambs were killed to collect ruminal epithelia for mounting in Ussing chambers to determine Jsm-urea and the measurement of mRNA abundance of UT-B and AQP. Serosal and mucosal additions of phloretin and NiCl2 were used to inhibit UT-B- and AQP-mediated urea transport, respectively. Lambs fed HP had a greater (P < 0.01) N intake (29.4 vs. 19.1 g/d) than those fed LP; however, retained N (g/d or % of N intake) was not different. As a % of N intake, lambs fed SFC tended (P = 0.09) to have a lower N excretion (72.2 vs. 83.5%) and a greater N retention (27.8 vs. 16.6%) compared to those fed WSC. Endogenous urea-N production (UER) was greater in lambs fed HP compared to those fed LP (29.9 vs. 20.6 g/d; P = 0.02), whereas urea-N secreted into the gut (GER; g/d) and urea-N used for anabolic purposes (UUA; g/d) were similar. Lambs fed LP tended (P = 0.05) to have greater GER:UER (0.78 vs. 0.66) and UUA:GER (0.23 vs. 0.13) ratios, and a greater Jsm-urea (144.7 vs. 116.1 nmol/[cm2 × h]; P = 0.07) compared to those fed HP. Lambs fed SFC tended to have a lower NiCl2-insensitive Jsm-urea (117.4 vs. 178.4 nmol/[cm2 × h]; P = 0.09) and had a lower phloretin-insensitive Jsm-urea (87.1 vs. 143.1 nmol/[cm2 × h]; P = 0.02) compared to those fed WSC. The mRNA abundance of UT-B (0.89 vs. 1.07; P = 0.08) and AQP-3 (0.90 vs. 1.05; P = 0.07) tended to be lower in lambs fed SFC compared to those fed WSC. Overall, reducing CP content tended to increase the GER:UER ratio with no changes in the expression or function of UT-B and AQP. Although corn grain processing had no effects on GER, feeding SFC increased the portion of urea secretion into the rumen that was mediated via UT-B and AQP.

Laminaria japonica Polysaccharides Improves the Growth Performance and Faecal Digestive Enzyme Activity of Weaned Piglets

The aim of this experiment was to investigate the effect of Laminaria japonica polysaccharide (LJP) supplementation at levels of 100, 200, or 400 mg/kg on the growth performance, faecal digestive enzyme activity, and serum biochemistry and amino acids of weaned piglets. One hundred and twenty weaned piglets (Barkshire × Licha Black, 21 days old, 6.13 ± 0.16 kg) were randomly divided into four groups with five replicates of six piglets in each group based on body weight. Piglets were fed with different levels (0, 100, 200, and 400 mg/kg) of LJP for a 21-day trial. On day 21, faecal and blood samples were collected from one piglet per pen. The results showed that the supplementation of the 200 and 400 mg/kg LJP significantly increased average daily gain (ADG) and average daily feed intake (ADFI) compared to the control group (p = 0.007; p = 0.002), and dietary LJP linearly increased ADG and ADFI (p = 0.002; p < 0.001). In addition, the supplementation of the 200 and 400 mg/kg LJP significantly increased faecal amylase activity (p < 0.001) compared to the control group, and dietary LJP linearly increased faecal amylase and lipase activities (p = 0.001; p = 0.037). Moreover, dietary LJP at 400 mg/kg increased serum histidine content compared to the other groups (p = 0.002), and dietary LJP linearly increased the contents of serum histidine and asparagine in piglets (p < 0.001; p = 0.046). In conclusion, supplementation of 200 and 400 mg/kg LJP could enhance growth performance and faecal digestive enzyme activity and modulate the serum amino acid content of weaned piglets, potentially contributing to the health of weaned piglets.

Effect of short-term abomasal corn starch infusions on postruminal fermentation and blood measures

It is possible that some of the systemic responses to subacute ruminal acidosis (SARA) may be caused by increased intestinal starch fermentation. The objective of this experiment was to evaluate the effect of abomasal infusion of up to 3 g of corn starch/kg body weight (approximately 1.6 kg of starch/d) on fecal measures of fermentation, plasma acute phase proteins, and white blood cell populations. Six ruminally cannulated cows in late lactation were randomly assigned to duplicate 3 × 3 Latin squares with 21-d periods. Cows were fed a 20.6% starch TMR twice daily and during the last 7 d of each period cows were abomasally infused with corn starch at 0 (CON), 1 (ST1), or 3 (ST3) g/kg body weight split into 2 bolus infusions, provided every 12 h. Fecal samples were collected at 0, 6, 12, and 18 h following feeding on d 21 and were analyzed for pH, VFA, lactic acid, and lipopolysaccharide (LPS). Composite fecal samples were used to estimate apparent total-tract nutrient digestibility using undigested neutral detergent fiber as an internal marker. Blood samples were collected at 0 and 6 h relative to feeding on d 14, 18, and 21 of each period. Concentrations of haptoglobin and serum amyloid A in plasma were measured in all samples, 0 h samples on d 14 and 21 were used to measure white blood cell populations, and 0 h samples from d 14, 18, and 21 were used for flow cytometric analysis of γδ T cells. Data were analyzed in SAS using models that included fixed effects of treatment and period and the random effects of cow and square. For blood measures, d 14 samples collected before the initiation of abomasal infusions were included as covariates. Time (d or h) was added as a repeated measure in variables that included multiple samples during the abomasal infusion period. A contrast was used to determine the linear effect of increasing abomasal corn starch. Abomasal corn starch linearly decreased fecal pH and linearly increased fecal total VFA and LPS, but effects were modest, with fecal pH, total VFA, and LPS changing from 6.96, 57.7 mM, and 4.14 log10 endotoxin units (EU) per gram for the CON treatment to 6.69, 64.1 mM, and 4.58 log10 EU/g for the ST3 treatment, respectively. This suggests that we did not induce hindgut acidosis. There were no effects of treatment on apparent total-tract starch digestibility or fecal starch content (mean of 96.9% and 2.2%, respectively). Treatment did not affect serum acute phase proteins or most circulating white blood cells, but the proportion of circulating γδ T cells tended to linearly decrease from 6.69% for CON to 4.61% for ST3. Contrary to our hypothesis, increased hindgut starch fermentation did not induce an inflammatory response in this study.

Short communication: Impact of corn grain particle size on production performance of lactating dairy cows

Corn grain particle size has the potential to influence the performance of lactating dairy cows and the overall profitability of a dairy farm. The objective of this study was to evaluate the productive performance of lactating cows fed diets containing finely or coarsely ground corn grain. Fifty lactating Holstein cows (n = 50; 10 primiparous and 40 multiparous), averaging (mean ± standard deviation, SD) 658 ± 64 kg of BW, 38.8 ± 7.3 kg of milk/d, and 155 ± 80 DIM, were fed diets with finely ground corn grain (FGC) or coarsely ground corn grain (CGC) in a randomized block design with a 28-d treatment period. Finely and coarsely ground corn grain had an average particle size of 660 and 915 µm, respectively. Dry matter intake (DMI) was reduced (p < 0.01) for cows fed FGC (22.1 vs. 21.2 kg d-1). Milk yield and efficiency were not affected by treatments (37.9 vs. 36.8 kg d-1; p = 0.12 and 1.78 vs. 1.79; p = 0.15). Concentrations of milk protein and fat, as well as other milk solids, were unaffected (p > 0.05) by treatments. Fecal starch (FS) concentrations were greater (p < 0.01) for cows fed CGC (7.0 vs. 4.9%), whereas plasma concentrations of D-lactate were greater (p < 0.05) for cows fed FGC (98.5 vs. 79.7 µM). Overall, feeding finely ground corn grain increased total-tract starch digestibility and reduced DMI while maintaining milk yield.

Reduction of Escherichia coli O157:H7 in Finishing Cattle Fed Corn Genetically Modified to Produce Increased Concentrations of Alpha Amylase in the Corn Kernel

Cattle are recognized as the principal reservoir for Escherichia coli O157:H7 and preharvest food safety efforts often focus on decreasing shedding of this pathogen in cattle feces. Enogen® corn (EC; Syngenta Seeds, LLC) is genetically modified to produce enhanced concentrations of α-amylase in the corn kernel endosperm. Research has demonstrated improvements in feed efficiency for cattle fed EC and research has not yet explored whether improved digestion impacts foodborne pathogen populations in cattle. Therefore, this study explored effects of finishing diets containing EC on Escherichia coli O157:H7 prevalence in cattle. A 2 × 2 factorial experiment was conducted with steers (n = 960) fed diets consisting of 2 types of silage (EC or Control) and grain (EC or Control), fed daily ad libitum. Steers were grouped into 12 blocks by incoming body weight, blocks were randomly assigned to one of four pens, and pens were randomly assigned to one diet. Cattle were sampled using rectoanal mucosal swabs in cohorts of 298-337 cattle per day, for a total of 3 sampling days (15-16 days apart). Escherichia coli O157:H7 prevalence rates ranged from not detected (0/75) to 10.0% (8/80) depending on sampling day. Tests for the silage × corn interaction, and the main effects of silage and corn, were not significant (p > 0.05); however, EC reduced the odds of Escherichia coli O157:H7 prevalence by 43% compared to the control corn diet (p = 0.07). Diets containing EC tended to decrease Escherichia coli O157:H7 prevalence in feedlot cattle; however, this reduction was not significant. Before a conclusion can be drawn about impact of EC on Escherichia coli O157:H7 in cattle, further research is necessary to (1) determine if this tendency is due to increased alpha amylase activity and (2) elucidate impact on Escherichia coli O157:H7 prevalence and concentration, as well as a possible mechanism of action.

Postruminal Casein Infusion and Exogenous Glucagon-Like Peptide 2 Administration Differentially Stimulate Pancreatic α-Amylase and Small Intestinal α-Glucosidase Activity in Cattle

BACKGROUND

Increasing luminal carbohydrate flow decreases pancreatic α-amylase activity but can increase jejunal maltase activity, suggesting that regulation of carbohydrase activity is perhaps uncoordinated in response to luminal carbohydrate flow. Increasing luminal casein flow increases pancreatic α-amylase activity in cattle, and exogenous glucagon-like peptide 2 (GLP-2) has been shown to increase small intestinal α-glucosidase activity in nonruminants.

OBJECTIVES

The objective was to evaluate the effects of postruminal casein infusion, exogenous GLP-2, or their combination on endogenous pancreatic and small intestinal carbohydrase activity in cattle postruminally infused with starch.

METHODS

Holstein steers [n = 24; 250 ± 23 kg body weight (BW)] received a continuous abomasal infusion of 3.94 g raw corn starch/kg of BW combined with either 0 or 1.30 g casein/kg of BW. Steers received subcutaneous injections in 2 equal portions daily of excipient (0.5% bovine serum albumin) or 100 μg GLP-2/kg of BW per day. At the end of the 7-d treatment period, steers were slaughtered for tissue collection. Data were analyzed using the MIXED procedure of SAS version 9.4 (SAS Institute Inc.).

RESULTS

Postruminal casein infusion increased (P ≤ 0.03) pancreatic mass by 12.6%, total pancreatic α-amylase activity by 50%, and postruminal starch disappearance from 96.7% to 99.3%. Exogenous GLP-2 increased (P < 0.01) total small intestinal and mucosal mass by 1.2 kg and 896 g, respectively. Relative to control, GLP-2 and casein + GLP-2 increased (P = 0.04) total small intestinal α-glucosidase activity by 83.5%. Total small intestinal maltase, isomaltase, and glucoamylase activity was 90%, 100%, and 66.7% greater for GLP-2 and casein + GLP-2 steers compared with control.

CONCLUSIONS

Casein increased pancreatic α-amylase activity, GLP-2 increased small intestinal α-glucosidase activity, and the combination of casein and GLP-2 increased both pancreatic α-amylase activity and small intestinal α-glucosidase activity. This novel approach provides an in vivo model to evaluate effects of increasing endogenous carbohydrase activity on small intestinal starch digestion.

Mitogen-activated protein kinase-interacting kinase 1 is involved in mTOR-mediated pancreatic exocrine function of bovine pancreatic acinar cells with leucine supply

Leucine improves the exocrine capacity of the cow pancreas, but the mechanism was not revealed clearly. Mitogen-activated protein kinase-interacting kinase 1 (MNK1) is a pancreatic acinar cell-specific stress response kinase that regulates digestive enzyme abundance. We aimed to investigate the MNK1 gene and protein expression profiles among various organs or tissues of dairy cows and to demonstrate the mechanism by which leucine-stimulated MNK1 regulates pancreatic exocrine function. Firstly, the expression profiles of MNK1 protein and gene in the tissues and organs of dairy cows were measured using immunohistochemistry and RT-qPCR methods. Next, an in vitro model of cultured Holstein dairy calf pancreatic acinar cells was used to detect the role of MNK1 during pancreatic enzymes release which is stimulated by leucine. Cells were incubated in culture medium containing L-leucine (0.45 mM) for 180 min, and samples were collected hourly, with the control not containing L-leucine (0 mM). MNK1 was expressed at very high levels in the pancreatic tissue of dairy cows. Leucine supplementation increased the α-amylase level but not lipase level at three time-points (60, 120, and 180 min), and the interaction between treatments and times was significant only for α-amylase. Leucine treatment enhanced (P < 0.05) the phosphorylation of MNK1 and eIF4E. In addition, inhibition of MNK1 decreased leucine-mediated α-amylase and lipase release (P < 0.05) and the phosphorylation of Mnk1 and eIF4E but did not affect (P > 0.05) the phosphorylation of the mTOR signalling pathway factors 4EBP1 and S6K1. In summary, MNK1 is a key regulator of pancreatic exocrine function, which is regulated by leucine in the pancreas of dairy cows.

Feeding amylolytic and proteolytic exogenous enzymes: Effects on nutrient digestibility, ruminal fermentation, and performance in dairy cows

Exogenous enzymes are added to diets to improve nutrient utilization and feed efficiency. A study was conducted to evaluate the effects of dietary exogenous enzyme products with amylolytic (Amaize, Alltech) and proteolytic (Vegpro, Alltech) activity on performance, excretion of purine derivatives, and ruminal fermentation of dairy cows. A total of 24 Holstein cows, 4 of which were ruminally cannulated (161 ± 88 d in milk, 681 ± 96 body weight, and 35.2 ± 5.2 kg/d of milk yield), were blocked by milk yield, days in milk, and body weight, and then distributed in a replicated 4 × 4 Latin square design. Experimental periods lasted 21 d, of which the first 14 d were allowed for treatment adaptation and the last 7 d were used for data collection. Treatments were as follows: (1) control (CON) with no feed additives, (2) amylolytic enzyme product added at 0.5 g/kg diet dry matter (DM; AML), (3) amylolytic enzyme product at 0.5 g/kg of diet DM and proteolytic enzyme product at 0.2 g/kg of diet DM (low level; APL), and (4) amylolytic enzyme products added at 0.5 g/kg diet DM and proteolytic enzyme product at 0.4 g/kg of diet DM (high level; APH). Data were analyzed using the mixed procedure of SAS (version 9.4; SAS Institute Inc.). Differences between treatments were analyzed by orthogonal contrasts: CON versus all enzyme groups (ENZ); AML versus APL+APH; and APL versus APH. Dry matter intake was not affected by treatments. Sorting index for feed particles with size <4 mm was lower for ENZ group than for CON. Total-tract apparent digestibility of DM and nutrients (organic matter, starch, neutral detergent fiber, crude protein, and ether extract) were similar between CON and ENZ. Starch digestibility was greater in cows fed APL and APH treatments (86.3%) compared with those in the AML group (83.6%). Neutral detergent fiber digestibility was greater in APH cows compared with those in the APL group (58.1 and 55.2%, respectively). Ruminal pH and NH₃-N concentration were not affected by treatments. Molar percentage of propionate tended to be greater in cows fed ENZ treatments than in those fed CON. Molar percentage of propionate was greater in cows fed AML than those fed the blends of amylase and protease (19.2 and 18.5%, respectively). Purine derivative excretions in urine and milk were similar in cows fed ENZ and CON. Uric acid excretion tended to be greater in cows consuming APL and APH than in those in the AML group. Serum urea N concentration tended to be greater in cows fed ENZ than in those fed CON. Milk yield was greater in cows fed ENZ treatments compared with CON (32.0, 33.1, 33.1, and 33.3 kg/d for CON, AML, APL, and APH, respectively). Fat-corrected milk and lactose yields were higher when feeding ENZ. Feed efficiency tended to be greater in cows fed ENZ than in those fed CON. Feeding ENZ benefited cows' performance, whereas the effects on nutrient digestibility were more pronounced when the combination of amylase and protease was fed at the highest dose.

Effects of hindgut acidosis on inflammation, metabolism, and productivity in lactating dairy cows fed a high-fiber diet

Hindgut acidosis (HGA) may cause or contribute to the inflammatory state of transition dairy cows by compromising the intestinal barrier. Previous experiments isolating the effects of HGA on inflammatory metrics have generated inconsistent results, which may be explained by acclimation to low- versus high-starch diets. Thus, study objectives were to evaluate the effects of HGA in cows acclimated to a high-fiber diet. Ten rumen-cannulated Holstein cows (38 ± 5 kg/d milk yield; 243 ± 62 d in milk; 1.6 ± 1.1 parity; 663 ± 57 kg of body weight) were enrolled in a study with 2 experimental periods (P). Before P1, all cows were acclimated to a high-fiber, low-starch diet (50% neutral detergent fiber, 15% starch) for 17 d. During P1 (4 d), baseline data were collected for use as covariates. During P2 (7 d), cows were assigned to 1 of 2 abomasal infusion treatments: (1) control (CON; 1.5 L of H₂O/infusion; n = 4) or (2) starch infused (ST; 1 kg of corn starch + 1.5 L of H₂O/infusion; n = 6). All cows were infused with their respective treatments every 6 h daily at 0000, 0600, 1200, and 1800 h, such that ST cows received a total of 4 kg of corn starch/d. Starch infusions successfully induced HGA, as indicated by a marked decrease in fecal pH (1.2 units) relative to CON. However, in contrast to our assumptions, infusing starch had no deleterious effects on milk yield, energy-corrected milk, or voluntary dry matter intake during P2. Milk protein, lactose, their yields, fat yield, and somatic cell score remained unaffected by starch infusions, whereas milk fat content and urea nitrogen were decreased in ST relative to CON (8 and 17%, respectively). Overall, circulating glucose and β-hydroxybutyrate concentrations remained similar between treatments, but starch infusions decreased nonesterified fatty acids on d 3 relative to CON. Blood urea nitrogen decreased throughout P2 in ST (38%) relative to CON. In contrast to our hypothesis, HGA did not alter circulating serum amyloid A or lipopolysaccharide binding protein, nor did it affect rectal temperature. In summary, HGA moderately altered metabolism but did not affect production or elicit an inflammatory response in lactating dairy cows previously acclimated to a high-fiber diet.

Pregnancy Toxemia in Ewes: A Review of Molecular Metabolic Mechanisms and Management Strategies

Pregnancy toxemia is a nutritional metabolic disease during late gestation in small ruminants. The condition is characterized by disorders in carbohydrate and fat metabolism. Obese and multiparous ewes are particularly susceptible to pregnancy toxemia, which may lead to maternal death, abortion, or premature birth. Highly productive multiparous meat ewes are major breeding animals, which has led to an increased incidence of the disease. However, the pathogenesis of pregnancy toxemia remains unclear and adequate disease prevention and treatment strategies are absent. Investigating the pathogenesis of pregnancy toxemia, especially the metabolic pathways of hepatic lipids, is key to an improved understanding of the condition. This review provides a snapshot of the genes that are associated with lipid metabolism in the ovine liver, including genes involved in fatty acid oxidation, acetyl coenzyme metabolism, and triglyceride synthesis; describes the interrelationships between these genes; and summarizes the diagnosis, prevention, and treatment of pregnancy toxemia.

Effects of long-term postgastric infusion of casein or glutamic acid on small intestinal starch digestion and energy balance in cattle

The objective of this experiment was to evaluate effects of postruminal flows of casein or glutamic acid on small intestinal starch digestion and to quantify changes in energy and nutrient balance. Twenty-four steers (body weight = 179 ± 4 kg) were duodenally infused with raw cornstarch (1.46 ± 0.04 kg/d) and either 413 ± 7.0 g casein/d, 121 ± 3.6 g glutamic acid/d or water (control). Measures of small intestinal starch digestion and nutrient excretion were collected across 4 d after 42 d of infusion and measures of respiration via indirect calorimetry were collected across 2 d after 48 d of infusion. Ileal starch flow was least among calves provided casein, but ileal starch flow was not different between glutamic acid or control. Small intestinal starch digestion tended to be greatest among calves provided casein, least for glutamic acid and intermediate for control. Casein increased ileal flow of ethanol soluble oligosaccharides compared to glutamic acid and control. Large intestinal starch digestion was not different among treatments. By design, N intake was greatest among cattle provided casein, intermediate among calves provided glutamic acid and least for control. Nitrogen retention was greater in response to casein compared to control and glutamic acid. Intake of gross energy from feed was similar across treatments, and gross energy from infusate was greatest for casein, intermediate for glutamic acid and least for control. Variation in gross energy intake from feed resulted in no difference in overall gross energy intake across treatments. Similar to measures of small intestinal starch digestion and N retention, casein increased calories of digestible energy and metabolizable energy, compared to glutamic acid and control, which did not differ. Postruminal infusions did not influence methane production, but heat production was greatest in steers infused with casein, intermediate for steers provided glutamic acid, and least for control. Overall, amounts of energy retained by casein tended to be nearly 34% greater than control, but glutamic acid had no impact on energy balance. Improvement in small intestinal starch digestion in response to casein increased energy and N retained; however, glutamic acid did not influence small intestinal starch digestion and energy or N balance in cattle, which seems to suggest that responses in small intestinal starch digestion to greater postruminal flows of glutamic acid become refractory across greater durations of time.

Free Amino Acid-Enriched Diets Containing Rapidly but Not Slowly Digested Carbohydrate Promote Amino Acid Absorption from Intestine and Net Fluxes across Skeletal Muscle of Pigs

BACKGROUND

The approach to matching appropriate carbohydrates alongside free amino acids to achieve optimal muscle growth remains unclear.

OBJECTIVES

We investigated whether the consumption of a diet containing rapidly digested carbohydrate and free amino acids can enhance intestinal absorption and muscular uptake of amino acids in pigs.

METHOD

Twelve barrows (28 kg; 11 wk old) with catheters installed in the portal vein, mesenteric vein, femoral artery, and femoral vein were randomly assigned to consume 1 of 2 free amino acid-enriched diets (3.34%) containing rapidly [waxy corn starch (WCS)] or slowly [pea starch (PS)] digested carbohydrate for 27 d. Blood was collected to determine the fluxes of plasma glucose and amino acids across the portal vein and the hindlimb muscle. Dietary in vitro carbohydrate digestive rates were also determined. Data were analyzed using repeated-measures (time × group) ANOVA.

RESULTS

Carbohydrate in vitro cumulative digestibility at 30 and 240 min was 69.00% and 95.25% for WCS and 23.25% and 81.15% for PS, respectively. The animal experiment presented WCS increased individual amino acids (lysine, 0.67 compared with 0.53 mmol/min; threonine, 0.40 compared with 0.29 mmol/min; isoleucine, 0.33 compared with 0.22 mmol/min; glutamate, 0.51 compared with 0.35 mmol/min; and proline, 0.51 compared with 0.27 mmol/min), essential amino acid (EAA; 3.26 compared with 2.65 mmol/min), and branched-chain amino acid (BCAA; 0.86 compared with 0.65 mmol/min) fluxes across the portal vein during 8 h postprandial, as well as individual amino acids (isoleucine, 0.08 compared with 0.02 mmol/min; leucine, 0.06 compared with 0.02 mmol/min; and glutamine, 0.44 compared with 0.25 mmol/min), EAA (0.50 compared with 0.21 mmol/min), and BCAA (0.17 compared with 0.06 mmol/min) net fluxes across the hindlimb muscle during 8 h postprandial compared with PS (P < 0.05).

CONCLUSIONS

A diet containing rapidly digested carbohydrate and free amino acids can promote intestinal absorption and net fluxes across hindlimb muscle of amino acids in pigs.

Physicochemical Changes of Heat-Treated Corn Grain Used in Ruminant Nutrition

Cereal grain is processed using different combinations of heat, moisture, time, and mechanical action in order to improve its digestibility. The objective of the present research was to quantitatively represent the physicochemical properties of raw and processed starch using an in vitro methodology, as well as to describe the changes that occurred after heat treatment, such as pelleting, steam flaking, micronization, and extrusion of corn. Based on the obtained results, pelleting, steam flaking, and micronization can be considered as mild heat treatment methods, whereas extrusion proved to be a severe heat treatment method. Analysis of functional and pasting properties implied a possible interaction between the degraded components in the steam-flaked sample, as well as in the micronized sample, through to a lesser extent. Additionally, the occurrence of dextrins was noted after extrusion. The obtained results indicate the existence of significant differences in the physicochemical properties of corn starch depending on the heat treatment applied, which could possibly affect rumen starch degradation traits.

Short Communication: Prediction of Methane per Unit of Dry Matter Intake in Growing and Finishing Cattle from the Ratio of Dietary Concentrations of Starch to Neutral Detergent Fiber Alone or in Combination with Dietary Concentration of Ether Extract

Previous research demonstrated that a fixed value of 0.2433 (SE = 0.0134) Mcal of CH₄/kg of dry matter intake (DMI) could be used to predict CH₄ production with accuracy and precision on par with similar equations in the literature. Slope bias was substantially less for the fixed-coefficient equation than noted for the other DMI- or gross energy intake (GEI)-based equations, but mean bias was substantially greater, presumably reflecting the failure of the fixed-coefficient approach to account for dietary factors that affect CH₄ production. In this article, we report on the use of the dietary ratio of concentrations of starch to neutral detergent fiber (NDF) and dietary ether extract (EE) concentration to improve the accuracy and precision of the fixed-coefficient equation. The same development data set used to create the fixed-coefficient equation was used in the present study, which included 134 treatment means from 34 respiration calorimetry studies. Based on stepwise regression with dietary NDF, starch, crude protein, EE, and the starch:NDF ratio as possible dependent variables, the starch:NDF ratio and EE were the only dietary variables selected (P ≤ 0.15). The study-adjusted relationship with the starch:NDF ratio (r² = 0.673; root mean square error [RMSE] = 0.0327) was: Mcal of CH₄/kg of DMI = 0.2883 − 0.03474 × starch:NDF; whereas the relationship with a model that included both starch:NDF ratio and dietary EE (r² = 0.738; RMSE = 0.0315) was: Mcal of CH₄/kg of DMI = 0.3227 − 0.0334 × starch:NDF − 0.00868 × % EE. A previously published independent data set with 129 treatment means from 30 respiration calorimetry studies was used to evaluate these two equations, along with two additional equations in which g/d of CH₄ was predicted directly from DMI, starch:NDF ratio, and/or dietary EE. The two Mcal of CH₄/kg of DMI equations had superior fit statistics to the previously published 0.2433 Mcal of CH₄/kg of DMI equation, with a substantial decrease in mean bias and improved concordance correlation coefficients. Moreover, the Mcal of CH₄/kg of DMI equations resulted in improved fit relative to direct prediction of g/d of CH₄ from DMI, the starch:NDF ratio, and % EE. Based on these results, further evaluation of the dietary ratio of starch-to-NDF concentrations and EE concentration to predict methane production per unit DMI in beef cattle is warranted.

Feedlot diets containing different starch levels and additives change the cecal proteome involved in cattle's energy metabolism and inflammatory response

Diets for feedlot cattle must be a higher energy density, entailing high fermentable carbohydrate content. Feed additives are needed to reduce possible metabolic disorders. This study aimed to analyze the post-rumen effects of different levels of starch (25%, 35%, and 45%) and additives (monensin or a blend of essential oils and exogenous α-amylase) in diets for Nellore feedlot cattle. The cecum tissue proteome was analyzed via two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and then differentially expressed protein spots were identified with liquid chromatography–tandem mass spectrometry (LC–MS/MS). The use of blends of essential oils associated with α-amylase as a feed additive promoted the upregulation of enzymes such as triosephosphate isomerase, phosphoglycerate mutase, alpha-enolase, beta-enolase, fructose-bisphosphate aldolase, pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), l-lactate dehydrogenase B, l-lactate dehydrogenase A chain, l-lactate dehydrogenase, and ATP synthase subunit beta, which promote the degradation of carbohydrates in the glycolysis and gluconeogenesis pathways and oxidative phosphorylation, support pyruvate metabolism through the synthesis of lactate from pyruvate, and participate in the electron transport chain, producing ATP from ADP in the presence of a proton gradient across the membrane. The absence of proteins related to inflammation processes (leukocyte elastase inhibitors) in the cecum tissues of animals fed essential oils and amylase may be because feed enzymes can remain active in the intestine and aid in the digestion of nutrients that escape rumen fermentation; conversely, the effect of monensin is more evident in the rumen and less than 10% results in post-ruminal action, corroborating the hypothesis that ionophore antibiotics have a limited effect on the microbiota and intestinal fermentation of ruminants. However, the increase in starch in these diets promoted a downregulation of enzymes linked to carbohydrate degradation, probably caused by damage to the cecum epithelium due to increased responses linked to inflammatory injuries.

Small intestinal morphology and sugar transporters expression when consuming diets of different energy levels: comparison between Tibetan and small-tailed Han sheep

Some non-structural carbohydrates, especially starch, escape ruminal fermentation, are converted into glucose, and are absorbed from the small intestine. This glucose provides an important source of energy, and its usage is more efficient than glucose from carbohydrates which are fermented as short chain fatty acids in the rumen and, subsequently, undergo hepatic gluconeogenesis. Tibetan sheep graze on the harsh Qinghai-Tibetan Plateau (QTP) all year round and their carbohydrate and energy intakes fluctuate greatly with seasonal forage availability. Consequently, a high capacity to absorb glucose from the small intestine would be particularly beneficial for Tibetan sheep to allow them to cope with the inconsistent dietary intakes. This study examined how the small intestinal morphology and sugar transporters' expression of Tibetan and Small-tailed Han (Han) sheep respond to fluctuating energy intakes under the harsh conditions of the QTP. Han sheep graze on the QTP only in summer and are generally raised in feedlots. Twenty-four Tibetan sheep and 24 Han sheep, all wethers, were assigned randomly to four groups (n = 6 per breed/group), with each group offered a diet differing in digestible energy content: 8.21, 9.33, 10.45 and 11.57 MJ/kg DM. After 49 d, all sheep were slaughtered, tissues of the small intestine were collected, and measurements were made of the morphology and glucose transporters and the related regulation gene expressions. At intakes of low energy levels, Tibetan sheep had a greater villus surface area in the duodenum, jejunum and ileum and higher mRNA expression of sodium-dependent glucose transporter 1 in the duodenum and ileum (P < 0.05) than Han sheep. In the glucose transporter 2 (GLUT2) mediated glucose absorption pathway, Tibetan sheep had higher GLUT2 and taste receptor family 1 member 2 and 3 mRNA expressions than Han sheep in the duodenum, jejunum and ileum (P < 0.05). We concluded that the differences between breeds indicated a greater glucose absorption capacity in the small intestine of Tibetan than Han sheep, which would confer an advantage to Tibetan over Han sheep to an inconsistent energy intake on the harsh QTP. These findings suggested that ruminants raised under harsh environmental conditions with highly fluctuating dietary intakes, as is often the case in grazing ruminants worldwide, are able to absorb glucose from the small intestine to a greater extent than ruminants raised under more moderate conditions.

Limiting factors for milk production in dairy cows: perspectives from physiology and nutrition

Milk production in dairy cows increases worldwide since many decades. With rising milk yields, however, potential limiting factors are increasingly discussed. Particularly, the availability of glucose and amino acids is crucial to maintain milk production as well as animal health. Limitations arise from feed sources, the rumen and digestive tract, tissue mobilization, intermediary metabolism and transport, and the uptake of circulating nutrients by the lactating mammary gland. The limiting character can change depending on the stage of lactation. Although physiological boundaries are prevalent throughout the gestation-lactation cycle, limitations are aggravated during the early lactation period when high milk production is accompanied by low feed intake and high mobilization of body reserves. The knowledge about physiological constraints may help to improve animal health and make milk production more sustainably. The scope of this review is to address contemporary factors related to production limits in dairy cows from a physiological perspective. Besides acknowledged physiological constraints, selected environmental and management-related factors affecting animal performance and physiology will be discussed. Potential solutions and strategies to overcome or to alleviate these constraints can only be presented briefly. Instead, they are thought to address existing shortcomings and to identify possibilities for optimization. Despite a scientific-based view on physiological limits, we should keep in mind that only healthy animals could use their genetic capacity and produce high amounts of milk.

Palm kernel cake in high-concentrate diets improves animal performance without affecting the meat quality of goat kids

Context Goat farming is an important socio-economic activity. The feedlot system allows the finishing of the animals in short periods through use of concentrated diets; however, these diets increase the system’s production costs. Palm kernel cake (PKC) has proved to be a good alternative feed source in diets for cattle and sheep because of its nutritional characteristics and potential to reduce production costs. Aim This experiment aimed to evaluate the effect of high-concentrate diets with the inclusion of PKC on carcass traits and meat quality of feedlot goat kids. Methods Thirty-two crossbred, castrated Boer goat kids, 4 months old and of average initial body weight 19.65±3.00kg, were used in the study. The animals were assigned to treatments in a completely randomised design, with four experimental diets containing PKC at 0%, 12%, 24%, and 36% on a dry matter basis. Measurements included total weight gain at slaughter, quantitative and sensory meat characteristics, and fatty acid profile. Key results A quadratic effect (P&lt;0.05) on total weight gain, and on meat marbling, lightness, and yellowness, was observed. The highest total weight gain and marbling were recorded with the diet containing 12% PKC. Loin eye area was also highest at 12% PKC, then decreased, whereas protein content and shear force increased (P&lt;0.05) at the higher PKC levels. Diet affected (P&lt;0.05) saturated, monounsaturated, and polyunsaturated fatty acids. No effect was observed from the inclusion of PKC on sensory attributes or on nutritional quality of the lipid fraction of the meat. Conclusion It is recommended the use up to 12% of this alternative source of nutrients, owing to the higher total weight gain and improved quantitative aspects of the goat kids’ meat such as marbling and loin eye area. Implications High-concentrate diets and the use of by-products for animal nutrition have become common in animal production systems. The increasing use of PKC in animal nutrition leads us to determine the best dietary inclusion level, avoiding undesirable production or product quality characteristics.

Effects of corn processing and cattle size on total tract digestion and energy and nitrogen balance

This study used 18 calves (295 ± 29 kg) and 18 yearlings (521 ± 29 kg) fed whole, cracked, or steam-flaked corn (SFC) to evaluate nutrient digestion and energy balance across different types of processed corn and sizes of cattle. Cattle were fed a diet comprised of 75% corn (dry matter [DM]-basis) from whole, cracked, or SFC to 2.5-times maintenance energy requirements. Subsequently, cattle were placed in individual stanchions, and urine and feces were collected together with measures of gas production via indirect calorimetry. Data were analyzed using the MIXED procedure of SAS. There was no interaction between corn processing and cattle size (P ≥ 0.40). Time spent ruminating (min/d) and rumination rate (min/kg DM intake [DMI]) were not affected by corn processing or cattle size. The eating rate (min/kg DMI) was faster (P < 0.01) for yearlings compared with calves. Total tract starch digestion was greatest (P = 0.01) for cattle fed SFC (97.5%), intermediate in cattle fed cracked (92.4%), and least in cattle fed whole corn (89.5%). Dietary digestible energy and metabolizable energy (Mcal/kg DMI) were greater (P ≤ 0.05) for cattle fed SFC compared with cracked or whole. A greater proportion of digestible energy was lost to heat production (P = 0.01) in cattle fed whole corn compared with cracked and tended to be greater (P = 0.08) in cattle fed SFC than cracked. Conversion of digestible energy to metabolizable energy in this study was more closely related to a dynamic model used to estimate metabolizable energy of feeds to dairy cows than to a linear model used to predict metabolizable energy of feeds to beef cattle. If library estimates of net energy for maintenance are correct, then retained energy (Mcal/d) should have been similar between each type of processed corn; however, retained energy was greater (P < 0.01) for cattle fed cracked compared with whole corn and tended to be greater (P = 0.06) compared with SFC. Yet, observed amounts of net energy based on measures of retained energy were not different (P ≥ 0.60) between cracked and SFC. Nitrogen balance was not affected (P ≥ 0.30) by corn processing or cattle size, although cattle fed cracked had numerically greater (P ≤ 035) N retention. These data indicate that physical processing of corn provides greater net energy to cattle in comparison to whole corn.

Effect of flaking on the digestibility of corn in ruminants

In this study, we aimed to assess the effect of flaking on the nutrient digestibility of corn grain in ruminants. In this regard, in vitro rumen fermentation, in situ rumen degradability, and in vivo metabolic experiments were performed. The automated gas production technique was used for the in vitro fermentation experiments. Six types of corn flakes with various degrees of gelatinization (32%, 41%, 48%, 66%, 86%, and 89%) were ground and incubated in rumen fluid to measure rumen fermentation characteristics and digestion rate. The in situ degradability of ground corn, whole corn, and corn flakes with 62% and 66% gelatinization was measured by incubation in the rumen of two cannulated Holstein cows. In vivo metabolic experiments were performed using 12 crossbred goats (29.8 ± 4.37 kg) using a 3 × 3 Latin square design. The dietary treatments consisted of ground corn and flaked corn with 48% or 62% gelatinization. In vitro experiments showed that as the degree of gelatinization increased, the digestion rate increased linearly, while the discrete lag time decreased linearly (p < 0.05). The effective rumen dry matter degradability, determined by in situ fermentation, was 37%p lower in corn flakes than ground corn, assuming a passage rate of 6%/h (p < 0.01), and there was no difference between the two flakes. In the in vivo experiment, there was no difference in dry matter intake, average daily gain, feed efficiency, and nitrogen utilization among the treatment groups (p > 0.05); however, the crude fat digestibility was lower for corn flakes than for ground corn (p < 0.05). To summarize, the rate of fermentation of corn flakes increased as the degree of gelatinization increased. However, non-ground corn flakes had lower rumen digestibility and did not improve in vivo apparent nutrient digestibility, compared with ground corn. In contrast to the assumption that flaked corn provides more energy to ruminant animals than ground corn, we conclude that the digestibility and energy value of corn flakes are lower than those of ground corn if mastication does not sufficiently reduce the particle size of corn flakes.

High-level dietary crude protein decreased backfat thickness and increased carcass yield score in finishing Hanwoo beef cattle (Bos taurus coreanae)

Recently, a high level of dietary crude protein (CP) has become of interest as a possible practice to improve the carcass quality of beef cattle, and its level has been increasing in the field. However, there is little scientific evidence that supports this. This study was conducted to test whether a high dietary CP level would improve growth performance, body metabolism, and carcass traits in Hanwoo beef cattle. A total of 32 Hanwoo finishing beef cattle (18 multiparous cows, six heifers, and eight steers) participated in a 12-weeks feeding trial. Two kinds of total mixed rations were prepared to contain two different CP; 156 g/kg for the control (CON) and 173 g/kg of CP for the treatment (HCP), while maintaining a similar level of metabolizable energy. The experiment was ended when more than half of the steers reached the target body weight (730 kg). Blood was collected at the end of the experiment. After harvesting, the carcass trait was evaluated at the slaughterhouse according to Korean standards. The carcass yield score and grade were also calculated based on revised criteria. Overall, dry matter intake, average daily gain, blood metabolites concentration, and the carcass traits, except for backfat thickness and the yield score, did not differ between the treatments. The HCP had lower backfat thickness than those of CON. There was no difference in the carcass yield grade, but the yield score was higher in the HCP treatment. According to the newly revised carcass grading criteria, both yield score and grade were higher in HCP than in CON. Increasing CP supply decreased the carcass’s backfat thickness without altering growth performance and body metabolism, resulting in improved yield score and grade. Therefore, feeding a high CP diet may be beneficial in the farm income, although it may also increase feed cost and nitrogen excretion to the environment.

Flake density and starch retrogradation influence in situ ruminal degradability characteristics of steam-flaked corn and predicted starch digestibility and energetic efficiency

Five ruminally cannulated steers (body weight = 390 ± 7.86 kg) were used in two experiments to evaluate the effects of flake density and starch retrogradation on in situ ruminal degradation of steam-flaked corn. In experiment 1, sifted flakes with flake densities of 257, 296, 335, 373, and 412 g/L (enzymatic starch availabilities: 87%, 76%, 66%, 43%, and 49%, respectively) were evaluated in a randomized complete block design experiment. In experiment 2, the experimental design was a randomized complete block design with a 3 × 2 factorial arrangement of treatments. Three steam-flaked corn fractions corresponding to different particle sizes were used: flakes + fines (not sifted; >4 and <4 mm), sifted flakes (>4 mm), and sifted fines (<4 mm). Particle size fractions were stored for 3 d at either 23 °C or 55 °C (starch availabilities averaged across particle sizes: 53.3% and 25.5%, respectively) in heat-sealed foil bags. Samples were ruminally incubated for 0, 3, 6, 12, 24, 48, 72, or 96 h. Degradation data were modeled to obtain the rate and extent of degradation and passage rate was set to 6% per hour. In experiment 1, the rate of degradation decreased linearly (P < 0.01) and in situ ruminal dry matter (DM) degradability decreased linearly (P < 0.01) from 78.9% to 57.3% as flake density increased from 257 to 412 g/L. In experiment 2, storage of steam-flaked corn samples at 55 °C for 3 d decreased (P < 0.01) the rate of degradation by 37.6% across all particle sizes. Storing samples at 55 °C for 3 d decreased (P < 0.01) in situ ruminal DM degradability of flakes + fines, sifted flakes, and sifted fines by 20.9%, 22.6%, and 14.7%, respectively. Using data from experiment 1 and 2, enzymatic starch availability of sifted flakes was positively correlated (R2 = 0.97; P < 0.01) with in situ ruminal DM degradability. The results demonstrate that decreased starch availability resulting from either starch retrogradation or increased flake density is associated with decreased ruminal digestibility. Decreases in starch availability and in situ ruminal degradability may indicate that increasing flake density or starch retrogradation could potentially alter the site of digestion in cattle. Using prediction equations, decreases in ruminal starch digestibility of steam-flaked corn caused by increasing flake density or increasing starch retrogradation could increase energetic efficiency, depending on the rate of passage and if small intestinal starch digestibility is maintained.

Abomasal infusion of corn starch and β-hydroxybutyrate in early-lactation Holstein-Friesian dairy cows to induce hindgut and metabolic acidosis

The objectives of this study were to induce hindgut and metabolic acidosis via abomasal infusion of corn starch and β-hydroxybutyrate (BHB), respectively, and to determine the effects of these physiological states in early-lactation dairy cows. In a 6 × 6 Latin square design, 6 rumen-fistulated Holstein-Friesian dairy cows (66 ± 18 d in milk) were subjected to 5 d of continuous abomasal infusion treatments followed by 2 d of rest. The abomasal infusion treatments followed a 3 × 2 factorial design, with 3 levels of corn starch and 2 levels of BHB. The infusions were water as control, 1.5 kg of corn starch/d, 3.0 kg of corn starch/d, 8.0 mol BHB/d, 1.5 kg of corn starch/d + 8.0 mol BHB/d, or 3.0 kg of corn starch/d + 8.0 mol BHB/d. A total mixed ration consisting of 35.0% grass silage, 37.4% corn silage, and 27.6% concentrate (on a dry matter basis) was fed at 90% of ad libitum intake of individual cows. The experiment was conducted in climate respiration chambers to facilitate determination of energy and N balance. Fecal pH decreased with each level of corn starch infused into the abomasum and was 6.49, 6.00, and 5.15 with 0.0, 1.5, and 3.0 kg of corn starch/d, respectively, suggesting that hindgut acidosis was induced with corn starch infusion. No systemic inflammatory response was observed and the permeability of the intestine or hindgut epithelium was not affected by the more acidic conditions. This induced hindgut acidosis was associated with decreased digestibility of nutrients, except for crude fat and NDF, which were not affected. Induced hindgut acidosis did not affect milk production and composition and energy balance, but increased milk N efficiency. Abomasal infusion of BHB resulted in a compensated metabolic acidosis, which was characterized by a clear disturbance of acid-base status (i.e., decreased blood total CO₂, HCO₃, and base excess, and a tendency for decreased urinary pH), whereas blood pH remained within a physiologically normal range. Abomasal infusion of BHB resulted in increased concentrations of BHB in milk and plasma, but both remained well below the critical threshold values for subclinical ketosis. Induced compensated metabolic acidosis, as a result of abomasally infused BHB, increased energy retained as body fat, did not affect milk production and composition or inflammatory response, but increased intestinal permeability.

Blend of Essential Oils Supplemented Alone or Combined with Exogenous Amylase Compared with Virginiamycin Supplementation on Finishing Lambs: Performance, Dietary Energetics, Carcass Traits, and Nutrient Digestion

Simple Summary

Antibiotics have been extensively used as growth promoters in livestock, but current interests are focused on limiting the use of conventional antibiotics as feed additives in livestock production. Essential oil compounds belong to a “generally-recognized-as-safe” category of feed additives that may serve as alternatives to conventional antibiotics used as growth promoters. In this study, dietary supplementation of finishing lambs with essential oils alone, or combined with exogenous enzymes, improved dietary energy utilization and meat production in a manner comparable to that of the antibiotic virginiamycin.

Abstract

Two experiments were conducted to compare a supplemental blend of essential oils alone (EO) or combined with enzymes (EO + ENZ) versus virginiamycin (VM), on characteristics of growth performance (Exp. 1) and digestion (Exp. 2) in finishing lambs. Lambs were fed a high-energy finishing diet supplemented with: (1) no supplement (control); (2) 150 mg supplemental EO; (3) 150 mg supplemental EO plus 560 mg alpha-amylase (EO + ENZ); and 4) 25 mg VM. Compared with the control, growth performance response to EO and VM were similar, enhancing (5.7%, p < 0.05) feed efficiency and observed dietary net energy. Compared with control, supplementation with EO + ENZ tended (p = 0.09) to increase dry matter intake (6.8%), improving (p < 0.05) weight gain and feed efficiency (10.4 and 4.4%, respectively). Dietary energy utilization was greater (2.7%, p < 0.05) for EO and VM than EO + ENZ. Treatment effects on the carcass and visceral mass were small, but additive supplementation decreased (p ≤ 0.03) the relative weight of the intestines. There were no treatment effects on measures of digestion nor digestible energy of the diet. Supplemental EO may be an effective alternative to VM in high-energy finishing diets for feedlot lambs. Combination EO + ENZ may further enhance dry matter intake, promoting increased weight gain.

Corn versus Barley in Finishing Diets: Effect on Steer Performance and Feeding Behavior

This study evaluated the effects of barley and corn finishing rations on feedlot performance and behavior of steers. Feedlot rations in this study were comprised of a main concentrate of either corn or barley. Steers were fed in a GrowSafe system to measure individual animal intake and behavior. Weight gain, average daily gain (ADG), and gain:feed were measured for each steer. Feeding behavior including time spent eating (min/day), visits per day, time per visit (min), eating rate (g/min), intake (kg/day), and intake per visit (g) were measured for each individual. Corn-fed steers had greater ADG (p < 0.01) and heavier hot carcass weights (HCW; p < 0.01). In addition, corn fed steers had a higher yield grade than barley fed steers (p < 0.01). No treatment effects (p ≥ 0.11) were observed for time spent eating, visits per day, time per visit, eating rate, intake g/kg body weight, or intake per visit. Although corn-fed steers had a greater ADG and HCW than barley-fed steers, they tended to consume more feed (p = 0.06). Depending on the difference of costs associated with feeding corn or barley, barley could be a potential high-quality feed source in beef cattle finishing rations.

Metabolic and Productive Response and Grazing Behavior of Lactating Dairy Cows Supplemented with High Moisture Maize or Cracked Wheat Grazing at Two Herbage Allowances in Spring

Simple Summary

Energy supplements such as high moisture maize or cracked wheat increase total dry matter intake (DMI) and dairy cow performance compared to pasture-only diets. However, the effectiveness of such a feeding strategy depends upon the level of herbage allowance (HA). In this study, increasing HA from 20 to 30 kg DM/cow had no effect on milk production but increased the concentration of urea in milk and plasma regardless of the type of energy supplement offered to grazing dairy cows. These results demonstrate that in high-quality pasture, low HA is appropriate to improve milk production performance per cow and per hectare.

Abstract

The aim was to determine the effect of the herbage allowance (HA) and supplement type (ST) on dry matter intake (DMI), milk production and composition, grazing behavior, rumen function, and blood metabolites of grazing dairy cows in the spring season. Experiment I: 64 Holstein Friesian dairy cows were distributed in a factorial design that tested two levels of daily HA (20 and 30 kg of dry matter (DM) per cow) and two ST (high moisture maize (HMM) and cracked wheat (CW)) distributed in two daily rations (3.5 kg DM/cow/day). Experiment II: four mid-lactation rumen cannulated cows, supplemented with either HMM or CW and managed with the two HAs, were distributed in a Latin square design of 4 × 4, for four 14-d periods to assess ruminal fermentation parameters. HA had no effect on milk production (averaging 23.6 kg/day) or milk fat and protein production (823 g/day and 800 g/day, respectively). Cows supplemented with CW had greater protein concentration (+1.2 g/kg). Herbage DMI averaged 14.17 kg DM/cow.day and total DMI averaged 17.67 kg DM/cow.day and did not differ between treatments. Grazing behavior activities (grazing, rumination, and idling times) and body condition score (BCS) were not affected by HA or ST. Milk and plasma urea concentration increased under the high HA (+0.68 mmol/L and +0.90 mmol/L, respectively). Cows supplemented with HMM had lower milk and plasma urea concentrations (0.72 mmol/L and 0.76 mmol/L less, respectively) and tended (p = 0.054) to have higher plasma β-hydroxybutyrate. Ruminal parameters did not differ between treatments.

Diet Transition from High-Forage to High-Concentrate Alters Rumen Bacterial Community Composition, Epithelial Transcriptomes and Ruminal Fermentation Parameters in Dairy Cows

Effects of changing diet on rumen fermentation parameters, bacterial community composition, and transcriptome profiles were determined in three rumen-cannulated Holstein Friesian cows using a 3 × 4 cross-over design. Treatments include HF-1 (first high-forage diet), HC-1 (first high-concentrate diet), HC-2 (succeeding high-concentrate diet), and HF-2 (second high-forage diet as a recovery period). Animal diets contained Klein grass and concentrate at ratios of 8:2, 2:8, 2:8, and 8:2 (two weeks each), respectively. Ammonia-nitrogen and individual and total volatile fatty acid concentrations were increased significantly during HC-1 and HC-2. Rumen species richness significantly increased for HF-1 and HF-2. Bacteroidetes were dominant for all treatments, while phylum Firmicutes significantly increased during the HC period. Prevotella, Erysipelothrix, and Galbibacter significantly differed between HF and HC diet periods. Ruminococcus abundance was lower during HF feeding and tended to increase during successive HC feeding periods. Prevotellaruminicola was the predominant species for all diets. The RNA sequence analysis revealed the keratin gene as differentially expressed during the HF diet, while carbonic-anhydrase I and S100 calcium-binding protein were expressed in the HC diet. Most of these genes were highly expressed for HC-1 and HC-2. These results suggested that ruminal bacterial community composition, transcriptome profile, and rumen fermentation characteristics were altered by the diet transitions in dairy cows.

Effect of feeding dry-rolled corn or whole shelled corn during the finishing phase on growth performance and carcass characteristics

The objectives of this trial were to evaluate the effect of corn processing during the finishing phase on feedlot cattle performance and carcass characteristics. We hypothesized that steers fed dry-rolled corn would have better feed efficiency (less feed necessary to the same amount of gain) than steers fed whole shelled corn. Ninety-five backgrounded Angus-cross cattle (initial body weight [BW] = 263 ± 9.8 kg) were used in a randomized complete block design in a feedlot setting. Cattle were divided in to 3 blocks: heifers (n = 31, 4 pens; initial BW = 267 ± 1.3 kg), light steers (n = 32, 4 pens; initial BW = 253 ± 1.3 kg), and heavy steers (n = 32, 4 pens; initial BW = 279 ± 1.4 kg). Diets contained 70% corn (experimental treatment), 15% dried distiller’s grains with solubles, 7% grass hay, and 8% supplement, on a dry matter basis. Cattle were fed for 217, 224, and 231 ± 8 d for the heifer, heavy steer, and light steer blocks, respectively. Two pens within each block were randomly assigned to one of the following treatments: (1) dry-rolled corn (DRC) or (2) whole-shelled corn (WSC). Animal growth performance and carcass characteristics were analyzed using the MIXED procedure of SAS, including the fixed effect of treatment. Pen and block were included as random effects. Carcass characteristics USDA Yield Grade and Quality Grade distributions were compared using the GLIMMIX procedure of using the same model than the growth performance data. Data are presented as LSMeans. Cattle fed DRC had greater average daily gain (ADG; P = 0.02) and final BW (P < 0.01) when compared with cattle fed WSC. Even though ADG was greater for the DRC treatment, feed efficiency was similar (P = 0.45) because dry matter intake was also greater (P = 0.04) for DRC when compared with the WSC treatment. Cattle fed DRC also had greater hot carcass weight (P < 0.01), dressing percentage (P < 0.01), and Longissimus dorsi muscle area (P < 0.01) than cattle fed WSC. No differences (P ≥ 0.18) were observed for marbling score, USDA Yield Grade or USDA Quality Grade. In conclusion, feeding DRC to feedlot cattle improved ADG, hot carcass weight, and Longissimus dorsi muscle area, without affecting feed efficiency or meat quality.

Abomasal infusion of ground corn and ammonium chloride in early-lactating Holstein-Friesian dairy cows to induce hindgut and metabolic acidosis

Next to rumen acidosis, other forms of acidosis may also affect lactational performance of cows. Therefore, the effects of hindgut acidosis, induced via abomasal infusion of ground corn, and metabolic acidosis, induced via abomasal infusion of NH₄Cl, were studied in cows in early lactation. Observations were made on intake and digestibility of nutrients, lactation performance, energy and N partitioning, blood acid-base status, and rumen and hindgut fermentation characteristics. In a 6 × 6 Latin square design, 6 rumen-fistulated, second-lactation Holstein-Friesian dairy cows (48 ± 17 d in milk) were subjected to 5 d of continuous abomasal infusions of water as control, or solutions of 2.5 mol of NH₄Cl/d, 5.0 mol of NH₄Cl/d, 3.0 kg of ground corn/d, or the combination of ground corn with either of the 2 NH₄Cl levels, followed by 2 d of rest. Treatment solutions were administered via peristaltic pumps through infusion lines attached to the rumen cannula plug and an abomasal infusion line with a flexible disk (equipped with holes to allow digesta passage) to secure its placement through the sulcus omasi. A total mixed ration consisting of 70% grass silage and 30% concentrate (on dry matter basis) was fed at 95% of ad libitum intake of individual cows. The experiment was conducted in climate respiration chambers to determine feed intake, lactation performance, and energy and N balance. Abomasal infusion of NH₄Cl affected the acid-base status of the cows, but more strongly when in combination with abomasal infusion of ground corn. Metabolic acidosis (defined as a blood pH < 7.40, blood HCO₃ concentration < 25.0 mmol/L, and a negative base excess) was observed with 5.0 mol of NH₄Cl/d, 3.0 kg of ground corn/d + 2.5 mol of NH₄Cl/d, and 3.0 kg of ground corn/d + 5.0 mol of NH₄Cl/d. Metabolic acidosis was associated with decreased milk lactose content, metabolic body weight, energy retained as protein, and fecal N excretion, and increased urine N excretion, and tended to decrease intake of nutrients. Digestibility of several nutrients increased with 5.0 mol of NH₄Cl/d, likely as a result of decreased intake. Abomasal ground corn infusion resulted in hindgut acidosis, where fecal pH decreased from 6.86 without ground corn to 6.00 with ground corn, regardless of NH₄Cl level. The decrease in fecal pH was likely the result of increased hindgut fermentation, evidenced by increased fecal volatile fatty acid concentrations. Hindgut acidosis was associated with decreased digestibility of nutrients, except for starch, which increased, and crude fat, which was not affected. No systemic inflammatory response was observed, suggesting that the hindgut epithelium was not severely affected by the more acidic conditions or barrier damage. Abomasal infusion of ground corn increased milk yield, milk protein and lactose yield, fecal N excretion, N use efficiency, and total energy retained as well as energy retained in fat, and reduced milk fat content and urine N excretion.

Prenatal and Postnatal Nutrition Influence Pancreatic and Intestinal Carbohydrase Activities of Ruminants

In ruminant livestock species, nutrition can play an important role in the long-term programming of gastrointestinal function. Pancreatic and small intestinal digestive enzymes are important for postruminal digestion of carbohydrates and protein. Carbohydrases have been shown to respond to changes in the level of feed intake and the dietary inclusion of specific nutrients, including arginine, butyrate, folic acid, fructose, and leucine. Understanding how diet influences enzyme development and activity during prenatal and postnatal life could lead to the development of dietary strategies to optimize offspring growth and development to increase digestive efficiency of ruminant livestock species. More research is needed to understand how changes in fetal or neonatal carbohydrase activities in response to nutrition influence long-term growth performance and efficiency in ruminant livestock species to optimize nutritional strategies.

Effects of exogenous α-amylases, glucoamylases, and proteases on ruminal in vitro dry matter and starch digestibility, gas production, and volatile fatty acids of mature dent corn grain

Two separate experiments were carried out to evaluate the effects of incremental doses of 10 exogenous endo-acting α-amylase and exo-acting glucoamylase; 1LAT (bacterial α-amylase), 2AK, 3AC, 4Cs4, 5Trga, 6Afuga, 7Fvga, and 10Tg (fungal α-amylases, glucoamylases, and α-glucosidase), 8Star and 9Syn (fungal amylase-mixtures; experiment 1) and three exogenous proteases; 11P14L, 12P7L, and 13P30L (bacterial proteases; experiment 2) on in vitro dry matter digestibility (IVDMD) and in vitro starch digestibility (IVSD) of mature dent corn grain using a batch culture system. Incremental doses of the exogenous enzymes (0, 0.25, 0.50, 0.75, and 1.00 mg/g of dried substrate) were applied directly to the substrate (0.5 g of ground corn, 4 mm) in sextuplicate (experiment 1) or quadruplicate (experiment 2) within F57 filter bags, which were incubated at 39 °C in buffered rumen fluid for 7 h. Rumen fluid was collected 2-3 h after the morning feeding from three lactating dairy cows and pooled. Cows were consuming a midlactation total mixed ration (TMR; 1.60 Mcal/kg DM and 15.4%; net energy of lactation and crude protein, respectively). Three independent runs were carried out for each experiment. Data were analyzed as a randomized complete block design using run as the blocking factor. Dose was used as a fixed factor while run was considered a random factor. Linear, quadratic, and cubic orthogonal contrasts were also tested. In experiment 1, enzymes 2AK, 3AC, and 10Tg did not increase (P > 0.10) IVDMD and IVSD, whereas 0.25 mg of enzymes 1LAT, 5Trga, and 8Star increased (P < 0.01) IVDMD by 23%, 47%, and 62% and IVSD by 35%, 41%, and 58%, respectively, compared with the control. Enzymes 4Cs4, 6Afuga, 7Fvga, and 9Syn linearly increased IVDMD and IVSD (P < 0.01). Greatest increases in IVDMD (82.9%) and IVSD (85.9%) resulted with 1 mg of 6Afuga compared to control. In experiment 2, the lowest dose of exogenous proteases 11P14L and 12P7L increased (P < 0.01) IVDMD by 98% and 87% and IVSD by 57% and 64%, respectively, whereas the highest dose of 13P30L increased (P = 0.02) IVDMD by 44.8% and IVSD by 30%, relative to the control. In conclusion, IVSD and IVDMD were increased by one α-amylase, certain glucoamylases, and all proteases tested, with the glucoamylase 6Afuga in experiment 1 and the neutral protease 12P7L in experiment 2, increasing IVDMD and IVSD to the greater extents. Future in vivo studies are required to validate these findings before these enzyme additives can be recommended for improving the digestibility of mature dent corn grain.

Identification of a Candidate Starch Utilizing Strain of Prevotella albensis from Bovine Rumen

The inclusion of starch-rich feedstuffs, a common practice in intensive ruminant livestock production systems, can result in ruminal acidosis, a condition that can severely impact animal performance and health. One of the main causes of acidosis is the rapid accumulation of ruminal short chain fatty acids (SCFAs) resulting from the microbial digestion of starch. A greater understanding of ruminal bacterial amylolytic activities is therefore critical to improving mitigation of acidosis. To this end, our manuscript reports the identification of a candidate starch utilizer (OTU SD_Bt-00010) using batch culturing of bovine rumen fluid supplemented with starch. Based on 16S rRNA gene sequencing and metagenomics analysis, SD_Bt-00010 is predicted to be a currently uncharacterized strain of Prevotella albensis. Annotation of de novo assembled contigs from metagenomic data not only identified sequences encoding for α-amylase enzymes, but also revealed the potential to metabolize xylan as an alternative substrate. Metagenomics also predicted that SCFA end products for SD_Bt-00010 would be acetate and formate, and further suggested that this candidate strain may be a lactate utilizer. Together, these results indicate that SD_Bt-00010 is an amylolytic symbiont with beneficial attributes for its ruminant host.