Determination of reticulo-rumen and whole-stomach digestion in lactating cows by omasal canal or duodenal sampling

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 used 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 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 (nonproductive protein use) that were similar to the factorial estimates of the National Academies of Sciences, Engineering, and Medicine (2021). The partial linear slope for MP was found to be 0.409, which is consistent with the observed slope bias of -0.34 g/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 grams per day 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 and biological consistency, the best equations included absorbed His, Ile, Lys, Met, Thr, the NEAA, and individual DE intakes from fatty acids, NDF, residual OM, and starch. Several also contained a term for absorbed Leu. These equations generally had RMSE of 14.3% and a concordance correlation 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 nonbiological estimates for several EAA indicating over-parameterization. Expression of the EAA as g/100 g 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 nonbiological 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 grams per day with a common quadratic using an all-models approach, and exhaustive cross-evaluation indicated the parameter estimates for BW, all 4 DE terms, His, Ile, Lys, Met, and the common quadratic term were stable, whereas 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.

Carbohydrates and protein digestive traits in beef cattle grazing fertilised or mixed tropical pasture

This study was performed to investigate the nitrogen (N) and carbohydrate digestive traits of grazing heifers. The experiment was carried out at the Federal University of Lavras. The treatments were a Marandu palisadegrass (Urochloa brizantha [Syn, Brachiaria brizantha] Stapf. A. Rich. cv. Marandu) monoculture fertilised with 150 kg N/[ha ∙ year] (FP) or Marandu palisadegrass mixed pasture with forage peanut (MP). The pastures were grazed by six rumen-cannulated zebu heifers. A double cross-over design was used in four periods. Nutritive value, intake and apparent digestibility of forage, ruminal traits and kinetics and N balance were evaluated. Apparent total-tract digestibility of dry matter (DM) and neutral detergent fibre (NDF) were greater for FP than for MP. There was no effect in apparent total-tract digestibility of N. The estimated intestinal digestibility of nutrients was greater on MP than FP. Even though N intake and faecal N output were greater on MP than FP, there was no effect in urine N output. The N balance tended to be greater on MP than FP. The forage peanut, which contains condensed tannins, decreased ruminal fibre degradation, apparent digestibility and ruminal protein degradation, increased N flow from the rumen. Inclusion of forage peanut in the mixed pasture decreased the ruminal fibre degradability but increased N retention by the animals.

Ability of three dairy feed evaluation systems to predict postruminal outflows of nitrogenous compounds in dairy cows: A meta-analysis

Adequate prediction of postruminal outflow of protein fractions is the starting point for the determination of metabolizable protein supply in dairy cows. The objective of this meta-analysis was to compare the performance of 3 dairy feed evaluation systems (National Research Council [NRC], Cornell Net Protein and Carbohydrate System [CNCPS], and National Academies of Sciences, Engineering and Medicine [NASEM]) to predict outflows (g/d) of nonammonia nitrogren (NAN), microbial N (MiN), and nonammonia nonmicrobial N (NANMN). Predictions of rumen degradabilities (% of nutrient) of protein (RDP), NDF, and starch were also evaluated. The data set included 1,294 treatment means from 312 digesta flow studies. The 3 feed evaluation systems were compared using the concordance correlation coefficient (CCC), the ratio of root mean square prediction error (RMSPE) on standard deviation of observed values (RSR), and the slope between observed and predicted values. Mean and linear biases were deemed biologically relevant and are discussed if higher than a threshold of 5% of the mean of observed values. The comparisons were done on observed values adjusted or not for the study effect; the adjustment had a small effect on the mean bias but the linear bias reflected a response to a dietary change rather than absolute predictions. For the absolute predictions of NAN and MiN, CNCPS had the best-fit statistics (8% greater CCC; 6% lower RMSPE) without any bias; NRC and NASEM underpredicted NAN and MiN, and NASEM had an additional linear bias indicating that the underprediction of MiN increased at increased predictions. For NANMN, fit statistics were similar among the 3 feed evaluation systems with no mean bias; however, the linear bias with NRC and CNCPS indicated underprediction at low predictions and overprediction at elevated predictions. On average, the CCC were smaller and RSR ratios were greater for MiN versus NAN indicating increased prediction errors for MiN. For NAN responses to a dietary change, CNCPS also had the best predictions, although the mean bias with NASEM was not biologically relevant and the 3 feed evaluation systems did not present a linear bias. However, CNCPS, but not the 2 other feed evaluation systems, presented a linear bias for MiN, with responses being overpredicted at increased predictions. For NANMN, responses were overpredicted at increased predictions for the 3 feed evaluation systems, but to a lesser extent with NASEM. The site of sampling had an effect on the mean bias of MiN and NANMN in the 3 feed evaluation systems. The mean bias of MiN was higher in omasal than duodenal studies in the 3 feed evaluation systems (from 55 to 61 g/d) and this mean bias was twice as large when 15N labeling was used as a microbial marker compared with purines. Such a difference was not observed for duodenal studies. The reasons underlying these systematic differences are not clear as the type of measurements used in the current meta-analysis does not allow to delineate if one site or one microbial marker is yielding the "true" postruminal N outflows. Rumen degradabilities of protein was underpredicted with CNCPS, and RDP responses to a dietary change was underpredicted by the 3 feed evaluation systems with increased RDP predictions. Rumen degradability of NDF was underpredicted and had poor fit statistics for NASEM compared with CNCPS. Fit statistics were similar between CNCPS and NASEM for rumen degradability of starch, but with an underprediction of the response with NASEM and absolute values being overpredicted with CNCPS. Multivariate regression analyses showed that diet characteristics were correlated with prediction errors of N outflows in each feed evaluation system. Globally, compared with NAN and NANMN, residuals of MiN were correlated with several moderators in the 3 feed evaluation systems reflecting the complexity to measure and model this outflow. In addition, residuals of NANMN were correlated positively with RDP suggesting an overestimation of this parameter. In conclusion, although progress is still to be made to improve equations predicting postruminal N outflows, the current feed evaluation systems provide sufficient precision and accuracy to predict postruminal outflows of N fractions.

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.

Effects of faba bean, blue lupin and rapeseed meal supplementation on amino acid metabolism of dairy cows fed grass silage-based diets

Information about the amino acid (AA) supply of locally produced protein supplements to dairy cow metabolism is needed to design sustainable diets for milk production. In this dairy cow experiment, grass silage and cereal-based diets supplemented with isonitrogenous amounts of rapeseed meal (RSM), faba beans (FB) and blue lupin seeds (BL) were compared with a control diet (CON) without protein supplementation. The diets were arranged as a 4 × 4 Latin Square using periods of 21 days, and four rumen-cannulated Nordic Red dairy cows were used in the experiment. The intake of all AAs increased in response to protein supplementation and was for many individual AAs higher when RSM rather than the grain legumes FB and BL were fed. The total AA flow at the omasal canal was 3 026, 3 371, 3 373 and 3 045 g/day for cows fed CON, RSM, FB and BL, respectively, but only RSM resulted in higher milk protein output. This may be explained by the higher provision of essential AA for milk protein synthesis when RSM was fed. The cows fed FB showed some positive features such as a tendency for greater omasal flow of branched-chain AA compared with BL. Overall, low plasma methionine and/or glucose concentrations in all treatments suggest that their supply was possibly limiting further production responses under the dietary conditions of the current study. It seems that the benefits of grain legume supplementation are limited when high-quality grass silage and cereal-based diets are used as the basal diet, but higher responses in amino acid supply and subsequent production responses can be expected when RSM is used.

Effect of inclusion of distillers grains with solubles and crude glycerin in beef cattle finishing diets on ruminal fermentation and fatty acid biohydrogenation

An experiment was conducted to evaluate the impact of feeding bio-fuel co-products on ruminal fermentation characteristics and composition of omasal digesta flow. Four ruminally cannulated Holstein steers (371 ± 5 kg) were used in a 4 × 4 Latin Square design. Omasal sample collection and triple marker technique was used to quantify fatty acid omasal flow. Treatments were applied as a 2 × 2 factorial where a steam flaked corn (SFC) basal diet (DGS-N CG-N) was replaced with 40% of diet DM as corn distillers grains (DGS; DGS-Y CG-N) or 10% of diet DM as crude glycerin (DGS-N CG-Y) or 40% of diet DM distillers grains and 10% of diet DM as crude glycerin (DGS-Y CG-Y). No effects were observed for the interaction of DGS and glycerin on measured rumen characteristics. Dietary inclusion of glycerin decreased (P = 0.05) ruminal content 4-h post feeding on a DM basis but did not influence DMI (P = 0.64). Feeding DGS had no effect (P = 0.34) on particulate passage to the omasum (kg/d) in spite of greater (P = 0.04) DMI. Feeding DGS reduced flow rate (% of rumen volume/h) (P = 0.05) but did not affect total VFA concentration (P = 0.46) or average ruminal pH (P = 0.72). No differences (P > 0.05) were observed in ruminal parameters when feeding glycerin, besides ruminal particulate content (kg) on DM basis (P = 0.05). An interaction of DGS and glycerin affected intake of stearic (P < 0.01), linoleic (P < 0.01), and linolenic acid (P < 0.01). An interaction of DGS and glycerin did not affect individual fatty acid flow with respect to intake for stearic (P = 0.17), linoleic (P = 0.18), or linolenic acid (P = 0.66). Dietary inclusion of glycerin had no impact on g of linolenic (P = 0.16) or linoleic (P = 0.32) acid transformed. A trend was identified for cattle fed diets with glycerin to have increased (P = 0.07) grams of conjugated linoleic acid (CLA; C18:2 cis-9, trans-11) per gram of linoleic acid intake, with no impact on the percent of saturated fat (P = 0.44) or unsaturated fat (P = 0.43) in omasal flow. For cattle fed diets with DGS, fewer grams of linoleic (P < 0.01) and linolenic (P < 0.01) were present in digesta flow per gram of intake. Inclusion of DGS in the treatment diets also increased (P < 0.01) stearic acid flow (g) and CLA flow (g) per gram of stearic and linoleic acid intake, respectively. Observed differences in CLA proportion post fermentation may indicate interrupted biohydrogenation when glycerin is fed.

Evaluating the effects of fibrolytic enzymes on rumen fermentation, omasal nutrient flow, and production performance in dairy cows during early lactation

This study was performed to evaluate the effects of pre-treating a barley-silage-based diet with an exogenous fibrolytic enzyme derived from Trichoderma reesei (FETR, a mixture of xylanase and cellulase) on lactation performance, omasal nutrient flow and digestibility, rumen fermentation characteristics, and rumen pH profile in Holstein dairy cows during early lactation. The dairy trial was conducted using nine Holstein dairy cows (averaging 46 ± 24 days in milk and 697 ± 69 kg body weight, six cows were fitted with a rumen cannula, and three were non-cannulated). Two groups of cows were randomly assigned to each of the dietary treatments in a crossover design: control (without FETR supplementation) and supplemented [with 0.75 mL of FETR·kg−1 dry matter (DM) of the diet based on our previous study]. The application of FETR tended to decrease the DM intake compared with control. There were no effects of FETR (P > 0. 10) on omasal nutrient flow and digestibility, rumen fermentation characteristics, and rumen pH profile. In conclusion, this study lacks evidence that the fibrolytic enzyme (at a level of 0.75 mL of FETR·kg−1 DM) can affect nutrient digestibility, ruminal fermentation, and the performance of early-lactation cows. Further study with larger animal trials are needed.

Omasal flow of nonstructural carbohydrates and nitrogenous compounds in lactating dairy cows fed diets containing timothy cut in the afternoon or morning

Shifting the cutting of grass from morning to afternoon has been shown to increase the concentration of nonstructural carbohydrates (NSC) in forages. We compared the effects of diets (66:34, forage:concentrate ratio) containing a mix (% of the diet dry matter) of baleages (46.5%) and silages (19.3%) harvested from timothy cut in the afternoon (p.m.-cut TIM diet) or morning (a.m.-cut TIM diet) on omasal flows of NSC and nitrogenous fractions, ruminal and total-tract digestibilities of nutrients, plasma concentration of AA, and milk yield and composition. Eight ruminally cannulated Holstein cows averaging (mean ± standard deviation) 31.4 ± 6.13 kg/d of milk, 136 ± 17.0 d in milk, and 611 ± 66.4 kg of body weight in the beginning of the experiment were used in a crossover design with 21-d periods (14 d for diet adaptation and 7 d for data and sample collection). Intake of total ethanol-soluble carbohydrates (TESC; +150 g/d), starch (+129 g/d), and total NSC (TESC plus starch = +278 g/d) was greater with feeding the p.m.- than the a.m.-cut TIM diet. Likewise, the apparent ruminal digestibilities of TESC (+149 g/d), starch (+167 g/d), and total NSC (+316 g/d) increased in the p.m.-cut TIM diet. Diets, however, had no effect on the omasal flows and apparent ruminal and total-tract digestibilities of dry matter and organic matter. Intake of N increased in cows fed the p.m.- versus the a.m.-cut TIM diet (562 and 528 g/d, respectively) despite no effect of diets on dry matter intake. Diets did not affect the omasal flows of total nonammonia N, total bacterial nonammonia N, nonammonia and nonbacterial N, and individual AA, and the efficiency of microbial protein synthesis in the rumen. Contrarily, supply of rumen-degradable protein increased (+9.2%) in cows fed the p.m.-cut TIM diet, with this response driven by the 6.4% increase in N intake. Plasma concentrations of essential and nonessential AA followed the omasal flow of AA and were not changed by diets. Feeding the p.m.- versus the a.m.-cut diet significantly increased yields of 4% fat-corrected milk and milk fat, and tended to increase energy-corrected milk, milk true protein, and milk lactose yields. Overall, feeding the p.m.-cut TIM diet to mid-lactation dairy cows did not improve microbial protein synthesis and omasal flow of AA, and these responses were in line with the lack of a treatment effect on dry matter intake.

Effect of Rye Grain Derived from Different Cultivars or Maize Grain Use in the Diet on Ruminal Fermentation Parameters and Nutrient Digestibility in Sheep

Six wether sheep with ruminal and duodenal cannulas were used in a replicated 3 × 3 Latin square to determine the effect of rye grain (from an open-pollinated or a hybrid cultivar) and maize grain from hybrid cultivar inclusion in the diet on ruminal fermentation parameters and nutrient digestion in different gastrointestinal tract compartments. The experimental diets consisted of meadow hay (800 g/day) and a concentrate mixture (300 g/day) that contained rye grain from an openpollinated cultivar (OPRG), rye grain from a hybrid cultivar (HRG), or maize grain from a hybrid cultivar (MG) as a main energy source. Each experimental period lasted 17 days and consisted of 10 days for diet adaptation and 7 days for data and sample collection. Ruminal fermentation (pH, short-chain fatty acids, and ammonia concentration) and nutrient digestion up to the duodenum (in reticulorumen, omasum, and abomasum), in the intestine, as well as in the total digestive tract was investigated. Mean ruminal pH was higher for MG compared to HRG and OPRG (P<0.01) but did not differ between HRG and OPRG (6.45, 6.35, and 6.29 for MG, HRG, and OPRG, respectively). Treatment did not affect short-chain fatty acid concentration in the rumen, except for the molar proportions of valeric acid and of isovaleric acid of the total short-chain fatty acids, which was or tended to be higher (P≤0.06) for MG compared to HRG and OPRG. Less starch was digested in the gastrointestinal tract up to the duodenum and more in the intestine for MG compared to HRG and OPRG (P=0.01); however, total tract nutrient digestibility did not differ between treatments. In conclusion, usage of rye grain in sheep diets resulted in a lower ruminal pH compared to maize grain usage. No differences for ruminal fermentation, nutrient digestion up to the duodenum, in the intestine, as well as in the total digestive tract between rye grain from open-pollinated and hybrid cultivar usage in sheep diets were found.

Effects of lactic acid bacteria in a silage inoculant on ruminal nutrient digestibility, nitrogen metabolism, and lactation performance of high-producing dairy cows

Silage treated with lactic acid bacteria inoculants has been reported to increase ruminal microbial biomass when tested in vitro. Therefore, we tested if alfalfa silage inoculated with Lactobacillus plantarum MTD-1 would improve ruminal N metabolism and increase milk production in high-producing dairy cows. Twenty-eight early lactation Holstein cows (8 ruminally cannulated) were blocked by DIM and milk production; animals were used in a double crossover design consisting of four 28-d periods. Animals in each block were randomly assigned to 2 treatments: a diet containing uninoculated alfalfa silage (control) and a diet containing alfalfa silage inoculated with L. plantarum MTD-1 (LP). Diets were formulated to contain 50% of alfalfa silage, 16% crude protein, and 25% neutral detergent fiber (dry matter basis). Milk production and dry matter intake were recorded in the last 14 d of each period. Milk samples were collected twice at both daily milkings on d 20, 21, 27, and 28 of each period. On d 22, omasal samples were collected from the cannulated animals over a period of 3 d to quantify ruminal digestibility and nutrient flows. Data were analyzed using mixed models of SAS 9.4 (SAS Institute). Compared to the control, cows receiving the LP treatment had greater milk production (40.4 vs. 39.6 kg/d) and lower milk urea nitrogen concentration (11.6 vs. 12.7 mg/dL), despite minor changes in energy-corrected milk. Milk lactose concentration was greater in the milk produced by cows fed the LP treatment, which reflected a tendency for increased milk lactose yield. Although milk true protein concentration was lower for cows in the LP treatment, milk true protein yield was the same on both control and LP treatments. Improvements in milk production of animals under the LP treatment were associated with greater organic matter truly digested in the rumen, especially ruminal neutral detergent fiber digestion. Minor changes were observed in total omasal microbial nonammonia N flow in cows receiving the LP treatment. Therefore, alfalfa silage treated with L. plantarum MTD-1 may improve ruminal fermentation and milk production; however, because of a lack of response in ruminal N metabolism, these changes did not result in greater energy-corrected milk in high-producing dairy cows.

Predicting ruminally undegraded and microbial protein flows from the rumen

The objectives of the present work were (1) to identify the cause of the linear bias in predictions of rumen-undegradable protein (RUP) content of feeds, and devise methods to remove the bias from prediction equations, and (2) to further explore the impact of rumen-degradable protein (RDP) on microbial N (MiN) outflow from the rumen. The kinetic model used by NRC (2001), which is based on protein fractionation and rates of degradation (Kd) and passage (Kp), displays considerable slope bias (-0.30 kg/kg), indicating parameter or structural problems. Regressing Kp by feed class and a static adjustment factor for the in situ-derived Kd on observed RUP flows completely resolved the slope bias problem, and the model performed significantly better than models using unadjusted Kd and marker-based Kp. The Kd adjustment was 3.82%/h, which represents approximately a 50% increase in rates of degradation over the in situ values, indicating that in situ analyses severely underestimate true rates of protein degradation. The Kp for concentrate-derived protein was 5.83%/h, which was slightly less than the marker-predicted rate of 6.69%/h. However, the derived forage protein rate was 0.49%/h, which was considerably less than the marker-based rate of 5.07%/h. Compartmental analysis of data from a single study corroborated the regression analysis, indicating that a 25% reduction in the overall passage rate and an 87% increase in the rate of degradation were required to align ruminal N pool sizes and the extent of protein degradation with the observed data. Therefore, one must conclude that both the in situ-derived degradation rates and the marker-based particle passage rates are biased relative to protein passage and cannot be used directly to predict RUP outflow from the rumen. The effects of RDP supply on microbial nitrogen (MiN) flow were apparent when intakes of individual nutrients were offered but not when DM intake and individual nutrient concentrations were offered, due to collinearity problems. Microbial N flow from the rumen was found to be linearly related to ruminally degraded starch, ruminally degraded neutral detergent fiber (NDF), RDP, and forage NDF intakes; and quadratically related to residual OM intake. More complicated models containing 2- and 3-way interactions among nutrients were also supported by the data. Independent MiN responses to RDP, ruminally degraded starch, and ruminally degraded NDF aligned with the expected responses to each of those nutrients. Nonlinear representations of MiN were found to be inferior to the linear models. Despite using unbiased predictions of RUP and MiN as drivers of AA flows, predictions of Arg, His, Ile, and Lys flow exhibited linear slope bias relative to the observed data, indicating that representations of the AA composition of the proteins may be biased or the observed data are biased. This is an improvement over the NRC (2001) predictions, where bias adjustments were required for all of the essential AA. Despite the bias for 4 AA flows, the revised prediction system was a substantial improvement over the prior work.

Estimation of ruminal outflow in buffaloes fed diets with different energy and protein sources by use of reticular and omasal sampling

This study aimed to evaluate the effects of different traditional or alternative energy and protein sources, associated or not, on feeding behavior, ruminal kinetics, and post-ruminal flow of nutrients. Besides, it was assessed diets' effects on different sites (reticulum and omasum) of buffaloes. Four ruminally cannulated male Murrah buffaloes (average initial weight of 637 ± 66.37 kg) were randomly distributed in a 4 × 4 Latin square design. Treatments were arranged as 2 × 2 factorial arrangement. The first factor evaluated was the inclusion of energy sources (ground corn and crude glycerin), and the second factor was the inclusion of protein sources (soybean meal and cottonseed cake). Buffaloes fed cottonseed cake had a higher content of neutral detergent fiber (NDF) and potentially digestible detergent fiber (pdNDF) in the rumen environment than buffaloes fed soybean meal. There was a sampling site effect on rumen digestion rates of pdNDF, passage rates of indigestible neutral detergent fiber (iNDF), and pdNDF, and flow of iNDF. In this study, omasal collections were more representative. Total replacement of ground corn by crude glycerin promoted less NDF ruminal digestibility, and care should be taken to include this energy source. The cottonseed cake does not cause a difference in rumen dynamics and can totally replace soybean meal in feedlot buffaloes' diet.

Effect of increasing dietary protein with constant lysine:methionine ratio on production and omasal flow of nonammonia nitrogen in lactating dairy cows

Eight lactating cows were fed 4 diets in which dietary crude protein (CP) was increased in steps of approximately 2 percentage units from 11 to 17% of DM by replacing high-moisture corn with soybean meal supplemented with rumen-protected Met to maintain a Lys:Met ratio of 3:1 in metabolizable protein. Trial design was a replicated 4 × 4 Latin square; experimental periods lasted 28 d, with data and sample collection being performed during wk 3 and 4 of each period. Digesta samples were collected from the rumen as well as the omasum to measure metabolite concentrations and ruminal outflow of N fractions using infusion of ¹⁵N-enriched ammonia to quantify microbial nonammonia N (NAN) and nonmicrobial NAN. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc.). There were linear increases in the yields of milk and true protein and concentration of milk urea N, and a linear decrease in N efficiency, with increasing dietary CP. Apparent ruminal and total-tract N digestibility increased linearly with increasing dietary CP, but estimated true total-tract N digestibility was not affected. Apparent digestibility of the other macronutrients was not influenced by diet. Ruminal ammonia, total AA and peptides, and branched-chain VFA also increased linearly with dietary CP. The ¹⁵N enrichment of liquid- and particle-associated microbes linearly declined with increasing dietary CP due to decreasing ¹⁵N enrichment of the ammonia pool. Although no effect of dietary CP on nonmicrobial NAN flow was detected, total NAN flow increased linearly from 525 g/d at 11% CP to 637 g/d at 17% CP due to the linear increase in microbial NAN flow from 406 g/d at 11% CP to 482 g/d at 17% CP. Under the conditions of this study, when dietary CP was increased by adding soybean meal supplemented with rumen-protected Met, improved milk and protein yields were driven not by RUP supply but by increased ruminal outflow of microbial protein.

Microbial composition and omasal flows of bacterial, protozoal, and nonmicrobial amino acids in lactating dairy cows fed fresh perennial ryegrass (Lolium perenne L.) not supplemented or supplemented with rolled barley

The objective of this study was to evaluate the effect of rolled barley supplementation on microbial composition and omasal flows of bacterial, protozoal, and nonmicrobial AA in cows fed fresh perennial ryegrass (Lolium perenne L.; PRG). Ten ruminally cannulated multiparous Holstein cows averaging (mean ± standard deviation) 49 ± 23 d in milk and 513 ± 36 kg of body weight were assigned to 1 of 2 treatments in a switchback design. The treatment diets were PRG only or PRG plus 3.5 kg of dry matter rolled barley (G+RB). The study consisted of three 29-d periods where each period consisted of 21 d of diet adaptation and 8 d of data and sample collection. A double-marker system was used to quantify nutrient flow entering the omasal canal along with ¹⁵N-ammonium sulfate to label and measure the microbial and nonmicrobial omasal flow of AA. Overall, rolled barley supplementation had no effect on the AA composition of the omasal liquid-associated and particle-associated bacteria. Rolled barley supplementation affected the AA concentrations of omasal protozoa; however, the differences were nutritionally minor. Particle-associated bacteria AA flow was increased for all AA, except for Trp and Pro, in cows fed the G+RB diet. Rolled barley supplementation had no effect on protozoal AA flow. On average, protozoa accounted for 23% of the microbial essential AA flow, which ranged from 17 to 28% for Trp and Lys, respectively. The flow of all AA in omasal true digesta increased in cows fed the G+RB diet compared with the PRG-only diet, resulting in a 228 g/d increase in total AA flow in cows fed the G+RB diet. This increase in total AA flow in cows fed the G+RB diet was due to an increase in microbial AA flow. Rolled barley supplementation had no effect on nonmicrobial AA flow. The nonmicrobial AA flow modestly contributed to total AA flow, accounting for 15.6% on average. These results indicated that extensive ruminal degradation of PRG AA occurred (83.5%), and we demonstrated that cows consuming PRG-based diets exhibit a large dependence on microbial AA to support metabolizable AA supply. Rolled barley supplementation can increase the omasal flow of microbial AA in cows consuming PRG-based diets. However, further research is required to elucidate if this increased AA supply can support higher milk yield under such dietary conditions.

Effects of bismuth subsalicylate and encapsulated calcium ammonium nitrate on ruminal fermentation of beef cattle

A replicated 5 × 5 Latin square design with a 2 × 2 + 1 factorial arrangement of treatments was used to determine the effects of bismuth subsalicylate (BSS) and encapsulated calcium ammonium nitrate (eCAN) on ruminal fermentation of beef cattle consuming bahiagrass hay (Paspalum notatum) and sugarcane molasses. Ten ruminally cannulated steers (n = 8; 461 ± 148 kg of body weight [BW]; average BW ± SD) and heifers (n = 2; 337 ± 74 kg of BW) were randomly assigned to one of five treatments as follows: 1) 2.7 g/kg of BW of molasses (NCTRL), 2) NCTRL + 182 mg/kg of BW of urea (U), 3) U + 58.4 mg/kg of BW of BSS (UB), 4) NCTRL + 538 mg/kg of BW of eCAN (NIT), and 5) NIT + 58.4 mg/kg of BW of BSS (NITB). With the exception of NCTRL, all treatments were isonitrogenous. Beginning on day 14 of each period, ruminal fluid was collected and rectal temperature was recorded 4× per day for 3 d to determine ruminal changes every 2 h from 0 to 22 h post-feeding. Ruminal gas cap samples were collected at 0, 3, 6, 9, and 12 h on day 0 of each period followed by 0 h on days 1, 2, 3, and 14. Microbial N flow was determined using Cr-Ethylenediaminetetraacetic acid, YbCl3, and indigestible neutral detergent fiber for liquid, small particle, and large particle phases, respectively. Data were analyzed using the MIXED procedure of SAS. Orthogonal contrasts were used to evaluate the effects of nonprotein nitrogen (NPN) inclusion, NPN source, BSS, and NPN source × BSS. There was no treatment effect (P > 0.05) on concentrations of H2S on day 0, 1, 2, or 14; however, on day 3, concentrations of H2S were reduced (P = 0.018) when NPN was provided. No effect of treatment (P = 0.864) occurred for ruminal pH. There was an effect of NPN source on total concentrations of VFA (P = 0.011), where a 6% reduction occurred when eCAN was provided. There were effects of NPN (P = 0.001) and NPN source (P = 0.009) on the concentration of NH3-N, where cattle consuming NPN had a greater concentration than those not consuming NPN, and eCAN reduced the concentration compared with urea. Total concentrations of VFA and NH3-N were not affected (P > 0.05) by BSS. There was an effect of BSS (P = 0.009) on rectal temperature, where cattle not consuming BSS had greater temperatures than those receiving BSS. No differences for NPN, NPN source, nor BSS (P > 0.05) were observed for microbial N flow. In conclusion, eCAN does not appear to deliver equivalent ruminal fermentation parameters compared with urea, and BSS has limited effects on fermentation.

Between-cow variation in milk fatty acids associated with methane production

We evaluated the between-cow (b-cow) variation and repeatability in omasal and milk fatty acids (FA) related to methane (CH4) emission. The dataset was originated from 9 studies with rumen-cannulated dairy cows conducted using either a switch-back or a Latin square design. Production of CH4 per mole of VFA (Y_CH4VFA) was calculated based on VFA stoichiometry. Experiment, diet within experiment, period within experiment, and cow within experiment were considered as random factors. Empirical models were developed between the variables of interest by univariate and bivariate mixed model regression analysis. The variation associated with diet was higher than the b-cow variation with low repeatability (< 0.25) for milk odd- and branch-chain FA (OBCFA). Similarly, for de novo synthesized milk FA, diet variation was ~ 3-fold greater than the b-cow variation; repeatability for these FA was moderate to high (0.34-0.58). Also, for both cis-9 C18:1 and cis-9 cis-12 cis-15 C18:3 diet variation was more than double the b-cow variation, but repeatability was moderate. Among the de novo milk FA, C4:0 was positively related with stoichiometric Y_CH4VFA, while for OBCFA, anteiso C15:0 and C15:0 were negatively related with it. Notably, when analyzing the relationship between omasal FA and milk FA we observed positive intercept estimates for all the OBCFA, which may indicate endogenous post-ruminal synthesis of these FA, most likely in the mammary gland. For milk iso C13:0, iso C15:0, anteiso C15:0, and C15:0 were positively influenced by omasal proportion of their respective FA and by energy balance. In contrast, the concentration of milk C17:0, iso C18:0, C18:0, cis-11 C18:1, and cis-9 cis-12 cis-15 C18:3 were positively influenced by omasal proportion of their respective FA but negatively related to calculated energy balance. Our findings demonstrate that for most milk FA examined, a larger variation is attributed to diet than b-cow differences with low to moderate repeatability. While some milk FA were positively or negatively related with Y_CH4VFA, there was a pronounced effect of calculated energy balance on these estimates. Additionally, even though OBCFA have been indicated as markers of rumen function, our results suggest that endogenous synthesis of these FA may occur, which therefore, may limit the utilization of milk FA as a proxy for CH4 predictions for cows fed the same diet.

Effects of Capsicum and Propyl-Propane Thiosulfonate on Rumen Fermentation, Digestion, and Milk Production and Composition in Dairy Cows

Essential oils may affect rumen fermentation, nutrient digestion, and milk production and composition. The objective of this study was to test the effects of capsicum oleoresin (CAP) and propyl-propane thiosulfonate (PTSO) on rumen fermentation, total tract digestibility, and milk yield and composition in lactating dairy cattle. Six lactating Holstein cows (averaging (mean ± SD) 130 ± 40 days in milk and 723 ± 55 kg of body weight) fitted with rumen cannulae were used in a duplicated 3 × 3 Latin square design. Treatments were: a control diet (CTR), the CTR diet with the addition of 500 mg/d/cow of CAP, and the CTR diet with the addition of 250 mg/d/cow of PTSO. Dry matter intake (DMI) averaged 20.7 kg/d with a tendency towards higher intake in cows fed CAP and lower in those fed PTSO (p = 0.08). Milk yield averaged 31.8 kg/d with no difference among treatments. However, feed efficiency was higher in PTSO supplemented cows compared with CTR (1.65 and 1.41 kg of milk yield/kg of DMI, respectively; p < 0.01). At the doses used in this experiment, CAP and PTSO failed to demonstrate any effects on rumen fermentation, but PTSO increased the efficiency of feed utilization to produce milk.

Body weight and sex effects on digesta mean retention time in growing Saanen goats

Despite the important role of digesta mean retention time (MRT) on digestive efficiency of ruminants, it is poorly investigated in total gastrointestinal tract (GIT) of growing ruminants, especially in goats. The objective of this study was to evaluate the effect of body weight (BW) and sex on GIT MRT of particles and solutes in growing Saanen goats. A dataset from two studies, comprising 103 individual records of castrated males (n = 36), females (n = 34), and intact males (n = 33) Saanen goats slaughtered at 15, 22, 30, 37, and 45 kg BW, was used. Goats were fed basically with total mixed ration composed by dehydrated corn plant (Zea mays) milled to pass a 10-mm screen, cracked corn grain, and soybean (Glycine max) meal. Variables evaluated were BW, feed intake, feed intake level, composition of ingested diet, wet weight of GIT tissues, wet digesta pool size, digesta composition (dry matter and neutral detergent fiber [NDF]), indigestible NDF:NDF ratio of ingested diet and GIT digesta, MRT of particles (MRT_iNDF) and solutes (MRT_Cr), and reticulorumen selectivity factors (large particles/solutes). Reticulorumen, omasum, abomasum, small intestine, cecum, and colon-rectum segments were evaluated. The dataset was analyzed as mixed models considering sex, BW, and sex × BW interaction as fixed effects, and study and residual error as random effects. Sex did not affect MRT_iNDF in any GIT segments. Females and intact males presented similar reticulorumen MRT_Cr (5.6 h; P = 0.92) and they presented lower reticulorumen MRT_Cr than castrated males (7.0; P ≤ 0.04). Total GIT MRT_Cr was similar between castrated males and females (15.7 h; P = 0.11) and between females and intact males (14.2 h; P = 0.76). Body weight (BW) did not affect MRT_iNDF in reticulorumen and colon-rectum and total GIT MRT_Cr (P ≥ 0.11). Reticulorumen and omasum MRT_Cr increased as BW increased (P < 0.01), and abomasum MRT_Cr decreased as BW increased (P = 0.02). Feed intake, and wet tissues and wet pool size of all GIT segments increased as BW increased, except abomasum wet pool size (P ≤ 0.01). The mechanism related to sex effect on MRT has to be elucidated. Reticulorumen MRT_iNDF and total GIT MRT_Cr were modulated by intake and capacity of reticulorumen and GIT, respectively. On the other hand, reticulorumen MRT_Cr seemed to be regulated by reticulo-omasal orifice opening and saliva secretion.

Comparison of microbial fermentation data from dual-flow continuous culture system and omasal sampling technique: A meta-analytical approach

Although the omasal sampling technique (OST) has been successfully used to estimate ruminal fermentation and nutrient flow, alternatives to invasive animal trials should be pursued and evaluated. The objective of this study was to evaluate carbohydrate and N metabolisms using a meta-analytical approach to compare 2 methods: dual-flow continuous culture system (DFCCS) and OST. To be included, studies needed to report diet chemical composition and report at least 1 of the dependent variables of interest. A total of 155 articles were included, in which 97 used the DFCCS and 58 used the OST. The independent variables used were dietary nonfiber carbohydrate concentration, neutral detergent fiber (NDF) degradability, true crude protein (CP) degradability, and efficiency of microbial protein synthesis (EMPS). In addition, 12 dependent variables were used. Statistical analyses were performed using the Mixed procedure of SAS (SAS Institute Inc., Cary, NC). A random coefficients model was used considering study as a random effect and including the possibility of covariance between the slope and the intercept. The effect of method (DFCCS or OST) was included and tested in the estimates of the intercept, linear, and quadratic effects of the independent variable. There was no method effect when NDF degradability was regressed with total volatile fatty acids concentration, true CP degradability, and EMPS. Molar proportions of acetate and propionate were quadratically associated with NDF degradability. When NDF degradability was regressed with acetate and propionate there was a method effect, differing only in the intercept (β₀) estimate. True organic matter digestibility, bacterial N/total N, efficiency of N utilization, total volatile fatty acid concentration, and molar proportion of butyrate linearly increased as dietary nonfiber carbohydrate concentration increased, and none of these variables were affected by method. Concentration of ammonia N had a linear and positive association with true CP degradability. This was the only variable that had a method effect when regressed with true CP degradability, differing only in the estimate of the intercept (β₀). As EMPS increased, efficiency of N utilization also increased, and it was affected by method. Overall, the majority of DFCCS responses were similar to OST. When a method effect was observed, it was mainly on the estimate of the intercept, demonstrating that the magnitude of these responses was different. However, the relationships between independent and dependent variables were similar across methods.

The effect of dietary forage to concentrate ratio and forage type on milk fatty acid composition and milk fat globule size of lactating cows

We examined the effects of 2 grass silage-based diets differing in forage:concentrate (FC) ratio and those of a red clover silage-based diet on intake, milk production, ruminal fatty acid (FA) biohydrogenation, milk FA composition, and milk fat globule (MFG) size distribution. Ten multiparous Nordic Red cows received the following treatments: grass silage-based diets containing high (70:30, HG) or low (30:70, LG) FC ratio or a red clover silage-based diet with an FC ratio of 50:50 (RC) on a dry matter basis. Determinations of MFG were performed from fresh milk samples without addition of EDTA so the results of fat globules >1 µm in diameter are emphasized instead of the entire globule population. Lower FC ratio in grass silage-based diets increased milk production with no effect on daily fat yield, leading to 13% lower milk fat concentration. The effect of FC ratio on MFG size was moderate. It did not affect the volume-weighted diameter in grass silage-based diets, although LG lowered the volume-surface diameter of MFG in the size class >1 µm compared with HG. Compared with HG, feeding LG moderately decreased the biohydrogenation of 18:2n-6, leading to a higher level of polyunsaturated fatty acids in milk fat. Feeding RC lowered milk fat concentration and daily milk fat yield compared with grass silage-based diets. The volume-weighted diameter of MFG in the size class >1 µm was smaller in RC milk compared with grass silage-based diets. Feeding RC increased the flow of 18:3n-3 at the omasum by 2.4-fold and decreased the apparent ruminal 18:3n-3 biohydrogenation compared with grass silage-based diets despite similar intake of 18:3n-3. It also resulted in the lowest amount of saturated FA and the highest amounts of cis-9 18:1, 18:3n-3, and polyunsaturated FA in milk. In conclusion, LG decreased milk fat content and induced minor changes in MFG size distribution compared with HG, whereas RC lowered milk fat production, altered milk FA composition to nutritionally more beneficial direction, and led to smaller MFG compared with grass silage-based diets.

Ruminal fatty acid outflow in dry cows fed different sources of linoleic acid: reticulum and omasum as alternative sampling sites to abomasum

This study was designed to determine the rumen outflow of fatty acids (FA) and biohydrogenation (BH) extent using alternative sampling sites (reticulum and omasum) to abomasum in dry cows fed different sources of FA. Four Holstein non-pregnant dry cows (≥3 parturitions, and 712 ± 125 kg BW), cannulated in the rumen and abomasum, were randomly assigned to a 4 × 4 Latin square design experiment, containing the following treatments: 1) control (CON); 2) soya bean oil (SO), dietary inclusion at 30 g/kg; 3) whole raw soya beans (WS), dietary inclusion at 160 g/kg; and 4) calcium salts of FA (CSFA), dietary inclusion at 32 g/kg. Rumen outflow of nutrients was estimated using the three markers reconstitution system (cobalt-EDTA, ytterbium chloride, and indigestible neutral detergent fibre [NDF]). Diets with FA sources decreased feed intake and increased FA intake. No differences in nutrient intake and digestibility were detected among cows fed diets supplemented with different FA sources. Diets with FA sources reduced the rumen outflow of DM and NDF, hence decreasing their passage rates. In addition, SO diet reduced the ruminal outflow of DM and NDF in comparison with WS and CSFA. Omasal sampling yielded the highest values of rumen outflow of NDF and potentially degradable NDF (pdNDF), whereas the reticular and abomasal samplings yielded intermediate and least values, respectively. The interaction effect between diet and sampling site was observed for rumen outflow of majority FA (except for C16:0, C18:0, and C18:2 trans-10, cis-12) and BH extension of C18:1 cis, C18:2, and C18:3. Calculations derived from abomasal sampling revealed that WS and CSFA diets had lower BH extent of C18:1 cis and C18:2 in comparison with SO, whereas cows fed CSFA had greater BH extent of C18:3 and lower BH extent of C18:1 cis compared to those fed WS. However, the latter results were not similar when calculations were performed based on the reticular and omasal samplings. Thus, there is evidence that neither reticular nor omasal samplings are suitable for estimating rumen outflow of FA in dry cows. In addition, WS and CSFA diets can increase the abomasal flow of polyunsaturated FA in dry cows.

Effect of variety and level of inclusion of barley silage selected for varying neutral detergent fiber digestibility on ruminal fermentation and nutrient digestibility in feedlot heifers fed backgrounding and finishing diets

Two metabolism studies were conducted to evaluate the effect of variety and level of inclusion of barley silage on ruminal fermentation and total tract nutrient digestibility using beef heifers fed backgrounding (Study 1) and finishing (Study 2) diets. Both studies were 4 × 4 Latin square designs with a 2 × 2 factorial arrangement (barley varieties, CDC Cowboy and Xena; levels of inclusion, LOW and HIGH). Barley varieties did not vary in 30 h neutral detergent fiber (NDF) digestibility and averaged 37.1% ± 1.86% (% of NDF) across varieties. Heifers fed CDC Cowboy had greater (P = 0.05) mean ruminal pH and a lower (P = 0.01) duration under pH 5.8 relative to those fed Xena in Study 1, whereas heifers fed HIGH-silage diets had lower (P = 0.05) duration under ruminal pH 5.8 than those fed LOW-silage diets in Study 2. Variety of barley had minimal impact on ruminal fermentation and total tract nutrient digestibility in heifers fed barley silage, although high NDF content decreased energy intake. High NDF barley varieties and greater inclusion levels also increased ruminal pH which may improve total tract fiber digestibility in heifers fed finishing diets.

Nitrogen utilization, whole-body urea-nitrogen kinetics, omasal nutrient flow, and production performance in dairy cows fed lactose as a partial replacement for barley starch

The objective of this study was to determine whether the partial replacement of barley starch with lactose (fed as dried whey permeate; DWP) affects N utilization, whole-body urea kinetics, and production in dairy cows. Eight lactating Holstein cows were used in a replicated 4 × 4 Latin square design with 28-d periods. Four cows in one Latin square were ruminally cannulated and used to determine dietary effects on whole-body urea kinetics and N utilization. Cows were fed a barley-based diet that contained 3.6% (dry matter basis) total sugar (TSG; designated control), or diets that contained 6.6, 9.6, or 12.6% TSG. Dietary TSG content was increased by the replacement of barley grain with DWP (83% lactose). Diets were isonitrogenous (∼17.3% crude protein), and starch contents of the control, 6.6, 9.6, and 12.6% TSG diets were 24.3, 22.2, 21.2, and 19.1%, respectively. Whole-body urea kinetics were measured using 4-d infusions of [¹⁵N¹⁵N]-urea with concurrent total collections of feces and urine. Dry matter intake (mean = 26.7 kg/d), milk yield (mean = 34.9 kg/d), and milk protein and fat contents were unaffected by diet. Ruminal ammonia-N concentration decreased linearly as TSG content increased, whereas ruminal butyrate concentration increased linearly as TSG content increased. Urinary excretion of total N and urea-N changed quadratically, whereas urinary excretion of total N (% of N intake) tended to change quadratically as TSG content increased. Fecal N excretion linearly increased as TSG content increased. A quadratic response was observed for total N excretion as TSG content increased. Milk N and retained N were not affected by diet. As TSG content increased, we observed quadratic responses in the omasal flow of fluid-associated and total bacterial nonammonia N, endogenous production of urea-N, urea-N recycled to the gastrointestinal tract, and urea-N returned to the ornithine cycle. Dietary TSG content did not affect the anabolic utilization of recycled urea-N or the proportion of recycled urea-N that was used for bacterial growth. Our results indicate that feeding DWP did not influence dry matter intake, milk yield, or milk composition. Feeding DWP decreased ruminal ammonia-N concentration, but this did not result in positive responses in milk protein secretion or N balance. The quadratic response in omasal flow of total bacterial nonammonia N indicated that including TSG beyond 9.6% of diet dry matter might depress ruminal microbial protein synthesis.

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.

Effect of exogenous butyrate on the gastrointestinal tract of sheep. I. Structure and function of the rumen, omasum, and abomasum

The aim of this study was to determine the effect of exogenous butyrate on the structure and selected functions of the stomach in sheep. Eighteen rams (30.8 ± 2.1 kg; 12 to 15 mo of age) were allocated to the study and fed a diet for 14 d without (CTRL) or with sodium butyrate (BUT; 36 g/kg of offered DM). Neither DMI nor initial BW differed between treatments (P ≥ 0.61), but final BW was greater for BUT compared with CTRL (P = 0.03). Butyrate concentration in the reticuloruminal fluid and abomasal digesta was greater for BUT compared with CTRL (P ≤ 0.01), but total short-chain fatty acids (SCFA) concentration, as well as concentration of other SCFA, did not differ between treatments (P ≥ 0.07). Relative to BW, reticuloruminal tissue mass tended (P = 0.09) to be greater and omasal digesta was less (P = 0.02) for BUT compared with CTRL. Dietary butyrate did not affect ruminal papillae length, width, and density nor did it affect ruminal epithelium thickness (P ≥ 0.12) in the ventral sac of the rumen. However, the DM of ruminal epithelium (mg/cm2) tended (P = 0.06) to be greater for BUT compared with CTRL. Omasal and abomasal epithelium thicknesses were greater (P ≤ 0.05) for BUT compared with CTRL. Mitosis-to-apoptosis ratio in the abomasal epithelium was less for BUT compared with CTRL (P = 0.04). Finally, the mRNA expression of peptide transporter 1 in the omasal epithelium was less (P = 0.02) and mRNA expression of monocarboxylate transporter 1 in the abomasal epithelium tended (P = 0.07) to be greater for BUT compared with CTRL. It can be concluded that exogenous butyrate supplementation affected not only the rumen but also omasum and abomasum in sheep.

Effects of feeding corn silage from short-season hybrids and extending the backgrounding period on production performance and carcass traits of beef cattle

Corn silage (CS) acreage in western Canada continues to expand with CS being used increasingly in feedlot cattle diets where barley silage (BS) previously was the main forage fed. Our study evaluated the effects of increasing the amounts of CS in backgrounding (BKGN) diets on performance of cattle by 1) replacing BS with early-maturing CS, 2) increasing the proportion of CS in the diet, and 3) extending the BKGN duration. A total of 160 steers (mean BW ± SD; 272 ± 22.4 kg) were used in a completely randomized design. Steers were assigned to 16 pens and fed BKGN diets (4 pens per diet) that contained 60% BS (DM basis; CON), 60% CS (60CS), 75% CS (75CS), or 90% CS (90CS) until reaching a mean pen BW of either 380 (SBKGN) or 430 ± 15 kg (LBKGN) with 2 pens per treatment. All steers were finished (FIN diet; 9% CS, 86% barley grain, and 5% supplement) to an equal-BW end point (700 ± 15 kg LW). During BKGN and FIN phases, DMI, ADG, and G:F were measured for all pens. Carcass data also were collected. No BKGN diet × duration interactions were statistically significant (P ≥ 0.412) for most production measures. As dietary CS content was increased during BKGN, DMI and ADG decreased (quadratic; P ≤ 0.003). There also was a tendency (P = 0.078) for a decrease in G:F at the highest level of CS. As expected, LBKGN steers took longer (105 vs. 71 d; P = 0.001) than SBKGN steers to reach the BKGN target end weight. In addition, as a result of their heavier weight at the beginning of FIN, LBKGN steers also had a higher DMI (11.6 vs. 11.0 kg/d; P = 0.045) than SBKGN steers. However, no carryover effects (P ≥ 0.354) of BKGN diet on DMI, ADG, and G:F were significant during the FIN phase. Similarly, the BKGN diet and duration had no effect (P ≥ 0.219) on carcass traits including HCW, dressing percentage, and quality grade. However, we detected an interaction between BKGN diet and duration on backfat thickness (P = 0.009); SBKGN steers that were fed 75CS during BKGN accumulated more backfat during FIN than LBKGN steers that were fed 75CS during BKGN, and because they were lighter at the beginning of FIN they took longer to reach 700 kg BW, their end point. In conclusion, dietary inclusion of CS (up to 90% of diet DM) in place of BS and extending the BKGN period had marginal effects on FIN performance or carcass traits in our study. Therefore, beef producers can make extensive use of early-maturing CS in growing cattle diets without compromising animal performance or carcass quality.

A 100-Year Review: Protein and amino acid nutrition in dairy cows

Considerable progress has been made in understanding the protein and amino acid (AA) nutrition of dairy cows. The chemistry of feed crude protein (CP) appears to be well understood, as is the mechanism of ruminal protein degradation by rumen bacteria and protozoa. It has been shown that ammonia released from AA degradation in the rumen is used for bacterial protein formation and that urea can be a useful N supplement when lower protein diets are fed. It is now well documented that adequate rumen ammonia levels must be maintained for maximal synthesis of microbial protein and that a deficiency of rumen-degradable protein can decrease microbial protein synthesis, fiber digestibility, and feed intake. Rumen-synthesized microbial protein accounts for most of the CP flowing to the small intestine and is considered a high-quality protein for dairy cows because of apparent high digestibility and good AA composition. Much attention has been given to evaluating different methods to quantify ruminal protein degradation and escape and for measuring ruminal outflows of microbial protein and rumen-undegraded feed protein. The methods and accompanying results are used to determine the nutritional value of protein supplements and to develop nutritional models and evaluate their predictive ability. Lysine, methionine, and histidine have been identified most often as the most-limiting amino acids, with rumen-protected forms of lysine and methionine available for ration supplementation. Guidelines for protein feeding have evolved from simple feeding standards for dietary CP to more complex nutrition models that are designed to predict supplies and requirements for rumen ammonia and peptides and intestinally absorbable AA. The industry awaits more robust and mechanistic models for predicting supplies and requirements of rumen-available N and absorbed AA. Such models will be useful in allowing for feeding lower protein diets and increased efficiency of microbial protein synthesis.

Effects of replacing soybean meal with canola meal or treated canola meal on ruminal digestion, omasal nutrient flow, and performance in lactating dairy cows

Extrusion treated canola meal (TCM) was produced in an attempt to increase the rumen-undegraded protein fraction of canola meal (CM). The objective of this study was to evaluate the effects of replacing soybean meal (SBM) with CM or TCM on ruminal digestion, omasal nutrient flow, and performance in lactating dairy cows. To assess performance, 30 multiparous Holstein cows averaging (mean ± SD) 119 ± 23 d in milk and 44 ± 7 kg of milk/d and 15 primiparous cows averaging 121 ± 19 d in milk and 34 ± 6 kg of milk/d were blocked in a randomized complete block design with a 2-wk covariate period and 12-wk experimental period (experiment 1). Dietary ingredients differed only in protein supplements, which were SBM, CM, or TCM. All diets were formulated to contain (dry matter basis) 30% alfalfa silage, 30% corn silage, 4% soy hulls, 2.4% mineral-vitamin premix, and 16% CP. The SBM diet contained 25% high-moisture shelled corn and 8.6% SBM; the canola diets contained 22% high-moisture shelled corn and either 11.2% CM or 11.4% TCM. To assess ruminal digestion and omasal nutrient flow, 6 rumen-cannulated cows were blocked into 2 squares of 3 cows and randomly assigned within blocks to the same 3 dietary treatments as in experiment 1 in a replicated 3 × 3 Latin square design (experiment 2). Data were analyzed using the MIXED procedure of SAS (SAS Institute, Cary, NC). Orthogonal contrasts were used to compare effects of different protein supplements: SBM versus CM + TCM and CM versus TCM. In experiment 1, compared with SBM, apparent total-tract digestibilities of dry matter and nutrients were greater in cows fed both CM diets, and there was a tendency for nutrient digestibilities to be higher in cows fed CM compared with TCM. Diets did not affect milk yield and milk components; however, both canola diets decreased urinary urea N (% of total urinary N), fecal N (% of total N intake), and milk urea N concentration. In experiment 2, compared with SBM, both canola diets increased N intake and tended to increase rumen-degraded protein supply (kg/d) and N truly digested in the rumen (kg/d). Diets did not affect ruminal digestibility, efficiency of microbial protein synthesis, and rumen-undegraded protein flow among diets. Results from this experiment indicate that replacing SBM with CM or TCM in diets of lactating cows improved digestibility and may reduce environmental impact. Moreover, under the conditions of the present study, treating CM by extrusion did not improve CM utilization.

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.

Physiochemical Characteristics and Molecular Structures for Digestible Carbohydrates of Silages

The main objectives of this study were (1) to assess the magnitude of differences among new barley silage varieties (BS) selected for varying rates of in vitro neutral detergent fiber (NDF) digestibility (ivNDFD; Cowboy BS with higher ivNDFD, Copeland BS with intermediate ivNDFD, and Xena BS with lower ivNDFD) with regard to their carbohydrate (CHO) molecular makeup, CHO chemical fractions, and rumen degradability in dairy cows in comparison with a new corn silage hybrid (Pioneer 7213R) and (2) to quantify the strength and pattern of association between the molecular structures and digestibility of carbohydrates. The carbohydrate-related molecular structure spectral data was measured using advanced vibrational molecular spectroscopy (FT/IR). In comparison to BS, corn silage showed a significantly (P < 0.05) higher level of starch and energy content and higher degradation of dry matter (DM). Cowboy BS had lower feeding value (higher indigestible fiber content and lower starch content) and lower DM degradation in the rumen compared to other BS varieties (P < 0.05). The spectral intensities of carbohydrates were significantly (P < 0.05) correlated with digestible carbohydrate content of the silages. In conclusion, the univariate approach with only one-factor consideration (ivNDFD) might not be a satisfactory method for evaluating and ranking BS quality. FT/IR molecular spectroscopy can be used to evaluate silage quality rapidly, particularly the digestible fiber content.

Effect of increasing the proportion of dietary concentrate on gastrointestinal tract measurements and brush border enzyme activity in Holstein steers

The aim of this study was to determine the time course for adaptation of the reticulo-rumen, omasum, abomasum, and small intestine in response to an abrupt increase in the proportion of grain in the diet. Adaptive responses include tissue and digesta mass, small intestinal length, and brush border enzyme activity in the duodenum, proximal jejunum, and ileum. Twenty-five Holstein steers (213 ± 23 kg; 5 to 7 mo of age) were blocked by body weight, and within block were randomly assigned to 1 of 5 treatments: the control diet (CTRL; 92% chopped grass hay and 8% mineral and vitamin supplement on a dry matter basis) or a moderate grain diet (MGD; 50% chopped grass hay, 42% rolled barley grain, and 8% mineral and vitamin supplement) that was fed for 3 (MGD3), 7 (MGD7), 14 (MGD14), or 21 d (MGD21). Dry matter intake was limited to 2.25% of body weight to ensure that changes in dry matter intake did not confound the results. On the last day of the dietary exposure, steers were slaughtered 2 h after feeding. Reticulo-rumen tissue mass and ruminal epithelium mass in the ventral sac of the rumen were not affected by the MGD. Wet reticulo-ruminal digesta mass decreased from CTRL to MGD7 and then increased, but reticulo-ruminal digesta dry matter mass did not differ between treatments. Omasal mass, omasal tissue mass, and omasum digesta mass decreased linearly with the number of days fed MGD, but abomasal tissue mass tended to increase linearly. Duodenal tissue mass tended to increase linearly, and ileal length increased linearly with the number of days fed MGD. Lactase activity in the proximal jejunum increased linearly and maltase activity in duodenum tended to increase linearly with days fed MGD. Aminopeptidase N activity in the proximal jejunum increased cubically with days fed MGD, and dipeptidylpeptidase IV activity in ileum tended to decrease from CTRL to MGD14 and then tended to increase. Adaptation to a diet with a greater proportion of concentrate involves changes in the mass and length of regions of the gastrointestinal tract and brush border enzyme activity. These changes take place gradually over at least 3 wk.

Diet-induced milk fat depression is associated with alterations in ruminal biohydrogenation pathways and formation of novel fatty acid intermediates in lactating cows

The biohydrogenation theory of milk fat depression (MFD) attributes decreases in milk fat in cows to the formation of specific fatty acids (FA) in the rumen. Trans-10, cis-12-CLA is the only biohydrogenation intermediate known to inhibit milk fat synthesis, but it is uncertain if increased ruminal synthesis is the sole explanation of MFD. Four lactating cows were used in a 4×4 Latin square with a 2×2 factorial arrangement of treatments and 35-d experimental periods to evaluate the effect of diets formulated to cause differences in ruminal lipid metabolism and milk fat synthesis on the flow of FA and dimethyl acetal at the omasum. Treatments comprised total mixed rations based on grass silage with a forage:concentrate ratio of 35:65 or 65:35 containing 0 or 50 g/kg sunflower oil (SO). Supplementing the high-concentrate diet with SO lowered milk fat synthesis from -20·2 to -31·9 % relative to other treatments. Decreases in milk fat were accompanied by alterations in ruminal biohydrogenation favouring the trans-10 pathway and an increase in the formation of specific intermediates including trans-4 to trans-10-18 : 1, trans-8, trans-10-CLA, trans-9, cis-11-CLA and trans-10, cis-15-18 : 2. Flow of trans-10, cis-12-CLA at the omasum was greater on high- than low-concentrate diets but unaffected by SO. In conclusion, ruminal trans-10, cis-12-CLA formation was not increased on a diet causing MFD suggesting that other biohydrogenation intermediates or additional mechanisms contribute to the regulation of fat synthesis in the bovine mammary gland.

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.

Effect of dietary fish oil on biohydrogenation of fatty acids and milk fatty acid content in cows

Mechanisms underlying milk fat conjugated linoleic acid (CLA) responses to supplements of fish oil were investigated using five lactating cows each fitted with a rumen cannula in a simple experiment consisting of two consecutive 14-day experimental periods. During the first period cows were offered 18 kg dry matter (DM) per day of a basal (B) diet formulated from grass silage and a cereal based-concentrate (0·6 : 0·4; forage : concentrate ratio, on a DM basis) followed by the same diet supplemented with 250 g fish oil per day (FO) in the second period. The flow of non-esterified fatty acids leaving the rumen was measured using the omasal sampling technique in combination with a triple indigestible marker method based on Li-Co-EDTA, Yb-acetate and Cr-mordanted straw. Fish oil decreased DM intake and milk yield, but had no effect on milk constituent content. Milk fat trans-11 C18:1, total trans-C18 : 1, cis-9 trans-11 CLA, total CLA, C18 : 2(n-6) and total C18 : 2content were increased in response to fish oil from 1·80, 4·51, 0·39, 0·56, 0·90 and 1·41 to 9·39, 14·39, 1·66, 1·85, 1·25 and 4·00 g/100 g total fatty acids, respectively. Increases in the cis-9, trans-11 isomer accounted for proportionately 0·89 of the CLA response to fish oil. Furthermore, fish oil decreased the flow of C18 : 0(283 and 47 g/day for B and FO, respectively) and increased that of trans-C18 : 1fatty acids entering the omasal canal (38 and 182 g/day). Omasal flows of trans-C18 : 1acids with double bonds in positions from delta-4 to -15 inclusive were enhanced, but the effects were isomer dependent and primarily associated with an increase in trans-11 C18 : 1 leaving the rumen (17·1 and 121·1 g/day for B and FO, respectively). Fish oil had no effect on total (4·36 and 3·50 g/day) or cis-9, trans-11 CLA (2·86 and 2·08 g/day) entering the omasal canal. Flows of cis-9, trans-11 CLA were lower than the secretion of this isomer in milk. Comparison with the transfer of the trans-9, trans-11 isomer synthesized in the rumen suggested that proportionately 0·66 and 0·97 of cis-9, trans-11 CLA was derived from endogenous conversion of trans-11 C18 : 1in the mammary gland for B and FO, respectively. It is concluded that fish oil enhances milk fat cis-9, trans-11 CLA content in response to increased supply of trans-11 C18:1that arises from an inhibition of trans-C18 : 1reduction in the rumen.

Effect of including high-lipid by-product pellets in substitution for barley grain and canola meal in finishing diets for beef cattle on ruminal fermentation and nutrient digestibility

The objective was to determine the effect of replacing barley grain and canola meal with high-lipid by-product pellets (HLBP; 14.6% CP, 29.8% NDF, 9.0% fat, and 5.52 MJ NE/kg in DM) on DMI, ruminal fermentation, nutrient flow at the omasal canal, and nutrient digestibility. Four ruminally cannulated and ovariectomized Hereford × Gelbvieh heifers (initial BW of 631.9 ± 23.3 kg; mean ± SD) were used in a 4 × 4 Latin square design. Periods consisted of 28 d, including 10 d for diet transition, 11 d for dietary adaptation, and 7 d for measurements. Heifers were fed a typical finishing diet consisting of 89% of concentrate (barley grain and canola meal; CONT), 6% of barley silage, and 5% of mineral and vitamin supplement (on DM basis). Dietary treatments consisted of a CONT or diets where 30% (HLBP30), 60% (HLBP60), and 90% (HLBP90) of the barley grain and canola meal were replaced with HLBP. Dry matter intake was not affected by treatment ( > 0.10). Total short-chain fatty acid concentration and molar proportions of acetate, propionate, and butyrate ( > 0.10) among treatments and ruminal ammonia did not differ ( > 0.10) among treatments, and ruminal ammonia increased ( = 0.03) linearly with increasing HLBP inclusion rate in the diet. Mean and maximum pH increased, whereas the duration and area that pH was below 5.8, 5.5, and 5.2, thresholds used for mild, severe, and acute ruminal acidosis, respectively, decreased linearly ( ≤ 0.05) with increasing rates of inclusion of HLBP. Organic matter flow at the omasal canal increased linearly ( = 0.03) with increasing HLBP inclusion rate in the diet. However, OM digestibility coefficients and apparent ruminal NDF and ADF digestibility yielded negative values for some animals, especially those fed HLBP90, indicating that ruminal digestibility was underestimated. Total tract OM digestibility decreased linearly ( < 0.01) with increasing inclusion rates of HLBP. This study showed that HLBP inclusion in substitution for barley grain and canola meal linearly decreases the severity of ruminal acidosis in cattle fed a typical grain-based finishing diet. However, total tract nutrient digestibility was negatively affected.

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 Cornell Net Carbohydrate and Protein System: Updates to the model and evaluation of version 6.5

New laboratory and animal sampling methods and data have been generated over the last 10 yr that had the potential to improve the predictions for energy, protein, and AA supply and requirements in the Cornell Net Carbohydrate and Protein System (CNCPS). The objectives of this study were to describe updates to the CNCPS and evaluate model performance against both literature and on-farm data. The changes to the feed library were significant and are reported in a separate manuscript. Degradation rates of protein and carbohydrate fractions were adjusted according to new fractionation schemes, and corresponding changes to equations used to calculate rumen outflows and postrumen digestion were presented. In response to the feed-library changes and an increased supply of essential AA because of updated contents of AA, a combined efficiency of use was adopted in place of separate calculations for maintenance and lactation to better represent the biology of the cow. Four different data sets were developed to evaluate Lys and Met requirements, rumen N balance, and milk yield predictions. In total 99 peer-reviewed studies with 389 treatments and 15 regional farms with 50 different diets were included. The broken-line model with plateau was used to identify the concentration of Lys and Met that maximizes milk protein yield and content. Results suggested concentrations of 7.00 and 2.60% of metabolizable protein (MP) for Lys and Met, respectively, for maximal protein yield and 6.77 and 2.85% of MP for Lys and Met, respectively, for maximal protein content. Updated AA concentrations were numerically higher for Lys and 11 to 18% higher for Met compared with CNCPS v6.0, and this is attributed to the increased content of Met and Lys in feeds that were previously incorrectly analyzed and described. The prediction of postruminal flows of N and milk yield were evaluated using the correlation coefficient from the BLUP (R(2)BLUP) procedure or model predictions (R(2)MDP) and the concordance correlation coefficient. The accuracy and precision of rumen-degradable N and undegradable N and bacterial N flows were improved with reduced bias. The CNCPS v6.5 predicted accurate and precise milk yield according to the first-limiting nutrient (MP or metabolizable energy) with a R(2)BLUP=0.97, R(2)MDP=0.78, and concordance correlation coefficient=0.83. Furthermore, MP-allowable milk was predicted with greater precision than metabolizable energy-allowable milk (R(2)MDP=0.82 and 0.76, respectively, for MP and metabolizable energy). Results suggest a significant improvement of the model, especially under conditions of MP limitation.