Reducing dietary protein and supplementation with starch or rumen-protected methionine and its effect on performance and nitrogen efficiency in dairy cows fed a red clover and grass silage-based diet

The increasing cost of milk production, in association with tighter manure N application regulations and challenges associated with ammonia emissions in many countries, has increased interest in feeding lower crude protein (CP) diets based on legume silages. Most studies have focused on alfalfa silage, and little information is available on low-CP diets based on red clover silage. Our objectives were to examine the effects of dietary CP content and supplementing a low-CP diet with dietary starch or rumen-protected Met (RPMet) on the performance, metabolism, and nitrogen use efficiency (NUE; milk N output/N intake) in dairy cows fed a red clover and grass silage-based diet. A total of 56 Holstein-Friesian dairy cows were blocked and randomly allocated to 1 of 4 diets over a 14-wk feeding period. Diets were based on red clover and grass silages at a ratio of 50:50 on a dry matter (DM) basis and were fed as a total mixed ration, with a 53:47 ratio of forage to concentrate (DM basis). The diets were formulated to supply a similar metabolizable protein (MP) content, and had a CP concentration of either 175 g/kg DM (control [CON]) or 150 g/kg DM (low-protein [LP]), or LP supplemented with either additional barley as a source of starch (LPSt; +64 g/kg DM) or RPMet (LPM; +0.3 g/100 g MP). At the end of the 14-wk feeding period, 20 cows (5 per treatment) continued to be fed the same diets for a further 6 d, and total urine output and fecal samples were collected. We observed that dietary treatment did not affect DM intake, with a mean of 21.5 kg/d; however, we also observed an interaction between diet and week with intake being highest in cows fed LPSt in wk 4 and CON in wk 9 and 14. Mean milk yield, 4% fat-corrected milk, and energy-corrected milk were not altered by treatment. Similarly, we found no effect of dietary treatment on milk fat, protein, or lactose content. In contrast, milk and plasma urea concentrations were highest in cows fed CON. The concentration of blood plasma β-hydroxybutyrate was highest in cows receiving LPM and lowest in LPSt. Apparent NUE was 28.6% in cows fed CON and was higher in cows fed any of the low-protein diets (LP, LPSt, or LPM), with a mean value of 34.2%. The sum of milk fatty acids with a chain length below C16:0 was also highest in cows fed CON. We observed that dietary treatment did not affect the apparent whole-tract nutrient digestibility of organic matter, N, neutral detergent fiber, and acid detergent fiber, with mean values of 0.785, 0.659, 0.660, and 0.651 kg/kg respectively, but urinary N excretion was approximately 60 g/d lower in cows fed the low-CP diets compared with CON. We conclude that reducing the CP content of red clover and grass silage-based diets from 175 to 150 g/kg DM while maintaining MP supply did not affect performance, but reduced the urinary N excretion and improved NUE, and that supplementing additional starch or RPMet had little further effect.

A meta-analysis of the relationship between milk protein production and absorbed amino acids and digested energy in dairy cattle

Milk protein production is the largest draw on AA supplies for lactating dairy cattle. Prior NRC predictions of milk protein production have been absorbed protein (MP)-based and utilized a first-limiting nutrient concept to integrate the effects of energy and protein, which yielded poor accuracy and precision (root mean squared error (RMSE) > 21%). Using a meta-data set gathered, various alternative equation forms considering MP, absorbed total essential AA (EAA), absorbed individual EAA, and digested energy (DE) supplies as additive drivers of production were evaluated, and all were found to be superior in statistical performance to the first limitation approach (RMSE = 14-15%). Inclusion of DE intake and a quadratic term for MP or absorbed EAA supplies were found to be necessary to achieve intercept estimates (non-productive protein use) that were similar to the factorial estimates of NASEM. The partial linear slope for MP was found to be 0.409, which is consistent with the observed slope bias of -0.34g/g when a slope of 0.67 was used for MP efficiency in a first-limiting nutrient system. Replacement of MP with the supplies of individual absorbed EAA expressed in g/d and a common quadratic across the EAA resulted in unbiased predictions with improved statistical performance as compared with MP-based models. Based on Akaike's Information Criterion (AIC) and biological consistency, the best equations included absorbed His, Ile, Lys, Met, Thr, the non-essential AA, and individual DE intakes from fatty acids, neutral detergent fiber, residual organic matter, and starch. Several also contained a term for absorbed Leu. These equations generally had RMSE of 14.3% and a concordance correlations (CCC) of 0.76. Based on the common quadratic and individual linear terms, milk protein response plateaus were predicted at approximately 320 g/d of absorbed His, Ile, and Lys; 395 g/d of absorbed Thr; 550 g/d of absorbed Met; and 70 g/d of absorbed Leu. Therefore, responses to each except Leu are almost linear throughout the normal in vivo range. De-aggregation of the quadratic term and parsing to individual absorbed EAA resulted in non-biological estimates for several EAA indicating over-parameterization. Expression of the EAA as g/100 g of total absorbed EAA or as ratios of DE intake and using linear and quadratic terms for each EAA resulted in similar statistical performance, but the solutions had identifiability problems and several non-biological parameter estimates. The use of ratios also introduced nonlinearity in the independent variables which violates linear regression assumptions. Further screening of the global model using absorbed EAA expressed as g/d with a common quadratic using an all-models approach, and exhaustive cross-evaluation indicated the parameter estimates for body weight, all 4 DE terms, His, Ile, Lys, Met, and the common quadratic term were stable, while estimates for Leu and Thr were known with less certainty. Use of independent and additive terms and a quadratic expression in the equation results in variable efficiencies of conversion. The additivity also provides partial substitution among the nutrients. Both of these prevent establishment of fixed nutrient requirements in support of milk protein production.

Impacts of red clover and sainfoin silages on the performance, nutrient utilization and milk fatty acids profile of ruminants: A meta-analysis

Inclusion of plants rich in secondary metabolites into grass ensiling offers multiple benefits for ruminants, from improving productive performance to health-promoting effects as well as helping to reduce environment pollution. The present meta-analysis summarizes the dietary inclusion levels of red clover silage (RCS) and sainfoin silages (SS) as well as the types of silages fed to dairy cows and small ruminants. A total of 37 in vivo studies (26 articles in dairy cows and 11 articles in small ruminants) were aggregated after being strictly selected using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A mixed model methodology was used to examine our objectives. This method declares the subject 'study' as random effects and 'inclusion level' as fixed effects. Results indicated that RCS proportion was not associated with nutrient digestibility except for a quadratic effect (p < 0.05) on neutral detergent fibre digestibility. Higher RCS inclusion linearly increased (p < 0.05) nitrogen (N) intake but had no effect on dairy cows' production. Increasing RCS proportion altered milk fatty acid profile where the concentration of conjugated linolenic acid (CLA), C18:3 α-linolenic acid (ALA) and C18:0 linearly increased (p < 0.01). In small ruminants, SS proportion had no relationship with nutrient digestibility, N metabolism and growth performance (p > 0.05). However, a combination of dietary RCS + SS resulted in significantly higher (p < 0.05) CLA and ALA concentration in cow milk and average daily gain (ADG) in small ruminants compared to diets composed from either grass silage or alfalfa silage. Altogether, this meta-analysis highlights the synergistic effects of a combination of SS + RCS inclusion in improving milk fatty acids (FA) profile of dairy cows and ADG of small ruminants.

Effects of forage and grain legume-based silages supplemented with faba bean meal or rapeseed expeller on lactational performance, nitrogen utilization, and plasma amino acids in dairy cows

The objective of this experiment was to investigate the effect of forage type [red clover (51%)-grass silage, i.e., RCG; vs. faba bean (66%)-grass silage, i.e., FBG] and concentrate type (faba bean, FB; vs. rapeseed expeller, RE) on lactational performance, milk composition and nitrogen (N) utilization in lactating dairy cows. Eight lactating multiparous Nordic Red cows were used in a replicated 4 × 4 Latin Square experiment, with 21-d periods, in a 2 × 2 factorial arrangement of treatments. The experimental treatments were as follows: (1) RCG with RE, (2) RCG with FB, (3) FBG with RE, and (4) FBG with FB. Inclusion rates of RE and FB were isonitrogenous. Crude protein contents of the experimental diets were 16.3, 15.9, 18.1, and 17.9% of dry matter, respectively. All diets included oats and barley and were fed ad libitum as total mixed rations with forage-to-concentrate ratio of 55:45. Dry matter intake and milk yield were recorded daily, and spot samples of urine, feces, and blood were collected at the end of each experimental period. Dry matter intake did not differ across diets, averaging 26.7 kg/d. Milk yield averaged 35.6 kg/d and was 1.1 kg/d greater for RCG versus FBG, and milk urea N concentration was lower for RCG compared with FBG. Milk yield was 2.2 kg/d and milk protein yield 66 g/d lower for FB versus RE. Nitrogen intake, urinary N, and urinary urea N excretions were lower, and milk N excretion tended to be lower for RCG compared with FBG. The proportion of the dietary N excreted as fecal N was larger in cows fed RCG than for those fed FBG, and the opposite was true for urinary N. We detected an interaction for milk N as percentage of N intake: it increased with RE compared with FB for RCG-based diet, but only a marginal increase was observed for FBG-based diet. Plasma concentration of His and Lys were lower for RCG than for FBG, whereas His tended to be greater and Lys lower for FB compared with RE. Further, plasma Met concentration was around 26% lower for FB than for RE. Of milk fatty acids, saturated fatty acids were decreased by RCG and increased by FB compared with FBG and RE, respectively, whereas monounsaturated fatty acids were increased by RCG versus FBG, and were lower for FB than for RE. In particular, 18:1n-9 concentration was lower for FB compared with RE. Polyunsaturated fatty acids, such as 18:2n-6 and 18:3n-3, were greater for RCG than for FBG, and 18:2n-6 was greater and 18:3n-3 was lower for FB versus RE. In addition, cis-9,trans-11 conjugated linoleic acid was lower for FB compared with RE. Faba bean whole-crop silage and faba bean meal have potential to be used as a part of dairy cow rations, but further research is needed to improve their N efficiency. Red clover-grass silage from a mixed sward, without inorganic N fertilizer input, combined with RE, resulted in the greatest N efficiency in the conditions of this experiment.

Methane emission, nutrient digestibility, and rumen microbiota in Holstein heifers fed 14 different grass or clover silages as the sole feed

This experiment investigated the variation in enteric methane production and associated gas exchange parameters, nutrient digestibility, rumen fermentation, and rumen microbiome when a range of silages based on different forage types (grass or clover), and different species within the 2 types, were fed as the sole feed to heifers. Three grass species (perennial ryegrass, festulolium, and tall fescue) and 2 clover species (red clover and white clover) were included. Perennial ryegrass was harvested at 2 maturity stages in the primary growth, white clover was harvested once in the primary growth, and 4 cuts of festulolium and tall fescue and 3 cuts of red clover were harvested during the growing season, giving 14 different silage batches in total. Sixteen Holstein heifers 16 to 21 mo old and 2 to 5 mo in pregnancy were fed the silages ad libitum as the sole feed in an incomplete crossover design. Each silage was fed to 4 heifers, except for the 2 perennial ryegrass silages, which were fed to 8 heifers; in total 64 observations. The CH₄ production was measured for 3 d in respiration chambers. Heifers fed clover silages had higher dry matter intake (DMI) compared with heifers fed grass silages, and heifers fed tall fescue silages had the numerically the lowest DMI. Compared with grass silages, feeding clover silages led to higher crude protein digestibility but lower neutral detergent fiber (NDF) digestibility. Rumen pH was higher in heifers fed clover silages compared with those fed grass silages. Based on composition analysis, the rumen microbiota of the heifers clustered clearly according to forage type and species. More specifically, 7 of the 34 dominating rumen bacterial genus-level groups showed higher relative abundances for the clover silages, whereas 7 genus-level groups showed higher abundances for the grass silages. Methane yield was higher for heifers fed grass silages than for those fed clover silages when methane production was related to dry matter and digestible organic matter intake, whereas the opposite was seen when related to NDF digestion. The gross energy lost as methane (CH₄ conversion factor, %) reduced from 7.5% to 6.7%, equivalent to an 11% reduction. The present study gives the outlines for choosing the optimal forage type and forage species with respect to nutrient digestibility and enteric methane emission in ruminants.

Methane emissions and rumen metabolite concentrations in cattle fed two different silages

In this study, 18 animals were fed two forage-based diets: red clover (RC) and grass silage (GS), in a crossover-design experiment in which methane (CH₄) emissions were recorded in respiration chambers. Rumen samples obtained through naso-gastric sampling tubes were analysed by NMR. Methane yield (g/kg DM) was significantly lower from animals fed RC (17.8 ± 3.17) compared to GS (21.2 ± 4.61) p = 0.008. In total 42 metabolites were identified, 6 showing significant differences between diets (acetate, propionate, butyrate, valerate, 3-phenylopropionate, and 2-hydroxyvalerate). Partial least squares discriminant analysis (PLS-DA) was used to assess which metabolites were more important to distinguish between diets and partial least squares (PLS) regressions were used to assess which metabolites were more strongly associated with the variation in CH₄ emissions. Acetate, butyrate and propionate along with dimethylamine were important for the distinction between diets according to the PLS-DA results. PLS regression revealed that diet and dry matter intake are key factors to explain CH₄ variation when included in the model. Additionally, PLS was conducted within diet, revealing that the association between metabolites and CH₄ emissions can be conditioned by diet. These results provide new insights into the methylotrophic methanogenic pathway, confirming that metabolite profiles change according to diet composition, with consequences for CH₄ emissions.

Isoflavones in Animals: Metabolism and Effects in Livestock and Occurrence in Feed

Soybeans are a common ingredient of animal feed. They contain isoflavones, which are known to act as phytoestrogens in animals. Isoflavones were described to have beneficial effects on farm animals. However, there are also reports of negative outcomes after the consumption of isoflavones. This review summarizes the current knowledge of metabolization of isoflavones (including the influence of the microbiome, phase I and phase II metabolism), as well as the distribution of isoflavones and their metabolites in tissues. Furthermore, published studies on effects of isoflavones in livestock species (pigs, poultry, ruminants, fish) are reviewed. Moreover, published studies on occurrence of isoflavones in feed materials and co-occurrence with zearalenone are presented and are supplemented with our own survey data.

Diets for Dairy Cows with Different Proportions of Crude Protein Originating from Red Clover Silage versus Soybean Meal: Ruminal Degradation and Intestinal Digestibility of Amino Acids

The purpose was to assess the effect of exchanging crude protein (CP) of soybean meal (SBM) with red clover silage (RCS) in total mixed rations (TMR) on ruminal degradation and intestinal digestibility (ID) of essential amino acids (EAA). Four TMR and their individual feed components were studied. The TMR were composed of forage and concentrates (75:25), with proportions of RCS in TMR of 0.15, 0.30, 0.45, and 0.60 on a dry matter basis, resulting in diet groups RCS15, RCS30, RCS45, and RCS60, respectively. The ruminal degradation of EAA was determined using the nylon bag technique. For this, samples of TMR and their individual feed components were ruminally incubated for 16 h. The feed residues of TMR obtained after 16 h of incubation were used for the determination of ID of EAA using the mobile-bag technique. Increasing RCS and reducing SBM proportions linearly increased (p < 0.01) the in situ ruminal degradation of individual EAA from 75.5% to 83.5%. The degradation of EAA followed the trend of CP degradation among TMR, except for Cys that was lower (p < 0.05) than that of CP in RCS60 (79.7% vs. 86.3%). The degradation of EAA in individual feed ingredients not always corresponded to the degradation of CP and was feed dependent. Increasing the proportions of RCS in the TMR linearly reduced (p < 0.001) the ID of EAA (except for Ile) from 78.2% to 67.3%. However, the ID of EAA did not always reflect the ID of CP, and in general, the differences between the ID of CP and EAA increased as RCS increased in the TMR. The ID values of most of the EAA were similar (p > 0.05) to ID of CP in RCS15 and RCS30, while they mostly differed (p < 0.05) in RCS45 and RCS60, and being higher for EAA than CP (except for Cys that was lower than CP, p < 0.05). Similar trends were observed for intestinal absorbable AA, resulting in higher values (p < 0.05) of intestinal absorbable for all EAA than of CP in diet RCS60. In conclusion, increasing levels of RCS in TMR reduced the extent of EAA flow into the small intestine, the ID of EAA, and consequently the intestinal absorbable EAA. Therefore, accurate determination of metabolizable AA must be considered for optimal diet formulation when including high proportions of RCS in diets of high-producing dairy cows.

Chopping Roughage Length Improved Rumen Development of Weaned Calves as Revealed by Rumen Fermentation and Bacterial Community

Roughage particle size can influence rumen development, which is also determined by rumen microorganisms and their metabolic end-products. Therefore, the aim of this study was to evaluate the comprehensive effects of roughage length and rumen bacterial community on the rumen development of weaned calves. A total of thirty-six weaned Angus female calves (125 ± 3 d; 161.2 ± 13.0 kg) were randomly assigned to three diets differing in roughage particle size: 4 cm (short length); 24 cm (medium length); and 44 cm (long length). Results showed that chopping roughage increased dry matter intake and organic matter apparent digestibility; altered rumen fermentation indicated by the increased rumen butyrate and valerate concentrations; and increased plasma glucose, cholesterol, and total protein. Chopping roughage affected rumen bacterial community, as indicated by altering the diversity indices; by increasing ruminal bacteria Papillibacter and Eubacterium_hallii_group, which are involved in butyrate production; and by increasing Synergistetes and Mogibacterium, which are involved in bacterial colonization. In conclusion, chopping roughage at 4 cm was shown to improve the rumen bacterial community, alter rumen fermentation, eventually promote the development of rumen.

Microbial diversity and fermentation profile of red clover silage inoculated with reconstituted indigenous and exogenous epiphytic microbiota

The study investigated the effects of transplantation and reconstitution of indigenous and exogenous epiphytic microbiota on the fermentation quality and microbial community of red clover silage. Sterile red clover was inoculated with distilled water (RC0), extracted epiphytic microbiota of red clover (RC), maize (MZ), and sorghum (SG). RC inoculation rapidly decreased pH at the onset of ensiling. The LA concentration and ratio of LA/AA were higher in RC silage during entire ensiling while MZ silage during late phase of ensiling. Pediococcus was dominant in RC early silage, while Lactobacillus was abundant in MZ final silage. The SG terminal silage had higher pH (>4.50) and dominated by Sphingomonas, Enterobacter, and Novosphingobium. RC and MZ microbiota were beneficial in enhancing fermentation quality and microbial community in red clover silage. Transplantation and reconstitution of epiphytic microbiota can be a successful method to assess the effective and eco-friendly additive for the targeted crop.

Impact of Bovine Diet on Metabolomic Profile of Skim Milk and Whey Protein Ingredients

The influence of bovine diet on the metabolome of reconstituted skim milk powder (SMP) and protein ingredients produced from the milk of cows fed on pasture or concentrate-based diets was investigated. Cows were randomly assigned to diets consisting of perennial ryegrass only (GRS), perennial ryegrass/white clover sward (CLV), or indoor total mixed ration (TMR) for an entire lactation. Raw milk obtained from each group was processed at pilot scale, to produce SMP and sweet whey, and SMP was further processed at laboratory scale, to yield ideal whey and acid whey. The total amino acid composition and metabolome of each sample were analyzed, using high-performance cation exchange and a targeted combination of direct-injection mass spectrometry and reverse-phase liquid chromatography–tandem mass spectrometry (LC–MS/MS), respectively. The nitrogen composition of the products from each of the diets was similar, with one exception being the significantly higher nonprotein nitrogen content in TMR-derived skim milk powder than that from the GRS system. Total amino acid analysis showed significantly higher concentrations of glycine in GRS- and CLV-derived sweet whey and acid whey than in those from TMR. The cysteine contents of CLV-derived ideal whey and acid whey were significantly higher than for TMR, while the valine content of GRS-derived acid whey was significantly higher than TMR. The phenylalanine content of GRS-derived ideal whey was significantly higher than that from CLV. Metabolomic analysis showed significantly higher concentrations of the metabolites glutamine, valine, and phosphocreatine in each ingredient type derived from TMR than those from GRS or CLV, while the serine content of each GRS-derived ingredient type was significantly higher than that in TMR-derived ingredients. These results demonstrate that the type of bovine feeding system used can have a significant effect on the amino acid composition and metabolome of skim milk and whey powders and may aid in the selection of raw materials for product manufacture, while the clear separation between the samples gives further evidence for distinguishing milk products produced from different feeding systems based on LC–MS/MS.

In Vitro Evaluation of Different Dietary Methane Mitigation Strategies

We assessed and ranked different dietary strategies for mitigating methane (CH4) emissions and other fermentation parameters, using an automated gas system in two in vitro experiments. In experiment 1, a wide range of dietary CH4 mitigation strategies was tested. In experiment 2, the two most promising CH4 inhibitory compounds from experiment 1 were tested in a dose-response study. In experiment 1, the chemical compounds 2-nitroethanol, nitrate, propynoic acid, p-coumaric acid, bromoform, and Asparagopsis taxiformis (AT) decreased predicted in vivo CH4 production (1.30, 21.3, 13.9, 24.2, 2.00, and 0.20 mL/g DM, respectively) compared with the control diet (38.7 mL/g DM). The 2-nitroethanol and AT treatments had lower molar proportions of acetate and higher molar proportions of propionate and butyrate compared with the control diet. In experiment 2, predicted in vivo CH4 production decreased curvilinearly, molar proportions of acetate decreased, and propionate and butyrate proportions increased curvilinearly with increased levels of AT and 2-nitroethanol. Thus 2-nitroethanol and AT were the most efficient strategies to reduce CH4 emissions in vitro, and AT inclusion additionally showed a strong dose-dependent CH4 mitigating effect, with the least impact on rumen fermentation parameters.

Predictions of ruminal outflow of essential amino acids in dairy cattle

The objective of this work was to update and evaluate predictions of essential AA (EAA) outflows from the rumen. The model was constructed based on previously derived equations for rumen-undegradable (RUP), microbial (MiCP), and endogenous (EndCP) protein outflows from the rumen, and revised estimates of ingredient composition and EAA composition of the protein fractions. Corrections were adopted to account for incomplete recovery of EAA during 24-h acid hydrolysis. The predicted ruminal protein and EAA outflows were evaluated against a data set of observed values from the literature. Initial evaluations indicated a minor mean bias for non-ammonia, non-microbial nitrogen flow ([RUP + EndCP]/6.25) of 16 g of N per day. Root mean squared errors (RMSE) of EAA predictions ranged from 26.8 to 40.6% of observed mean values. Concordance correlation coefficients (CCC) of EAA predictions ranged from 0.34 to 0.55. Except for Leu, all ruminal EAA outflows were overpredicted by 3.0 to 32 g/d. In addition, small but significant slope biases were present for Arg [2.2% mean squared error (MSE)] and Lys (3.2% MSE). The overpredictions may suggest that the mean recovery of AA from acid hydrolysis across laboratories was less than estimates encompassed in the recovery factors. To test this hypothesis, several regression approaches were undertaken to identify potential causes of the bias. These included regressions of (1) residual errors for predicted EAA flows on each of the 3 protein-driven EA flows, (2) observed EAA flows on each protein-driven EAA flow, including an intercept, (3) observed EAA flows on the protein-driven EAA flows, excluding an intercept term, and (4) observed EAA flows on RUP and MiCP. However, these equations were deemed unsatisfactory for bias adjustment, as they generated biologically unfeasible predictions for some entities. Future work should focus on identifying the cause of the observed prediction bias.

Metabolisable energy of grass and red clover silages fed to sheep at maintenance level

This study investigated the effect of forage type (grass or red clover) and harvesting time (primary growth or regrowth) of silage on energy and N utilisation by sheep fed at maintenance level. Specifically, the assumption of constant loss of energy of digestible organic matter from energy losses in urine and CH4 applied in evaluation of silage metabolisable energy (ME) was investigated. Urinary excretion of high-energy phenolic compounds related to solubilisation of lignin was assumed to affect urinary energy (UE) losses from sheep fed highly digestible grass silage (GS). A total of 25 primary growth and regrowth silages of timothy (Phleum pratense) and meadow fescue (Festuca pratensis) grass mixtures and red clover (Trifolium pratense) samples collected in digestibility trials with sheep, including faecal and urine samples, were used for energy and N determinations. Urinary concentration of monophenolic compounds and CH4 emissions in vitro were also analysed. Daily faecal N output, CH4 yield (MJ/kg DM intake), proportion of CH4 energy in digestible energy (DE) and proportion of UE in DE were greater (P ≤ 0.03) in sheep fed red clover silage (RCS) than GS. Furthermore, less (P = 0.01) energy was lost as UE of DE in sheep fed primary growth GS compared with the other treatments. The relationship between UE and silage N intake or urinary N output for both silage types (i.e. grass v. red clover) was strong, but the fit of the regressions was better for GS than RCS. The CH4/DE ratio decreased (P < 0.05) and the UE/DE ratio increased (P < 0.05) with increasing organic matter digestibility in RCS. These relationships were not significant (P < 0.05) for the GS diets. The regression coefficient was higher (P < 0.05) for GS than RCS when regressing ME concentration on digestible organic matter. The results of this study imply that ME/DE ratio is not constant across first-cut GS of different maturities. The ME production response may be smaller from highly digestible first-cut GS but could not be clearly related to urinary excretion of monophenols derived from solubilisation of lignin. Furthermore, energy lost in urine was not clearly defined for RCS and was much more predictable for GS from silage N concentration.

Nitrogen and fatty acid rumen metabolism in cattle offered high or low polyphenol oxidase red clover silage

Polyphenol oxidase (PPO) in red clover (RC) has been shown to reduce both lipolysis and proteolysis in silo and implicated (in vitro) in the rumen. However, all in vivo comparisons have compared RC with other forages, typically with lower levels of PPO, which brings in other confounding factors as to the cause for the greater protection of dietary nitrogen (N) and C18 polyunsaturated fatty acids (PUFA) on RC silage. This study compared two RC silages which when ensiled had contrasting PPO activities (RC+ and RC-) against a control of perennial ryegrass silage (PRG) to ascertain the effect of PPO activity on dietary N digestibility and PUFA biohydrogenation. Two studies were performed the first to investigate rumen and duodenal flow with six Hereford×Friesian steers, prepared with rumen and duodenal cannulae, and the second investigating whole tract N balance using six Holstein-Friesian non-lactating dairy cows. All diets were offered at a restricted level based on animal live weight with each experiment consisting of two 3×3 Latin squares using big bale silages ensiled in 2010 and 2011, respectively. For the first experiment digesta flow at the duodenum was estimated using a dual-phase marker system with ytterbium acetate and chromium ethylenediaminetetraacetic acid as particulate and liquid phase markers, respectively. Total N intake was higher on the RC silages in both experiments and higher on RC- than RC+. Rumen ammonia-N reflected intake with ammonia-N per unit of N intake lower on RC+ than RC-. Microbial N duodenal flow was comparable across all silage diets with non-microbial N higher on RC than the PRG with no difference between RC+ and RC-, even when reported on a N intake basis. C18 PUFA biohydrogenation was lower on RC silage diets than PRG but with no difference between RC+ and RC-. The N balance trial showed a greater retention of N on RC+ over RC-; however, this response is likely related to the difference in N intake over any PPO driven protection. The lack of difference between RC silages, despite contrasting levels of PPO, may reflect a similar level of protein-bound-phenol complexing determined in each RC silage. Previously this complexing has been associated with PPOs protection mechanism; however, this study has shown that protection is not related to total PPO activity.

Replacing maize silage plus soybean meal with red clover silage plus wheat in diets for lactating dairy cows

The objectives of this study were to evaluate the effects of replacing maize silage plus soybean meal with red clover silage (RCS) plus wheat on feed intake, diet digestibility, N partitioning, urinary excretion of purine derivatives, and milk production in dairy cows. Forty-four lactating German Holstein cows were used in a 4 × 4 Latin square design with 21-d periods composed of a 13-d adaptation phase followed by an 8-d sampling phase. Experimental diets offered as total mixed ration consisted of a constant forage-to-concentrate ratio (75:25) with targeted proportions of RCS-to-maize silage of 15:60 (RCS15), 30:45 (RCS30), 45:30 (RCS45), and 60:15 (RCS60) on a dry matter (DM) basis. Increasing the proportion of RCS plus wheat in the diet decreased linearly the intake of DM from 22.4 to 19.8 kg/d, and of organic matter from 21.1 to 18.1 kg/d. The apparent total tract digestibility (ATTD) of DM and organic matter did not differ across diets and averaged 68.4 and 70.5%, respectively. However, ATTD of N decreased linearly from 68.5 to 63.2%, whereas ATTD of neutral detergent fiber and acid detergent fiber increased linearly from 50.4 to 59.6% and from 48.4 to 57.7%, respectively, when increasing the proportion of RCS plus wheat. Fecal N excretion increased from 31.6 (RCS15) to 37.2% (RCS60) of N intake, whereas urinary N excretion was the lowest (32.8% of N intake) with RCS45. Hence, N efficiency (milk N/N intake) decreased linearly with incremental levels of RCS plus wheat, being the lowest when feeding RCS60 (25.4%), probably due to increased nonprotein N proportion in total dietary N. Urinary excretion of purine derivatives decreased linearly from 378 to 339 mmol/d, which suggests that increasing levels of RCS plus wheat reduced the microbial crude protein flow at the duodenum. Milk yield and milk protein concentration declined linearly from 35.9 to 30.2 kg/d and from 3.20 to 3.01%, respectively, when increasing the proportion of RCS plus wheat. In conclusion, caution should be taken before introducing high levels of RCS plus wheat in diets of high-yielding dairy cows. However, RCS plus wheat can be included up to 30% of the dairy cow diet (DM basis) without a reduction in lactation performance.

Effects of replacement of late-harvested grass silage and barley with early-harvested silage on ruminal digestion efficiency in lactating dairy cows

The objective of this experiment was to quantify the effects of graded replacement of late-harvested grass silage and barley with early-harvested silage on nutrient digestion and rumen fermentation. Four experimental diets were fed to 4 multiparous rumen-cannulated Nordic Red cows in 4 × 4 Latin square design with 21-d periods. Dietary treatments consisted of late-cut grass silage (LS) and rolled barley, which was gradually replaced with early-cut grass silage [ES; 0, 33, 67, and 100% of the forage component (ES + LS) of the diet]. With increased proportion of ES in the diet, the proportion of barley decreased from 47.2 to 26.6% on a dry matter basis. Early- and late-cut silages were harvested at 2-wk intervals (predicted concentrations of metabolizable energy 11.0 and 9.7 MJ/kg of dry matter). The 4 diets were formulated to support the same milk production. Nutrient flows were quantified using omasal sampling technique applying the triple-marker method (Cr, Yb, and indigestible neutral detergent fiber) and ¹⁵N as a microbial marker. Feed intake decreased with graded replacement of LS and barley with ES, but milk production was not influenced by diet. Digestibility of nutrients improved with graded addition of ES in the diet with the greatest difference observed in digestibility of neutral detergent fiber (NDF) and potentially digestible NDF (pdNDF). The results suggested that improved cell wall digestibility with graded level of ES in the diet was partly related to higher intrinsic digestibility of ES than LS, and partly due to negative associative effects with an increased proportion of LS and barley in the diet. Efficiency of microbial N synthesis was not influenced by the diet, but ruminal protein degradability increased with ES in the diet. Rumen fermentation pattern was not affected by the diet despite large difference in the profile of dietary carbohydrates. Rumen pool size of NDF and pdNDF, and ruminal turnover time of NDF decreased with graded addition of ES in the diet, whereas digestion rate of pdNDF improved. The results of this study indicate that increased CH₄ yield in a parallel production study with graded addition of ES in the diet were more related to greater ruminal and total digestibility of organic matter than to the changes in rumen fermentation pattern.

Predicting omasal flow of nonammonia N and milk protein yield from in vitro-determined utilizable crude protein at the duodenum

This study evaluated the relationship between utilizable crude protein (uCP) at the duodenum estimated in vitro and omasal flow of crude protein (CP; omasal flow of nonammonia N × 6.25) measured in lactating dairy cows. In vivo data were obtained from previous studies estimating omasal digesta flow using a triple-marker method and ¹⁵N as microbial marker. A total of 34 different diets based on grass and red clover silages were incubated with buffered rumen fluid previously preincubated with carbohydrates for 3 h. The buffer solution was modified to contain 38 g of NaHCO₃ and 1 g of (NH₄)HCO₃ in 1,000 mL of distilled water. Continuous sampling of the liquid phase for determination of ammonia-N was performed at 0.5, 4, 8, 12, 24, and 30 h after the start of incubation. The ammonia N concentrations after incubation were used to calculate uCP. The natural logarithm of uCP [g/kg of dry matter (DM)] at time points 0.5, 4, 8, 12, 24, and 30 h of incubation was plotted against time to estimate the concentration of uCP (g/kg of DM) at time points 16, 20, and 24 h using an exponential function. Fixed model regression analysis and mixed model regression analysis with random study effect were used to evaluate the relationships between predicted uCP (supply and concentration) and observed omasal CP flow and milk protein yield. Residual analysis was also conducted to evaluate whether any dietary factors influenced the relationships. The in vitro uCP method ranked the diets accurately in terms of total omasal CP flow (kg/d) or omasal CP flow per kilogram of DM intake. We also noted a close relationship between estimated uCP supply and adjusted omasal CP flow, as demonstrated by a coefficient of determination of 0.87, although the slope of 0.77 indicated that estimated uCP supply (kg/d) was greater than the value determined in vivo. The linear bias with mixed model analysis indicated that uCP supply overestimated the difference in omasal CP flow between the diets within a study, an error most likely related to study differences in feed intake, animals, and methodology. Predicting milk protein yield from uCP supply showed a positive relationship using a mixed model (coefficient of determination = 0.79), and we observed no difference in model fit between the time points of incubation (16, 20, or 24 h). The results of this study indicate that the in vitro method can be a useful tool in evaluating protein value of ruminant diets.

Substituting oat hay or maize silage for portion of alfalfa hay affects growth performance, ruminal fermentation, and nutrient digestibility of weaned calves

OBJECTIVE

The impact of forage feeding strategy on growth performance, ruminal fermentation and nutrient digestibility in post-weaning calves was investigated.

METHODS

Forty-five female Holstein calves (body weight [BW] = 79.79±0.38 kg) were enrolled in the 35-d study at one week after weaning and randomly assigned to one of three dietary treatments. All diets were fed as total mixed ration containing 60% (dry matter [DM] basis) of basal starter feed and 40% (DM basis) of forage, but varied in composition of forage source including i) alfalfa (40% DM, AH); ii) alfalfa hay (26.7% DM)+oat hay (13.3% DM; OH); iii) alfalfa hay (26.7% DM)+corn silage (13.3% DM; WS).

RESULTS

Dry matter intake was not different among treatment groups (p>0.05). However, BW (p<0.05) and average daily gain (p<0.05) of calves fed AH and OH were greater than WS-fed calves, whereas heart girth was greater in OH-fed calves than those fed AH and WS (p<0.05). Ruminal fermentation parameters including proportion of butyric acid, acetated-to-propionate ratio, concentration of total volatile fatty acid, protozoal protein, bacterial protein, and microbial protein in rumen were the highest in OH (p<0.05) and the lowest in WS. Compared with the AH and WS, feeding oat hay to postweaning calves increased crude protein digestibility (p<0.05), and decreased duration of diarrhea (p<0.05) and fecal index (p<0.05).

CONCLUSION

Our results suggested that partially replacing alfalfa hay with oat hay improved ruminal fermentation, nitrogen utilization, and reduced incidence of diarrhea in post-weaning dairy calves.

Feed intake and milk production in dairy cows fed different grass and legume species: a meta-analysis

The aim of this meta-analysis was to compare feed intake, milk production, milk composition and organic matter (OM) digestibility in dairy cows fed different grass and legume species. Data from the literature was collected and different data sets were made to compare families (grasses v. legumes, Data set 1), different legume species and grass family (Data set 2), and different grass and legume species (Data set 3+4). The first three data sets included diets where single species or family were fed as the sole forage, whereas the approach in the last data set differed by taking the proportion of single species in the forage part into account allowing diets consisting of both grasses and legumes to be included. The grass species included were perennial ryegrass, annual ryegrass, orchardgrass, timothy, meadow fescue, tall fescue and festulolium, and the legume species included were white clover, red clover, lucerne and birdsfoot trefoil. Overall, dry matter intake (DMI) and milk production were 1.3 and 1.6 kg/day higher, respectively, whereas milk protein and milk fat concentration were 0.5 and 1.4 g/kg lower, respectively, for legume-based diets compared with grass-based diets. When comparing individual legume species with grasses, only red clover resulted in a lower milk protein concentration than grasses. Cows fed white clover and birdsfoot trefoil yielded more milk than cows fed red clover and lucerne, probably caused by a higher OM digestibility of white clover and activity of condensed tannins in birdsfoot trefoil. None of the included grass species differed in DMI, milk production, milk composition or OM digestibility, indicating that different grass species have the same value for milk production, if OM digestibility is comparable. However, the comparison of different grass species relied on few observations, indicating that knowledge regarding feed intake and milk production potential of different grass species is scarce in the literature. In conclusion, different species within family similar in OM digestibility resulted in comparable DMI and milk production, but legumes increased both DMI and milk yield compared with grasses.

Effect of incremental amounts of camelina oil on milk fatty acid composition in lactating cows fed diets based on a mixture of grass and red clover silage and concentrates containing camelina expeller

Camelina is an ancient oilseed crop that produces an oil rich in cis-9,cis-12 18:2 (linoleic acid, LA) and cis-9,cis-12,cis-15 18:3 (α-linolenic acid, ALA); however, reports on the use of camelina oil (CO) for ruminants are limited. The present study investigated the effects of incremental CO supplementation on animal performance, milk fatty acid (FA) composition, and milk sensory quality. Eight Finnish Ayrshire cows (91d in milk) were used in replicated 4×4 Latin squares with 21-d periods. Treatments comprised 4 concentrates (12kg/d on an air-dry basis) based on cereals and camelina expeller containing 0 (control), 2, 4, or 6% CO on an air-dry basis. Cows were offered a mixture of grass and red clover silage (RCS; 1:1 on a dry matter basis) ad libitum. Incremental CO supplementation linearly decreased silage and total dry matter intake, and linearly increased LA, ALA, and total FA intake. Treatments had no effect on whole-tract apparent organic matter or fiber digestibility and did not have a major influence on rumen fermentation. Supplements of CO quadratically decreased daily milk and lactose yields and linearly decreased milk protein yield and milk taste panel score from 4.2 to 3.6 [on a scale of 1 (poor) to 5 (excellent)], without altering milk fat yield. Inclusion of CO linearly decreased the proportions of saturated FA synthesized de novo (4:0 to 16:0), without altering milk fat 18:0, cis-9 18:1, LA, and ALA concentrations. Milk fat 18:0 was low (<5g/100g of FA) across all treatments. Increases in CO linearly decreased the proportions of total saturates from 58 to 45g/100g of FA and linearly enriched trans-11 18:1, cis-9,trans-11 18:2, and trans-11,cis-15 18:2 from 5.2, 2.6, and 1.7 to 11, 4.3, and 5.8g/100g of FA, respectively. Furthermore, CO quadratically decreased milk fat trans-10 18:1 and linearly decreased trans-10,cis-12 18:2 concentration. Overall, milk FA composition on all treatments suggested that one or more components in camelina seeds may inhibit the complete reduction of 18-carbon unsaturates in the rumen. In conclusion, CO decreased the secretion of saturated FA in milk and increased those of the trans-11 biohydrogenation pathway or their desaturation products. Despite increasing the intake of 18-carbon unsaturated FA, CO had no effect on the secretions of 18:0, cis-9 18:1, LA, or ALA in milk. Concentrates containing camelina expeller and 2% CO could be used for the commercial production of low-saturated milk from grass- and RCS-based diets without major adverse effects on animal performance.

Assessment of dietary ratios of red clover and corn silages on milk production and milk quality in dairy cows

Twenty-four multiparous Holstein-Friesian dairy cows were used in a replicated 3×3 Latin square changeover design experiment to test the effects of changing from corn (Zea mays) silage to red clover (Trifolium pratense) silage in graded proportions on feed intakes, milk production, and whole-body N and P partitioning. Three dietary treatments with ad libitum access to 1 of 3 forage mixtures plus a standard allowance of 4kg/d dairy concentrates were offered. The 3 treatment forage mixtures were, on a dry matter (DM) basis: (1) R10: 90% corn silage and 10% red clover silage, (2) R50: 50% corn silage and 50% red clover silage, and (3) R90: 10% corn silage and 90% red clover silage. In each of 3 experimental periods, there were 21d for adaptation to diets, and 7d for measurements. Diet crude protein intakes increased, and starch intakes decreased, as the silage mixture changed from 90% corn to 90% red clover, although the highest forage DM intakes and milk yields were achieved on diet R50. Although milk fat yields were unaffected by diet, milk protein yields were highest with the R 0250 diet. Whole-body partitioning of N was measured in a subset of cows (n=9), and both the daily amount and proportion of N consumed that was excreted in feces and urine increased as the proportion of red clover silage in the diet increased. However, the apparent efficiency of utilization of feed N for milk protein production decreased from 0.33g/g for diet R10 to 0.25g/g for diet R90. The urinary excretion of purine derivatives (sum of allantoin and uric acid) tended to increase, suggesting greater flow of microbial protein from the rumen, as the proportion of red clover silage in the diet increased, and urinary creatinine excretion was affected by diet. Fecal shedding of E. coli was not affected by dietary treatment. In conclusion, even though microbial protein flow may have been greatest from the R 0450 diet, optimum feed intakes and milk yields were achieved on a diet that contained a 1:1 DM mixture of corn and red clover silages.

Short communication: Evaluation of nitrogen excretion equations from cattle

Nitrogen excretion in dairy manure is a precursor for N2O and NH3 formation in livestock housing, manure storage facilities, and after manure is applied to land. Nitrous oxide is a major contributor to greenhouse gas emissions, and reducing N output from dairy production facilities can reduce the amount of anthropogenic N2O entering the atmosphere. The objective of the study was to conduct a comprehensive evaluation of extant prediction models for N excretion in feces and urine using extensive literature data. A total of 45 N excretion equations were evaluated for lactating cows, heifers, and nonlactating cows and steers. These equations were evaluated with 215 treatment means from 69 published studies collected over 20 yr from 1995 to 2015. Two evaluation methods were used: the root mean square prediction error and the concordance correlation coefficient. Equations constructed using a more rigorous development process fared better than older extant equations. Equations for heifers and nonlactating cows had greater error of prediction compared with equations used for lactating cows. This could be due to limited amount of data available for construction and evaluation of the equations. Urinary N equations had greater prediction errors than other forms of excretion, possibly due to high variability in urinary N excretion and challenges in urine collection. Fecal N equations had low error bias and reached an acceptable level of precision and accuracy.

Dairy cow responses to graded levels of rapeseed and soya bean expeller supplementation on a red clover/grass silage-based diet

The effects of rapeseed and soya bean expeller (SBE) supplementation on digestion and milk production responses in dairy cows were investigated in an incomplete Latin square design using five cows and four 3-week periods. The experimental diets consisted of five concentrate treatments fed at a rate of 9 kg/day: a mixture of barley and oats, which was replaced with rapeseed or SBE at two levels (CP concentration (g/kg dry matter (DM)) of 130 for the control concentrate and 180 and 230 for the two protein supplemented levels). A mixture of grass and red clover silage (1:1) was fed ad libitum and it had a CP concentration of 157 g/kg DM. Supply of nutrients to the lower tract was measured using the omasal canal sampling technique, and total digestion from total faecal collection. Protein supplementation increased omasal canal amino acid (AA) flows and plasma concentrations of AA, and was also reflected as increased milk production. However, N use efficiency (NUE) decreased with increased protein supplementation. Rapeseed expeller (RSE) tended to increase silage DM intake and elicited higher milk production responses compared with SBE and also resulted in a higher NUE. The differences between the protein supplements in nitrogen metabolism were relatively small, for example, there were no differences in the efficiency of microbial protein synthesis or omasal canal flows of nitrogenous components between them, but plasma methionine concentration was lower for soya bean-fed cows at the high CP level in particular. The lower milk protein production responses to SBE than to RSE supplementation were at least partly caused by increased silage DM and by the lower methionine supply, which may further have been amplified by the use of red clover in the basal diet. Although feed intake, diet digestion, AA supply and milk production were all consistently improved by protein supplementation, there was a simultaneous decrease in NUE. In the current study, the milk protein production increased only 9% and energy-corrected milk production by 7% when high level of protein supplementation (on average 2.9 kg DM/day) was compared with the control diet without protein supplementation showing that dairy production could be sustained at a high level even without external protein supplements, at least in the short term. The economic and environmental aspects need to be carefully evaluated when decisions about protein supplementation for dairy cows are taken.

The effect of high polyphenol oxidase grass silage on metabolism of polyunsaturated fatty acids and nitrogen across the rumen of beef steers

Polyphenol oxidase (PPO) activity in red clover (Trifolium pratense) has been reported to reduce both proteolysis and lipolysis, resulting in greater N use efficiency and protection of PUFA across the rumen. Although high levels of PPO have been reported in grasses such as cocksfoot (orchard grass; Dactylis glomerata), no in vivo research has determined whether grass PPO elicits the same response as red clover PPO. To test the hypothesis that silage ensiled from grass with high levels of PPO protects N and PUFA across the rumen, 6 steers with ruminal and duodenal cannulas were offered cocksfoot silage (CO; high-PPO grass), perennial ryegrass silage (PR; Lolium perenne; low-PPO grass), or red clover silage (RC; high-PPO control) at 16 g DM/kg BW daily with the experiment consisting of two 3 × 3 Latin squares with 21-d periods, consisting of 12 d of diet adaptation, 6 d of duodenal marker infusion, 2 d of duodenal sampling, and 1 d of ruminal sampling. All silages were well preserved, with DM of 34.4, 55.3, and 45.4% for CO, PR, and RC. Activity of PPO in silages was low due to deactivation but was greater in CO than either PR or RC (0.15 vs. 0.05 and 0.08 μkatal/g DM). Protein-bound phenol (mg/g DM) as a measure of the degree of oxidation and an indication of PPO protection was greatest for RC (15.9) but comparable for PR (10.1) and CO (12.2). Biohydrogenation of C18 PUFA was significantly lower on RC compared to the 2 grass silages with CO greater than PR. Despite lower levels of total fatty acid intake and subsequent duodenal flow, CO resulted in greater levels of phytanic acid and total branched and odd chain fatty acids in duodenal digesta than RC or PR. Ruminal ammonia concentration was greatest for RC, with no difference between the grasses. Duodenal flow of microbial N and efficiency of microbial protein synthesis were lowest for CO and comparable for RC and PR. The CO (high-grass PPO) did not result in elevated levels of C18 PUFA escaping the rumen or improve efficiency of total N transfer through the rumen compared to PR. The RC resulted in a greater flow of N and nonmicrobial N to the duodenum than the 2 grasses with PR greater than CO.

Evaluation of between-cow variation in milk urea and rumen ammonia nitrogen concentrations and the association with nitrogen utilization and diet digestibility in lactating cows

Concentrations of milk urea N (MUN) are influenced by dietary crude protein concentration and intake and could therefore be used as a biomarker of the efficiency of N utilization for milk production (milk N/N intake; MNE) in lactating cows. In the present investigation, data from milk-production trials (production data set; n=1,804 cow/period observations from 21 change-over studies) and metabolic studies involving measurements of nutrient flow at the omasum in lactating cows (flow data set; n=450 cow/period observations from 29 studies) were used to evaluate the influence of between-cow variation on the relationship of MUN with MNE, urinary N (UN) output, and diet digestibility. All measurements were made on cows fed diets based on grass silage supplemented with a range of protein supplements. Data were analyzed by mixed-model regression analysis with diet within experiment and period within experiment as random effects, allowing the effect of diet and period to be excluded. Between-cow coefficient of variation in MUN concentration and MNE was 0.13 and 0.07 in the production data set and 0.11 and 0.08 in the flow data set, respectively. Based on residual variance, the best model for predicting MNE developed from the production data set was MNE (g/kg)=238 + 7.0 × milk yield (MY; kg/d) - 0.064 × MY(2) - 2.7 × MUN (mg/dL) - 0.10 body weight (kg). For the flow data set, including both MUN and rumen ammonia N concentration with MY in the model accounted for more variation in MNE than when either term was used with MY alone. The best model for predicting UN excretion developed from the production data set (n=443) was UN (g/d)=-29 + 4.3 × dry matter intake (kg/d) + 4.3 × MUN + 0.14 × body weight. Between-cow variation had a smaller influence on the association of MUN with MNE and UN output than published estimates of these relationships based on treatment means, in which differences in MUN generally arise from variation in dietary crude protein concentration. For the flow data set, between-cow variation in MUN and rumen ammonia N concentrations was positively associated with total-tract organic matter digestibility. In conclusion, evaluation of phenotypic variation in MUN indicated that between-cow variation in MUN had a smaller effect on MNE compared with published responses of MUN to dietary crude protein concentration, suggesting that a closer control over diet composition relative to requirements has greater potential to improve MNE and lower UN on farm than genetic selection.

Methane production, nutrient digestion, ruminal fermentation, N balance, and milk production of cows fed timothy silage- or alfalfa silage-based diets

The objective of this study was to investigate the effects of changing forage source in dairy cow diets from timothy silage (TS) to alfalfa silage (AS) on enteric CH₄ emissions, ruminal fermentation characteristics, digestion, milk production, and N balance. Nine ruminally cannulated lactating cows were used in a replicated 3 × 3 Latin square design (32-d period) and fed (ad libitum) a total mixed ration (TMR; forage:concentrate ratio of 60:40, dry matter basis), with the forage portion consisting of either TS (0% AS; 0% AS and 54.4% TS in the TMR), a 50:50 mixture of both silages (50% AS; 27.2% AS and 27.2% TS in the TMR), or AS (100% AS; 54.4% AS and 0% TS in the TMR). Compared with TS, AS contained less (36.9 vs. 52.1%) neutral detergent fiber but more (20.5 vs. 13.6%) crude protein (CP). In sacco 24-h ruminal degradability of organic matter (OM) was higher for AS than for TS (73.5 vs. 66.9%). Replacement of TS with AS in the diet entailed increasing proportions of corn grain and bypass protein supplement at the expense of soybean meal. As the dietary proportion of AS increased, CP and starch concentrations increased, whereas fiber content declined in the TMR. Dry matter intake increased linearly with increasing AS proportions in the diet. Apparent total-tract digestibility of OM and gross energy remained unaffected, whereas CP digestibility increased linearly and that of fiber decreased linearly with increasing inclusion of AS in the diet. The acetate-to-propionate ratio was not affected, whereas ruminal concentration of ammonia (NH₃) and molar proportion of branched-chain VFA increased as the proportion of AS in the diet increased. Daily CH₄ emissions tended to increase (476, 483, and 491 g/d for cows fed 0% AS, 50% AS, and 100% AS, respectively) linearly as cows were fed increasing proportions of AS. Methane production adjusted for dry matter intake (average=19.8 g/kg) or gross energy intake (average=5.83%) was not affected by increasing AS inclusion in the diet. When expressed on a fat-corrected milk or energy-corrected milk yield basis, CH₄ production increased linearly with increasing AS dietary proportion. Urinary N excretion (g/d) increased linearly when cows were fed increasing amounts of AS in the diet, suggesting a potential for higher nitrous oxide (N₂O) and NH₃ emissions. Efficiency of dietary N use for milk protein secretion (g of milk N/g of N intake) declined with the inclusion of AS in the diet. Despite marked differences in chemical composition and ruminal degradability, under the conditions of this study, replacing TS with AS in dairy cow diets was not effective in reducing CH₄ energy losses.

Effects of forage sources on rumen fermentation characteristics, performance, and microbial protein synthesis in midlactation cows

Eight multiparous Holstein cows (632±12 kg BW; 135±16 DIM) were used in a replicated 4×4 Latin square design to evaluate the effects of forage sources on rumen fermentation characteristics, performance, and microbial protein (MCP) synthesis. The forage portion of the diets contained alfalfa hay (AH), oat hay (OH), Leymus chinensis (LC), or rice straw (RS) as the primary source of fiber. Diets were isonitrogenous and isocaloric, and cows were fed four corn silages based total mixed rations with equivalent nonfiber carbohydrate (NFC) and forage neutral detergent fiber (NDF). Dry matter intake was not affected by the source of dietary forages, ranging from 18.83 to 19.20 kg/d, consequently, milk yield was similar among diets. Because of the numerical differences in milk fat and milk protein concentrations, 4% FCM and ECM yields were unchanged (p>0.05). Mean rumen pH, NH₃-N content, and concentrations of volatile fatty acids in the rumen fluid were not affected by the treatments (p>0.05). Dietary treatments did not affect the total tract apparent digestibility of dry matter, organic matter, and crude protein (p>0.05); however, digestibility of NDF and acid detergent fiber in RS diet was higher compared with AH, OH, and LC diets (p<0.05). Total purine derivative excretion was higher in cows fed AH, OH, and LC diets compared with those fed RS diet (p<0.05), consequently, estimated MCP synthesis was 124.35 g/d higher in cows fed AH diet compared with those fed RS diet (p<0.05). The results indicated that cows fed AH, OH, LC, and RS diets with an equivalent forage NDF and NFC have no unfavourable effect on the ruminal fermentation and productive parameters.

Effect of replacing grass silage with red clover silage on nutrient digestion, nitrogen metabolism, and milk fat composition in lactating cows fed diets containing a 60:40 forage-to-concentrate ratio

Diets based on red clover silage (RCS) typically increase the concentration of polyunsaturated fatty acids (PUFA) in ruminant meat and milk and lower the efficiency of N utilization compared with grass silages (GS). Four multiparous Finnish Ayrshire cows (108 d postpartum) fitted with rumen cannulas were used in a 4 × 4 Latin square design with 21-d periods to evaluate the effect of incremental replacement of GS with RCS on milk production, nutrient digestion, whole-body N metabolism, and milk fatty acid composition. Treatments comprised total mixed rations offered ad libitum, containing 600 g of forage/kg of diet dry matter (DM), with RCS replacing GS in ratios of 0:100, 33:67, 67:33, and 100:0 on a DM basis. Intake of DM and milk yield tended to be higher when RCS and GS were offered as a mixture than when fed alone. Forage species had no influence on the concentration or secretion of total milk fat, whereas replacing GS with RCS tended to decrease milk protein concentration and yield. Substitution of GS with RCS decreased linearly whole-tract apparent organic matter, fiber, and N digestion. Forage species had no effect on total nonammonia N at the omasum, whereas the flow of most AA at the omasum was higher for diets based on a mixture of forages. Replacing GS with RCS progressively lowered protein degradation in the rumen, increased linearly ruminal escape of dietary protein, and decreased linearly microbial protein synthesis. Incremental inclusion of RCS in the diet tended to lower whole-body N balance, increased linearly the proportion of dietary N excreted in feces and urine, and decreased linearly the utilization of dietary N for milk protein synthesis. Furthermore, replacing GS with RCS decreased linearly milk fat 4:0 to 8:0, 14:0, and 16:0 concentrations and increased linearly 18:2n-6 and 18:3n-3 concentrations, in the absence of changes in cis-9 18:1, cis-9, trans-11 18:2, or total trans fatty acid concentration. Inclusion of RCS in the diet progressively increased the apparent transfer of 18-carbon PUFA from the diet into milk, but had no effect on the amount of 18:2n-6 or 18:3n-3 at the omasum recovered in milk. In conclusion, forage species modified ruminal N metabolism, the flow of AA at the omasum, and whole-body N partitioning. A lower efficiency of N utilization for milk protein synthesis with RCS relative to GS was associated with decreased availability of AA for absorption, with some evidence of an imbalance in the supply of AA relative to requirements. Higher enrichment of PUFA in milk for diets based on RCS was related to an increased supply for absorption, with no indication that forage species substantially altered PUFA bioavailability.

Forage polyphenol oxidase and ruminant livestock nutrition

Polyphenol oxidase (PPO) is predominately associated with the detrimental effect of browning fruit and vegetables, however, interest within PPO containing forage crops (crops to be fed to animals) has grown since the browning reaction was associated with reduced nitrogen (N) losses in silo and the rumen. The reduction in protein breakdown in silo of red clover (high PPO forage) increased the quality of protein, improving N-use efficiency [feed N into product N (e.g., Milk): NUE] when fed to ruminants. A further benefit of red clover silage feeding is a significant reduction in lipolysis (cleaving of glycerol-based lipid) in silo and an increase in the deposition of beneficial C18 polyunsaturated fatty acid (PUFA) in animal products, which has also been linked to PPO activity. PPOs protection of plant protein and glycerol based-PUFA in silo is related to the deactivation of plant proteases and lipases. This deactivation occurs through PPO catalyzing the conversion of diphenols to quinones which bind with cellular nucleophiles such as protein reforming a protein-bound phenol (PBP). If the protein is an enzyme (e.g., protease or lipase) the complexing denatures the enzyme. However, PPO is inactive in the anaerobic rumen and therefore any subsequent protection of plant protein and glycerol based-PUFA in the rumen must be as a result of events that occurred to the forage pre-ingestion. Reduced activity of plant proteases and lipases would have little effect on NUE and glycerol based-PUFA in the rumen due to the greater concentration of rumen microbial proteases and lipases. The mechanism for PPOs protection of plant protein in the rumen is a consequence of complexing plant protein, rather than protease deactivation per se. These complexed proteins reduce protein digestibility in the rumen and subsequently increase undegraded dietary protein flow to the small intestine. The mechanism for protecting glycerol-based PUFA has yet to be fully elucidated but may be associated with entrapment within PBP reducing access to microbial lipases or differences in rumen digestion kinetics of the forage and therefore not related to PPO activity.

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.

Efficacy of various naturally occurring caffeic acid derivatives in preventing post-harvest protein losses in forages

BACKGROUND

In red clover, oxidation of endogenous o-diphenols by polyphenol oxidase (PPO) inhibits post-harvest proteolyis. This system is transferable to alfalfa by providing PPO (via a transgene) and o-diphenol PPO substrates (via exogenous application). To exploit the PPO system for protein protection, it would be advantageous to produce PPO substrates in alfalfa, which lacks them. We assessed the extent of PPO-mediated proteolytic inhibition by phenolic compounds, especially those whose biosynthesis could be engineered into alfalfa.

RESULTS

Tested compounds included o-diphenols (caffeic acid, phaselic acid, chlorogenic acid, clovamide) and monophenols (p-coumaric acid, p-coumaroyl-malic acid). In the presence of PPO, 2 mmol o-diphenol g⁻¹ protein reduced 24 h proteolysis 68-87% (P < 0.001) and as little as 0.25 mmol g⁻¹ protein still decreased 24 h proteolysis 43-60% (P < 0.001). At high concentrations, clovamide inhibited 24 h proteolysis 50% (P < 0.001) in the absence of PPO, likely due to non-PPO oxidation. Monophenol p-coumaric acid did not inhibit 24 h proteolyis, although high levels of its malate ester did exhibit PPO- and oxygen-independent inhibition (37%, P < 0.001).

CONCLUSIONS

For PPO-mediated proteolytic inhibition, pathways for both phaselic acid and chlorogenic acid may be good targets for engineering into alfalfa. Clovamide may be useful for inhibiting proteolysis without PPO.