Concentration and estimated flow of peptides from the rumen of dairy cattle: effects of protein quantity, protein solubility, and feeding frequency

Supplementation of Methionine Dipeptide Enhances the Milking Performance of Lactating Dairy Cows

Methionine dipeptide (Met-Met) could improve milk protein synthesis in bovine epithelia mammary cells and lactating mice, while the effects of Met-Met on lactation performance, rumen fermentation and microbiota profile in lactating dairy cows have not been explored. For this reason, 60 Chinese lactating Holstein cows were allocated into three treatment groups: control group (CON), 6 g/d methionine dipeptide group (MM), and 6.12 g/d rumen-protected methionine dipeptide group (RPMM). The experiment lasted for 10 weeks to monitor lactation performance, plasma amino acid profile and rumen fermentation parameters and microbiota profile. Results showed that MM increased the energy-corrected milk (ECM), and RPMM increased both milk yield and ECM (p < 0.05). The milk protein concentration and yield were increased by MM and RPMM (p < 0.05). The rumen fermentation showed that RPMM increased total volatile fatty acids, acetate and valerate concentrations (p < 0.05). The relative abundance of Firmicutes, including Succiniclasticum, Selenomonas and Clostridium_XlVa, were enriched and the Prevotella was decreased by RPMM (p < 0.05). In summary, daily supplementing with 6 g of MM or RPMM in lactating dairy cows could improve milk yield and both percentage and yield of milk protein, and RPMM benefited the rumen fermentation and altered the bacterial composition. These results provided the first evidence that Met-Met supplementation can improve lactation performance of dairy cows.

Regulation of Milk Protein Synthesis by Free and Peptide-Bound Amino Acids in Dairy Cows

Milk protein (MP) synthesis in the mammary gland of dairy cows is a complex biological process. As the substrates for protein synthesis, amino acids (AAs) are the most important nutrients for milk synthesis. Free AAs (FAAs) are the main precursors of MP synthesis, and their supplies are supplemented by peptide-bound AAs (PBAAs) in the blood. Utilization of AAs in the mammary gland of dairy cows has attracted the great interest of researchers because of the goal of increasing MP yield. Supplying sufficient and balanced AAs is critical to improve MP concentration and yield in dairy cows. Great progress has been made in understanding limiting AAs and their requirements for MP synthesis in dairy cows. This review focuses on the effects of FAA and PBAA supply on MP synthesis and their underlying mechanisms. Advances in our knowledge in the field can help us to develop more accurate models to predict dietary protein requirements for dairy cows MP synthesis, which will ultimately improve the nitrogen utilization efficiency and lactation performance of dairy cows.

Functional annotation of the cattle genome through systematic discovery and characterization of chromatin states and butyrate-induced variations

BACKGROUND

The functional annotation of genomes, including chromatin accessibility and modifications, is important for understanding and effectively utilizing the increased amount of genome sequences reported. However, while such annotation has been well explored in a diverse set of tissues and cell types in human and model organisms, relatively little data are available for livestock genomes, hindering our understanding of complex trait variation, domestication, and adaptive evolution. Here, we present the first complete global landscape of regulatory elements in cattle and explore the dynamics of chromatin states in rumen epithelial cells induced by the rumen developmental regulator-butyrate.

RESULTS

We established the first global map of regulatory elements (15 chromatin states) and defined their coordinated activities in cattle, through genome-wide profiling for six histone modifications, RNA polymerase II, CTCF-binding sites, DNA accessibility, DNA methylation, and transcriptome in rumen epithelial primary cells (REPC), rumen tissues, and Madin-Darby bovine kidney epithelial cells (MDBK). We demonstrated that each chromatin state exhibited specific enrichment for sequence ontology, transcription, methylation, trait-associated variants, gene expression-associated variants, selection signatures, and evolutionarily conserved elements, implying distinct biological functions. After butyrate treatments, we observed that the weak enhancers and flanking active transcriptional start sites (TSS) were the most dynamic chromatin states, occurred concomitantly with significant alterations in gene expression and DNA methylation, which was significantly associated with heifer conception rate and stature economic traits.

CONCLUSION

Our results demonstrate the crucial role of functional genome annotation for understanding genome regulation, complex trait variation, and adaptive evolution in livestock. Using butyrate to induce the dynamics of the epigenomic landscape, we were able to establish the correlation among nutritional elements, chromatin states, gene activities, and phenotypic outcomes.

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques

Nitrogen is a component of essential nutrients critical for the productivity of ruminants. If excreted in excess, N is also an important environmental pollutant contributing to acid deposition, eutrophication, human respiratory problems, and climate change. The complex microbial metabolic activity in the rumen and the effect on subsequent processes in the intestines and body tissues make the study of N metabolism in ruminants challenging compared with nonruminants. Therefore, using accurate and precise measurement techniques is imperative for obtaining reliable experimental results on N utilization by ruminants and evaluating the environmental impacts of N emission mitigation techniques. Changeover design experiments are as suitable as continuous ones for studying protein metabolism in ruminant animals, except when changes in body weight or carryover effects due to treatment are expected. Adaptation following a dietary change should be allowed for at least 2 (preferably 3) wk, and extended adaptation periods may be required if body pools can temporarily supply the nutrients studied. Dietary protein degradability in the rumen and intestines are feed characteristics determining the primary AA available to the host animal. They can be estimated using in situ, in vitro, or in vivo techniques with each having inherent advantages and disadvantages. Accurate, precise, and inexpensive laboratory assays for feed protein availability are still needed. Techniques used for direct determination of rumen microbial protein synthesis are laborious and expensive, and data variability can be unacceptably large; indirect approaches have not shown the level of accuracy required for widespread adoption. Techniques for studying postruminal digestion and absorption of nitrogenous compounds, urea recycling, and mammary AA metabolism are also laborious, expensive (especially the methods that use isotopes), and results can be variable, especially the methods based on measurements of digesta or blood flow. Volatile loss of N from feces and particularly urine can be substantial during collection, processing, and analysis of excreta, compromising the accuracy of measurements of total-tract N digestion and body N balance. In studying ruminant N metabolism, nutritionists should consider the longer term fate of manure N as well. Various techniques used to determine the effects of animal nutrition on total N, ammonia- or nitrous oxide-emitting potentials, as well as plant fertilizer value, of manure are available. Overall, methods to study ruminant N metabolism have been developed over 150 yr of animal nutrition research, but many of them are laborious and impractical for application on a large number of animals. The increasing environmental concerns associated with livestock production systems necessitate more accurate and reliable methods to determine manure N emissions in the context of feed composition and ruminant N metabolism.

Feeding value of whole raw soya beans as a protein supplement for beef cattle consuming low-quality forages

Experiments (Exp) I and II were conducted to compare raw whole soya beans (WSB), roasted (rWSB) or other protein sources as supplements of low-quality forages fed ad libitum to beef cattle, upon DM intake (DMI), ruminal and blood parameters, and animal performance. Exp I: treatments for wheat straw fed to four ruminally cannulated steers were (i) Control-WS: no supplement; (ii) WSB-WS: whole soya beans; (iii) rWSB-WS: roasted WSB; and (iv) SBM-WS: soybean meal-wheat midds mixture; all fed at 1.4 kg DM/day. Exp II: 12 steers grazed deferred grain sorghum (DS) receiving these treatments: (i) Control-DS: no supplement; (ii) WSB-DS: 1.26 kg DM/day whole soya beans; and (iii) SFM-DS: 1.35 kg DM/day of sunflower meal. In Exp I, WS DMI resulted 47, 52 and 41% greater for WSB-WS, rWSB-WS and SBM-WS, respectively, than Control-WS (p < .05). In Exp II, the DMI of DS was unaffected by supplementation; a substitution of DS by supplement was found for WSB-DS (p < .05); however, total diet and digestible DMI increased with supplementation (p < .05). Rumen pH in Exp I remained unaffected by supplementation, but N-NH3 as well as blood urea-N in Exp II increased (p < .05). In Exp II, average daily weight gains improved similarly with both supplements compared with Control-DS. Additionally, feed-to-gain ratio decreased (p < .05), being lower for WSB-DS (8.3) vs. SFM-DS (9.9). Roasting effects of WSB as a supplement for low-quality forages were not detected, and all protein sources increased total diet DMI and forage utilization. Only moderate cattle weight gains could be expected for unsupplemented DS.

Chemical and ruminal in vitro evaluation of Canadian canola meals produced over 4 years

To test the effects of year and processing plant on the nutritional value of canola meal (CM), 3 CM samples/yr were collected from each of 12 Canadian production plants over 4yr (total=144). Samples of CM were analyzed for differences in chemical composition and for in vitro ruminal protein degradability using the Michaelis-Menten inhibitor in vitro (MMIIV) method. In the MMIIV method, protein degradation rate (kd) was estimated by 2 methods: from net release (i.e., blank corrected) of (1) ammonia plus AA determined by o-phthaldialdehyde fluorescence (OPAF) assay or (2) ammonia, AA, plus oligopeptides determined by o-phthaldialdehyde absorbance (OPAA) assay; rumen-undegradable protein (RUP) was computed assuming passage rates of 0.16 and 0.06/h for, respectively, soluble and insoluble protein. Casein, solvent soybean meal (SSBM), and expeller soybean meal (ESBM) were included in all incubations as standard proteins. Differences among years and plants were assessed using the mixed procedures of SAS. Small but significant differences were found in CM among years for chemical composition, including N solubility; some of these differences may have been related to changes in our analytical methods over time. However, adjustment of degradation activity of individual in vitro incubations based on the mean degradation activity over all incubations yielded kd and RUP that did not differ by year using either assay. Simultaneously incubating CM samples from 2yr in the same in vitro runs confirmed that no year effects existed for kd or RUP. Differences existed in chemical composition of CM among the 12 processing plants over the 4yr of sample collection. Moreover, consistent differences in kd and RUP were observed among plants: kd ranged from 0.069 to 0.113/h (OPAA assay) and 0.075 to 0.120/h (OPAF assay), and RUP estimates ranged from 51 to 43% (OPAA assay) and 49 to 41% (OPAF assay). Regression of kd on insoluble N content of CM yielded correlation coefficients (R(2))=0.40 (OPAA assay) and 0.42 (OPAF assay), and regressions of kd on NDIN and N-fraction B3 yielded R(2)<0.02. Mean estimates from both OPAA and OPAF assays for casein, SSBM, ESBM, and CM were, respectively, kd=0.764, 0.161, 0.050, and 0.093/h and RUP=18, 33, 56, and 45%. A range of 8 percentage units from lowest to highest RUP suggests that substantial differences exist in metabolizable protein content of CM produced by different processing plants.

Precision-feeding dairy heifers a high rumen-degradable protein diet with different proportions of dietary fiber and forage-to-concentrate ratios

The objective of this experiment was to determine the effects of feeding a high-rumen-degradable protein (RDP) diet when dietary fiber content is manipulated within differing forage-to-concentrate ratio (F:C) on nutrient utilization of precision-fed dairy heifers. Six cannulated Holstein heifers (486.98±15.07kg of body weight) were randomly assigned to 2 F:C, low- (45% forage; LF) and high-forage (90% forage; HF) diets and to a fiber proportion sequence [33% grass hay and wheat straw (HS), 67% corn silage (CS; low fiber); 50% HS, 50% CS (medium fiber); and 67% HS, 33% CS (high fiber)] within forage proportion administered according to a split-plot, 3×3 Latin square design (16-d periods). Heifers fed LF had greater apparent total-tract organic matter digestibility coefficients (dC), neutral detergent fiber, and cellulose than those fed LC diets. Substituting CS with HS resulted in a linear reduction in dry matter, organic matter, and cellulose dC. Nitrogen dC was not different between F:C or with increasing proportions of HS in diets, but N retention tended to decrease linearly as HS was increased in the diets. Predicted microbial protein flow to the duodenum decreased linearly with HS addition and protozoa numbers HS interacted linearly, exhibiting a decrease as HS increased for LF, whereas no effects were observed for HF. Blood urea N increased linearly as HS was incorporated. The LF-fed heifers had a greater ruminal volatile fatty acids concentration. We noted a tendency for a greater dry matter, and a significantly higher liquid fraction turnover rate for HF diets. There was a linear numerical increase in the liquid and solid fraction turnover rate as fiber was added to the diets. Rumen fermentation parameters and fractional passages (solid and liquid) rates support the reduction in dC, N retention, and microbial protein synthesis observed as more dietary fiber is added to the rations of dairy heifers precision-fed a constant proportion of rumen-degradable protein.

Influence of grinding on the nutritive value of peas for ruminants: comparison between in vitro and in situ approaches

In ruminant nutrition, peas are characterized by high protein solubility and degradability, which impair its protein value estimated by the official in situ method. Grinding can be used as a technological treatment of pea seeds to modify their nutritional value. The aim of this study was to compare the in situ method with an in vitro method on the same pea either in a coarse pea flour form (PCF) or in a ground pea fine flour form (PFF) to understand the effect of grinding. Both forms were also reground (GPCF and GPFF). PCF presented a lower rate of in vitro degradation than PFF, and more stable fermentation parameters (pH, ammonia, soluble carbohydrates) even if gas production was higher for the PCF after 48 h of incubation. In situ dry matter and protein degradation were lower for PCF than those for PFF; these differences were more marked than with the in vitro method. Reground peas were very similar to PFF. The values for pea protein digestible in the intestine (PDI) were higher for PCF than those for PFF. This study points out the high sensitivity of the in situ method to grinding. The study needs to be validated by in vivo measurements.

Compartmental flux andin situmethods underestimate total feed nitrogen as judged by the omasal sampling method due to ignoring soluble feed nitrogen flow

The objective of the present study was to estimate ruminal feed N outflow in lactating cows using the omasal sampling, compartmental flux orin situmethod. A total of five ruminally fistulated Finnish Ayrshire dairy cows were used in a 5 × 5 Latin square study with 21 d periods. Experimental silages of grass or red clover harvested at two stages of maturity in addition to a supplement of 9·0 kg concentrate/d were fed to the cows.In vivoomasal N flow was determined using the omasal sampling technique. Ruminalin situN flow was calculated from N intake and degradability (38 μm nylon bags). The samples of ruminal contents and faeces were divided into seven particle-size fractions by wet sieving; the concentrations of indigestible neutral-detergent fibre and N were used to calculate N flow in the compartmental flux method.In vivoomasal N flow was greater for the red clover silage diets than for the grass silage diets. The N flow calculated using the compartmental flux technique and that calculated using thein situtechnique were highly correlated, but both were less than and poorly correlated with thein vivoN flow. In bothin situand compartmental flux techniques, forage maturity increased the particle-associated N flow, with the increase being significantly greater for the red clover diets than for the grass silage diets. In conclusion, the compartmental flux andin situmethods described the N flow associated with the particle fractions rather than the total ruminal outflow of feed N.

Soluble Non-ammonia Nitrogen in Ruminal and Omasal Digesta of Korean Native Steers Supplemented with Soluble Proteins

An experiment was conducted to study the effect of soluble protein supplements on concentration of soluble non-ammonia nitrogen (SNAN) in the liquid phase of ruminal (RD) and omasal digesta (OD) of Korean native steers, and to investigate diurnal pattern in SNAN concentration in RD and OD. Three ruminally cannulated Korean native steers in a 3×3 Latin square design consumed a basal diet of rice straw and corn-based concentrate (control), and that supplemented (kg/d DM basis) with intact casein (0.24; IC) or acid hydrolyzed casein (0.46; AHC). Ruminal digesta was sampled using a vacuum pump, whereas OD was collected using an omasal sampling system at 2.0 h intervals after a morning feeding. The SNAN fractions (free amino acid (AA), peptide and soluble protein) in RD and OD were assessed using the ninhydrin assay. Concentrations of free AA and total SNAN in RD were significantly (p<0.05) lower than those in OD. Although free AA concentration was relatively high, mean peptide was quantitatively the most important fraction of total SNAN in both RD and OD, indicating that degradation of peptide to AA rather than hydrolysis of soluble protein to peptide or deamination may be the most limiting step in rumen proteolysis of Korean native steers. Diurnal variation in peptide concentration in OD for the soluble protein supplemented diets during the feeding cycle peaked 2 h post-feeding and decreased thereafter whereas that for the control was relatively constant during the entire feeding cycle. Diurnal variation in peptide concentration was rather similar between RD and OD.

Effects of ethnicity and socioeconomic status on survival and severity of fibrosis in liver transplant recipients with hepatitis C virus

The ethnicity and socioeconomic status of the host may affect the progression of hepatitis C virus (HCV). We aimed to compare survival and fibrosis progression in Hispanic white (HW) and non-Hispanic white (NHW) recipients of liver transplantation (LT) with HCV. All HW and NHW patients with HCV who underwent transplantation between January 2000 and December 2007 at 2 centers were retrospectively assessed. The primary outcomes were the time to death, death or graft loss due to HCV, and significant fibrosis [at least stage 2 of 4]. Five hundred eleven patients were studied (159 HW patients and 352 NHW patients), and the baseline demographics were similar for the 2 groups. NHW patients were more likely to be male, to have attended college, and to have private insurance, and they had a higher median household income (MHI). The unadjusted rates of survival (log-rank P = 0.93), death or graft loss due to HCV (P = 0.89), and significant fibrosis (P = 0.95) were similar between groups. In a multivariate analysis controlling for center, age [hazard ratio (HR) per 10 years = 1.43, P = 0.01], donor age (HR per 10 years = 1.25, P < 0.001), and rejection (HR = 1.47, P = 0.048) predicted death, whereas HW ethnicity (HR = 1.06, P = 0.77) was not significant. Independent predictors of significant fibrosis were HW ethnicity (HR = 2.42, P = 0.046), MHI (HR per $10,000 = 1.11, P = 0.01), donor age (HR per 10 years = 1.13, P = 0.02), cold ischemia time (HR = 1.06, P = 0.03), and the interaction between ethnicity and MHI (HR = 0.82, P = 0.03). In conclusion, there is no difference in post-LT survival or graft loss due to HCV between HW patients and NHW patients. Socioeconomic factors may influence disease severity; this is suggested by our findings of more significant fibrosis in HW patients with a low MHI.

Partitioning of nutrient net fluxes across the portal-drained viscera in sheep fed twice daily: effect of dietary protein degradability

Extrusion is used to decrease leguminous seed protein degradability in the rumen in order to shift part of the dietary protein digestion towards the small intestine. The effect of such displacement of digestion site on the partitioning of nutrient net fluxes across the gastrointestinal tract was studied using four sheep fitted with catheters and blood-flow probes, allowing measurements across the rumen, the mesenteric-drained viscera (MDV) and the portal-drained viscera (PDV). Two diets containing 34 % of pea seeds were tested in a crossover design. They differed only according to pea treatment: raw pea (RP) or extruded pea (EP) diet. Rumen undegradable protein (RUP) accounted for 23 and 40 % of dietary crude protein for RP and EP diets, respectively. Across the rumen wall, ammonia net flux was lower with EP diet, whereas urea net flux was not different. Across the MDV, free amino acid (FAA) net flux was greater with EP diet, whereas peptide amino acid net flux was not different, accounting for 7 % of the non-protein amino acid net release. From RP to EP diet, PDV net flux of ammonia decreased by 23 %, whereas FAA net release increased by 21 %. The difference in dietary RUP did not affect the PDV net flux of SCFA, 3-hydroxybutyrate, lactate and glucose. In conclusion, the partial shift in pea protein digestion from the rumen to the small intestine did not affect the portal net balance of N, but decreased N loss from the rumen, and increased amino acid intestinal absorption and portal delivery.

Effect of different protein sources on the concentrations of small peptides in the rumen of sheep

The experiment was conducted to determine the effect of different protein sources on concentration of small peptides (Pro-Ala, Val-Val, Pro-Leu, Met-Met) in the rumen fluid of sheep. Four Inner Mongolia Sunite sheep fitted with permanent cannulas were used in a 4 x 4 Latin square design, and fed four different protein sources including soybean meal (SBM), casein (Casein), fish meal (FM) and corn gluten meal (CGM), respectively. The results showed that the concentration of Pro-Ala peaked in Casein, FM, CGM groups at 2 h after feeding, whereas the highest level was measured at 6 h after feeding in SBM group. Val-Val and Pro-Leu production were highest at 6 h after feeding Casein and CGM diets and 4 h after feeding SBM and FM diets, respectively. During 6 h after feeding the accumulative concentration of Pro-Ala (1.74 mg/l) and Pro-Leu (25.78 mg/l) in rumen was highest for the Casein diet. During the total sampling time, the highest amount of accumulated small peptides was measured for Pro-Leu, and lowest amount for Met-Met, which was independent of treatment groups. Experimental results proved that small peptides with N-terminal Pro and a hydrophobic structure could inhibit rumen degradation and may be available for post-ruminal absorption.

Omasal Flow of Soluble Proteins, Peptides, and Free Amino Acids in Dairy Cows Fed Diets Supplemented with Proteins of Varying Ruminal Degradabilities

Three ruminally and duodenally cannulated cows were assigned to an incomplete 4 x 4 Latin square with four 14-d periods and were fed diets supplemented with urea, solvent soybean meal, xylose-treated soybean meal (XSBM), or corn gluten meal to study the effects of crude protein source on omasal canal flows of soluble AA. Soluble AA in omasal digesta were fractionated by ultrafiltration into soluble proteins greater than 10 kDa (10K), oligopeptides between 3 and 10 kDa (3-10K), peptides smaller than 3 kDa (small peptides), and free AA (FAA). Omasal flow of total soluble AA ranged from 254 to 377 g/d and accounted for 9.2 to 15.9% of total AA flow. Averaged across diets, flows of AA in 10K, 3-10K, small peptides, and FAA were 29, 217, 50, and 5 g/d, respectively, and accounted for 10.3, 71.0, 17.5, and 1.6% of the total soluble AA flow. Cows with diets supplemented with solvent soybean meal had higher flows of Met, Val, and total AA associated with small peptides than those whose diets were supplemented with XSBM, whereas supplementation with corn gluten meal resulted in higher total small peptide-AA flows than did XSBM. Averaged across diets, 27, 75, and 93% of soluble AA in 10K, 3-10K, and peptides plus FAA flowing out of the rumen were of dietary origin. On average, 10% of the total AA flow from the rumen was soluble AA from dietary origin, indicating a substantial escape of dietary soluble N from ruminal degradation. Omasal concentrations and flows of soluble small peptides isolated by ultrafiltration were substantially smaller than most published ruminal small peptide concentrations and outflows measured in acid-deproteinized supernatants of digesta.

Influence of the pattern of peptide supply on microbial activity in the rumen simulating fermenter (RUSITEC)

The source and pattern of N supply was varied in the rumen simulation technique (RUSITEC) in order to determine if continuous, rather than transient, availability of peptides was required for optimum ruminal fermentation. The energy source was fibre prepared from sugar-beet pulp. N was added as NH3continuously infused (AC) or peptides (Bacto®Casitone, a pancreatic hydrolysate of casein; Difco Laboratories, Detroit, MI, USA) continuously infused (PC) or added as a single dose at the time of feeding (PS). Free peptides were detected in the fermenter liquid for 4 h after feeding in the AC treatment, for 10 h in the PS treatment, and at all times with the PC treatment. Treatments had no effect on DM degradation. Approximately 40 % of the degradation occurred during the time no peptides were detected in the PS treatment. Microbial N flow tended to be higher with the peptide additions (P<0·061), with no significant difference between the two peptides treatments. The production of liquid-associated micro-organisms (LAM) was higher in the PC treatment (P<0·05) and the proportion of LAM derived from NH3lower (P<0·05). However, LAM only accounted for 20–30 % total microbial population. Our main conclusion was that peptides had a small stimulatory effect on the fermentation, but there was no indication that synchrony of supply of energy and amino acid-N in the fermenter promoted a more efficient fermentation than non-synchronous supply. This conclusion must be qualified, however, because some N remained in the fibre and may have become available progressively as the fibre was digested by the micro-organisms.

Effects of natural plant extracts on ruminal protein degradation and fermentation profiles in continuous culture

Eight dual-flow continuous culture fermenters were used in four consecutive periods of 10 d to study the effects of six natural plant extracts on ruminal protein degradation and fermentation profiles. Fermenters were fed a diet with a 52:48 forage:concentrate ratio (DM basis). Treatments were no extract (CTR), 15 mg/kg DM of a mixture of equal proportions of all extracts (MIX), and 7.5 mg/kg DM of extracts of garlic (GAR), cinnamon (CIN), yucca (YUC), anise (ANI), oregano (ORE), or pepper (PEP). During the adaptation period (d 1 through 8), samples for ammonia N and VFA concentrations were taken 2 h after feeding. On d 9 and 10, samples for VFA (2 h after feeding), and peptide, AA, and ammonia N concentrations (0, 2, 4, 6, and 8 h after feeding) were also taken. Differences were declared at P < 0.05. During the adaptation period, total VFA and ammonia N concentrations were not affected by treatments. The acetate proportion was higher from d 2 to 6 in CIN, GAR, ANI, and ORE, and the propionate proportion was lower from d 2 to 4 in CIN and GAR, and from d 2 to 5 in ANI and ORE, compared with CTR. However, the proportion of individual VFA (mol/100 mol) was similar in all treatments after d 6, except for valerate in d 9 and 10, which was lower in PEP (2.8 +/- 0.27) compared with CTR (3.5 +/- 0.27). The average peptide N concentration was 31% higher in MIX, and 26% higher in CIN and YUC compared with CTR (6.5 +/- 1.07 mg/100 mL). The average AA N concentration was 17 and 15% higher in GAR and ANI, respectively, compared with CTR (7.2 +/- 0.77 mg/100 mL). The average ammonia N concentration was 31% higher in ANI and 25.5% lower in GAR compared with CTR (5.5 +/- 0.51 mg/100 mL). The accumulation of AA and ammonia N in ANI suggested that peptidolysis and deamination were stimulated. The accumulation of AA N and the decrease in ammonia N in GAR suggests that deamination was inhibited. The accumulation of peptide N and the numerical decrease in AA N in CIN suggest that peptidolysis was inhibited. Results indicate that plant extracts modified ruminal fermentation, but microbes were adapted to some extracts after 6 d of fermentation. Therefore, data from short-term in vitro fermentation studies may lead to erroneous conclusions, and should be interpreted with caution. Careful selection of these additives may allow the manipulation of protein degradation in the rumen.

Effect of Dietary Level of Rumen-Degraded Protein on Production and Nitrogen Metabolism in Lactating Dairy Cows

Twenty-eight (8 with ruminal cannulas) lactating Holstein cows were assigned to 4 x 4 Latin squares and fed diets with different levels of rumen-degraded protein (RDP) to study the effect of RDP on production and N metabolism. Diets contained [dry matter (DM) basis] 37% corn silage, 13% alfalfa silage, and 50% concentrate. The concentrate contained solvent and lignosulfonate-treated soybean meal and urea, and was adjusted to provide RDP at: 13.2, 12.3, 11.7, and 10.6% of DM in diets A to D, respectively. Intake of DM and yield of milk, fat-corrected milk, and fat were not affected by treatments. Dietary RDP had positive linear effects on milk true protein content and microbial non-ammonia N (NAN) flow at the omasal canal, and a quadratic effect on true protein yield, with maximal protein production at 12.3% RDP. However, dietary RDP had a positive linear effect on total N excretion, with urinary N accounting for most of the increase, and a negative linear effect on environmental N efficiency (kg of milk produced per kg of N excreted). Therefore, a compromise between profitability and environmental quality was achieved at a dietary RDP level of 11.7% of DM. Observed microbial NAN flow and RDP supply were higher and RUP flow was lower than those predicted by the NRC (2001) model. The NRC (2001) model overpredicted production responses to RUP compared with the results in this study. Replacing default NRC degradation rates for protein supplements with rates measured in vivo resulted in similar observed and predicted values, suggesting that in situ degradation rates used by the NRC are slower than apparent rates in this study.

Impact of feeding a raw soybean hull-condensed corn steep liquor pellet on induced subacute ruminal acidosis in lactating cows

We used four ruminally cannulated, multiparous Holstein cows (690 kg; 21 kg/d milk) in a 2-period crossover design to determine the impact of feeding a raw soybean hull-corn steep liquor pellet (SHSL) on induced subacute ruminal acidosis (SARA) in lactating cows. Cows were fed control [30% alfalfa hay, 15% corn silage, 34% corn, 9% whole cottonseed, 5% soybean meal (SBM)] or SHSL (20% of diet DM) diets as TMR. SHSL replaced 6.2% alfalfa hay, 3.7% corn silage, 6.6% corn, and 3.3% SBM. Periods were 15 d (10 d adaptation, 2 d for prechallenge measures, and 3 d of SARA challenge). Cows were fed once daily at a common DMI dictated by the cow consuming the least. Cows were fasted 12 h before the first SARA challenge. For each of the three SARA challenges, cows were offered 75% of their daily diet at 0600 h. The remaining 25% of diet DM was replaced by ground corn, which was mixed with the orts that remained 2 h after feeding and placed into the rumen. Ruminal pH declined linearly with time after feeding, and this decrease was greater during the SARA challenges. Ruminal lactate increased linearly with repeated SARA challenges. Concentrations of total ruminal VFA increased linearly after feeding, and increases were greater when cows were challenged. No differences were observed due to SHSL inclusion. The model induced SARA, but partial replacement of alfalfa, corn silage, corn, and SBM by SHSL did not influence responses to SARA challenges.

Response of forage fiber degradation by ruminal microorganisms to branched-chain volatile fatty acids, amino acids, and dipeptides

This study evaluated the effect of branched-chain volatile fatty acids (VFA; isobutyric acid, isovaleric acid), amino acids (valine, leucine), and dipeptides (valine-valine, leucine-leucine) on neutral detergent fiber (NDF) degradation by rumen microorganisms in vitro. The CP (%) and in situ NDF degradation rate (%/h) for alfalfa, bermudagrass, and pangolagrass hays, and napiergrass silage were 17.2 and 7.5, 4.7 and 3.1, 8.3 and 5.3, and 9.6 and 3.4, respectively. In vitro NDF digestibility was the lowest for bermudagrass; alfalfa and napiergrass were the highest. When the incubation contained more ammonia initially, digestibilities increased, but relative differences among forages were unchanged. Adding branched-chain VFA (2 mM) to incubations increased digestibilities more than controls on 15 out of 16 occasions. The effectiveness varied with isoacids and forages used. Amino acid (2 mM) or dipeptide (1 mM) addition consistently increased digestibility over controls. Amino acids further increased digestibility over corresponding isoacids on 14 occasions. Improvement in digestibility over control by leucine appeared to be greater than that by valine. Digestibilities with dipeptides were always greater than those with isoacids, except for one case. Dipeptide addition further increased digestibility significantly over corresponding amino acids on only six occasions, while percent improvement in digestibility numerically by dipeptides occurred in 10 cases. Valine-valine seemed to exert different effect than leucine-leucine, depending on initial ammonia availability. The results indicate that dipeptides could be more effective than isoacids and amino acids in improving NDF digestion. Forages with high CP content or rapid NDF degradation rate appeared to respond to additives to smaller degrees.

Mathematical estimations of hyper-ammonia producing ruminal bacteria and evidence for bacterial antagonism that decreases ruminal ammonia production(1)

Mixed ruminal bacteria (MRB) from cattle fed hay produced ammonia from protein hydrolysate twice as fast as MRB from cattle fed mostly grain, and a mathematical model indicated that cattle fed hay had approximately four-fold more hyper ammonia-producing ruminal bacteria (HAB). HAB had a high maximum velocity of ammonia production (V(max)) and low substrate affinity (high K(m)), but simulations indicated that only large changes in V(max) or K(m) would cause a large deviation in HAB numbers. Some carbohydrate-fermenting ruminal bacteria produced ammonia at a slow rate (CB-LA), but many of the isolates had almost no activity (CB-NA). The model indicated that the ratio of CB-LA to CB-NA had little impact on HAB numbers. Validations based on predicted ratios of HAB, CB-LA and CB-NA over-predicted the specific activity of ammonia production by MRB, but co-culture incubations indicated that washed MRB from cattle fed grain could inhibit HAB. Because autoclaved MRB had virtually no effect on HAB and the incubations were always carried out at pH 7.0, the inhibition was not simply a chemical effect (e.g. low pH).

De novo synthesis of amino acids by the ruminal bacteria Prevotella bryantii B14, Selenomonas ruminantium HD4, and Streptococcus bovis ES1

The influence of peptides and amino acids on ammonia assimilation and de novo synthesis of amino acids by three predominant noncellulolytic species of ruminal bacteria, Prevotella bryantii B14, Selenomonas ruminantium HD4, and Streptococcus bovis ES1, was determined by growing these bacteria in media containing 15NH4Cl and various additions of pancreatic hydrolysates of casein (peptides) or amino acids. The proportion of cell N and amino acids formed de novo decreased as the concentration of peptides increased. At high concentrations of peptides (10 and 30 g/liter), the incorporation of ammonia accounted for less than 0.16 of bacterial amino acid N and less than 0.30 of total N. At 1 g/liter, which is more similar to peptide concentrations found in the rumen, 0.68, 0.87, and 0.46 of bacterial amino acid N and 0.83, 0.89, and 0.64 of total N were derived from ammonia by P. bryantii, S. ruminantium, and S. bovis, respectively. Concentration-dependent responses were also obtained with amino acids. No individual amino acid was exhausted in any incubation medium. For cultures of P. bryantii, peptides were incorporated and stimulated growth more effectively than amino acids, while cultures of the other species showed no preference for peptides or amino acids. Apparent growth yields increased by between 8 and 57%, depending on the species, when 1 g of peptides or amino acids per liter was added to the medium. Proline synthesis was greatly decreased when peptides or amino acids were added to the medium, while glutamate and aspartate were enriched to a greater extent than other amino acids under all conditions. Thus, the proportion of bacterial protein formed de novo in noncellulolytic ruminal bacteria varies according to species and the form and identity of the amino acid and in a concentration-dependent manner.

Evaluation of chemical and physical properties of feeds that affect protein metabolism in the rumen

The goal of the NC-185 Cooperative Regional Research Project is to provide the information needed to improve the nutrition and feeding of dairy cattle, a major factor determining composition of milk and cost of milk yield. Emphasis is placed on understanding how energy and protein nutrition of lactating cows can be manipulated to increase the quantity and improve the profile of AA passing to the small intestine and to improve yield of milk and milk protein. To achieve this goal, one of the major objectives of this project has been to evaluate quantitatively the chemical and physical properties of protein and energy sources that determine AA availability to lactating cows. Reliable measurements of microbial protein synthesis and protein degradation in the rumen are critical in the evaluation process. Therefore, one of the ongoing areas of investigation of this research project has been to determine the most appropriate methods for estimating microbial protein synthesis and dietary protein degradation in the rumen. Other areas have been investigated, using continuous culture fermenters and ruminally and duodenally cannulated cows, including factors that alter microbial metabolism of N in the rumen and subsequently protein supply to the small intestine, such as sources of carbohydrate, protein, and fat and interrelationships of protein and carbohydrate. Findings of the NC-185 Cooperative Regional Research Project Committee and other investigators are summarized in this review.

Protein systems for feeding ruminant livestock: a European assessment

The metabolizable protein system for ruminants, published recently in the United Kingdom (2), was based upon earlier proposals (3, 4). The system includes a number of changes designed to represent the extent of protein degradation in the rumen and the synthesis of microbial protein as variable functions. The system also provides a more rational description of the energy available for microbial growth (fermentable metabolizable energy) by discounting the energy content of dietary lipids and fermentation end products (silages), which are considered to make a relatively insignificant contribution or none to microbial metabolism. The assessment of availability of undegraded dietary protein in the small intestine is revised also, and variable efficiencies of utilization of absorbed AA in relation to the nature of the synthetic process (e.g., meat and milk) are proposed. This paper considers these changes and assesses the adequacy of current laboratory techniques for determining the protein value of feedstuffs for ruminants. A number of conceptual and technical problems are identified, and ways of overcoming them are discussed. We conclude that such systems must be used in practice with guarded enthusiasm and suggest that mechanistic models, which provide a more appropriate representation of the biological processes, be encouraged as the basis of the next generation of feeding systems.

Influence of supplemental protein source and feeding frequency on rumen fermentation and performance in dairy cows

Multiparous Holstein cows in early lactation were fed a basal mixed ration of 47% (DM) alfalfa and timothy silage and 53% barley and corn concentrate twice daily for ad libitum intake at 1630 and 0600 h. Two supplemental protein sources that differed in their resistance to rumen proteolysis were fed at 9% of total DMI in either two meals per day at 1730 and 0700 h or five meals per day at 1730, 2130, 0200, 0700, and 1200 h. The study was a 4 x 4 Latin square design with six blocks of 4 cows in which one block of cows was fitted with rumen cannulas. Intakes of DM, OM, NDF, and CP were not influenced by treatments. However, cows supplemented with five meals a day tended to consume the mixed ration more rapidly after both the p.m. and a.m. feedings. Milk yield and its content of protein, fat, and lactose also were not influenced by treatments. Average rumen pH was higher, and propionate concentrations were lower, for cows supplemented with five meals, but diurnal patterns were not influenced. Propionate and rumen ammonia N concentrations were lower for cows supplemented with the more resistant protein source; however, rumen VFA, as well as soluble and peptide N concentrations, were not influenced by the type of supplemental protein. Results do not support benefits of synchronized rumen release of energy and N to overall cow production, but rather support previous research that soluble protein or peptide N, or both, may act as a pool to provide N for microbial growth at times of the day when ammonia N concentrations are very low.

Effect of monensin on the specific activity of ammonia production by ruminal bacteria and disappearance of amino nitrogen from the rumen

When unadapted mixed ruminal bacteria (312 mg of protein per liter) were treated with monensin (5 mM) in vitro, the rates of ammonia production from enzymatic digests of casein, gelatin, and soy protein (0.5 g of N per liter) were decreased from 46 +/- 2 to 24 +/- 1, 20 +/- 1 to 7 +/- 1, and 40 +/- 2 to 18 +/- 2 nmol/mg of protein per min, respectively. Monensin also caused a decrease in ammonia production in vivo. Nonlactating dairy cows which were fed 0.56 kg of timothy hay 12 times per day had a steady-state ruminal ammonia concentration of 2.7 +/- 0.1 mM, and the ammonia concentration decreased to 1.2 +/- 0.2 mM when monensin (350 mg/day) was added to the diet. The decrease in ammonia production was associated with a 10-fold reduction (4.1 x 10(6) versus 4.2 x 10(5)/ml) in the most probable number of ammonia-producing ruminal bacteria that could use protein hydrolysate as an energy source. Monensin had little effect on the most probable number of carbohydrate-utilizing ruminal bacteria (6.5 versus 7.0 x 10(8)/ml). The addition of protein hydrolysates (560 g) to the rumen caused a rapid increase in the ammonia concentration, but this increase was at least 30% lower when the animals were fed monensin.(ABSTRACT TRUNCATED AT 250 WORDS)

Variations in the uptake and metabolism of peptides and amino acids by mixed ruminal bacteria in vitro

Mixed ruminal bacteria, isolated from sheep (Q and W) fed a concentrate and hay diet, were anaerobically incubated with either 14C-peptides or 14C-amino acids. Experiment 1 showed that uptake of both 14C-labeled substrates was rapid, but the rate for amino acids was twofold greater than for peptides (molecular weight, 1,000 to 200) initially but was similar after 10 min. Experiment 2 demonstrated that metabolism was also rapid; at least 90% of either 14C-labeled substrate was metabolized by 3 min. Of the radioactivity remaining in bacteria, approximately 30% was in the form of 14C-amino acids, but only in leucine, tyrosine, and phenylalanine. Supernatant radioactivity was contained only in tyrosine, phenylalanine, and mostly proline for incubations with 14C-amino acids but in up to 10 amino acids when 14C-peptides were the substrates. Short-term incubations (< 5 min; experiment 3) confirmed previous uptake patterns and showed that the experimental system was responsive to substrate competition. Experiment 4 demonstrated that bacteria from sheep Q possessed initial and maximum rates of 14C-amino acid uptake approximately fourfold greater (P < 0.01) than those of 14C-peptides, but with no significant differences (P > 0.1) between four 14C-peptide substrate groups with molecular weights of 2,000 to < 200. By contrast, bacteria from sheep W showed no such distinctions (P > 0.1) between rates for 14C-peptides and 14C-amino acids. Calculations suggested that peptides could supply from 11 to 35% and amino acids could supply from 36 to 68% of the N requirements of mixed ruminal bacteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutrient requirements versus supply in the dairy cow: strategies to account for variability

Dairy producers must overcome substantial challenges to achieve milk outputs > 14,000 kg of milk/yr per cow within the next decade. To obtain high productivity, a more complete comprehension of the dynamics of metabolism, nutrient utilization, and nutrient absorption will enable better prediction of the efficiency of utilization of these nutrients. A better understanding of the dynamics of rumen function and a more accurate prediction of nutrient flow from the rumen are necessary. Grouping strategy and group feeding behavior influence cow productivity and farm profitability. Understanding of the variance of individual cow responses to management practice is critical. Feeding system design and management and diet formulation techniques need to be developed that recognize the dynamic nature of cow physiology and the variability in feedstuffs and cow requirements. These concepts need to be integrated into total farm management and require the use of new computer modeling technologies.

Recent developments in gastrointestinal absorption and tissue utilization of peptides: a review

Considerable evidence has been accumulated regarding the absorption of dipeptides and tripeptides, yet, even with the growing body of knowledge, the nutritional and metabolic significance of peptide absorption is not fully understood, especially in ruminants. Muscle, mammary gland, liver, kidney, intestinal mucosa, and other tissues either have been shown to have, or are suspected to have, the ability to utilize peptides as a source of AA to meet cellular demands. Investigations suggest that ruminal microbes have the ability to produce substantial amounts of small peptides as a consequence of their hydrolysis of dietary proteins. The extent to which intact peptides may be absorbed into the blood is controversial. Some of the inconsistency in reported observations may be because of limitations of analytical procedures, species differences, or both. Peptide absorption appears to be an important physiological process in ruminants and may constitute the primary source of absorbed AA. The recent observation that the stomach region of the gastrointestinal tract may be an important site of peptide absorption is highly significant. Emerging evidence for the contribution that peptide absorption makes to AA provisioning of ruminants may change some of the currently held views about protein utilization in these unique animals.

Resistance of proline-containing peptides to ruminal degradation in vitro

Mixed ruminal bacteria utilized an enzymatic digest of casein at a rate faster than that for an enzymatic digest of gelatin, but neither amino acid source was completely utilized even when the incubation period was as long as 96 h. Since the reaction of ninhydrin with the residual nonammonia, nonprotein nitrogen was more than twofold stronger when the samples were hydrolyzed with 6 N HCl, it appeared that much of the residual nitrogen was from peptides. Approximately 66% of the nonammonia, nonprotein, ninhydrin-reactive material could not be recovered as amino acids, but there was a significant decrease in total amino acid nitrogen when the samples were pretreated with a C18 Sep-Pak column to remove peptides. The resistant peptides had an abundance of proline, and subsequent incubations showed that synthetic dipeptides which contained proline were hydrolyzed slowly. Lysine appears to be the amino acid which is most apt to limit ruminant production. Dipeptides containing proline and lysine were hydrolyzed at least fivefold slower than lysine-alanine. Methionine, another potentially limiting amino acid, was also degraded at a slower (2.5-fold) rate when it was present as part of a proline dipeptide.

Balancing carbohydrates and proteins for optimum rumen microbial yield

Establishing conditions under which rumen fermentation will be optimized requires an understanding of the nutrient requirements of the mixed microbial population. The major nutrients required by rumen microbes are carbohydrates and proteins, but the most suitable sources and quantities needed to support maximum growth have not been determined. Digestion of proteins results in the production of peptides, which can accumulate in the rumen. Peptides are further hydrolyzed to amino acids, some of which are deaminated, producing ammonia. Although peptides, amino acids, and ammonia all may individually serve as sources of N for various microbes, the total population achieves the highest growth rate on mixtures of all three sources. In a somewhat analogous manner, carbohydrates are digested by exoenzymes to oligosaccharides that are available for crossfeeding by the mixed microbial population. Based on data from both in vitro and in vivo studies, there is general agreement that rate of digestion of carbohydrates is the major factor controlling the energy available for microbial growth; in addition, rate of digestion of total carbohydrate is directly related to proportion of starches, pectins, and sugars. Proteins affect both total fermentation and production of microbial DM per unit of carbohydrate fermented. It appears that the quantity of ruminally available protein needed to optimize microbial growth may, under some conditions, be as high as 14 to 15% of diet DM.