Varying degradation rates of total nonstructural carbohydrates: effects on ruminal fermentation, blood metabolites, and milk production and composition in high producing Holstein cows

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.

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.

Orange juice industry by-product silage can increase fat and protein in Holstein cow's milk

We aimed to evaluate the effect of replacing corn silage by orange peel silage on nutrient intake, ruminal parameters and milk production of multiparous lactating Holstein cows. Eight fistulated Holstein cows averaging 587.5 ± 39.6 kg and 111 ± 22 d in milking were randomly assigned to a double 4 × 4 Latin square design carried out two times to determine the effects of feeding with orange peel silage (OPS) in substitution of whole plant corn silage (WPCS). The treatments were a control diet with WPCS only or diets with OPS replacing WPCS in the total mixed diet (250, 500, or 750 g/kg DM). All cows were fed the same 750 : 250 g/kg roughage : concentrate ratio. The DM intake and milk production were reduced with the OPS inclusion, with decreases in consumption of neutral detergent fibre and increased consumption of non-fibrous carbohydrates. Diets with 250 and 500 g/kg OPS showed similar milk production and protein content in milk to the standard WCPS diet, whilst 750 g/kg orange peel silage as roughage increased fat and protein contents significantly. The orange peel silage as a substitute for corn silage for feeding dairy cows did not show adverse changes in the rumen environment and showed promising results in the increase of fat in milk of Holstein cows.

Propylene Glycol and Maize Grain Supplementation Improve Fertility Parameters in Dairy Cows

Simple Summary

The excessive mobilization of fatty acids from dairy cows’ adipose tissue increases blood non-esterified fatty acid concentrations and could have a negative effect on the fertility parameters and milk yield, as well as increase the risk of metabolic disorders and also result in early-lactation culling risk. Propylene glycol and rumen-protected starch from maize grain are commonly used as glucose precursors reducing nonesterified fatty acid levels; however, no such comparisons are available, thus it was decided to assume it as the aim of this study. Propylene glycol had a positive effect on shortening the period to first ovulation. Propylene glycol and maize grain improved the first service conception rate and decreased the number of services per conception in cows. In conclusion, both treatments with propylene glycol and maize grain had a slight effect on the metabolic profile and no effect on milking performance, yet they improved fertility parameters, which could indirectly enhance milk production economics.

Abstract

The aim of the study was to determine the effect of propylene glycol and maize grain content by-pass starch supplementation during the transition period and the first 56 days of lactation on blood metabolic indices, milk production and fertility parameters in dairy cows. Seventy-five Polish Holstein-Friesian dairy cows were assigned to treatment 21 days before calving. The treatments included: TG—2.5 kg triticale grain/cow per day supplemented from 14 days prepartum to day 56 postpartum, PG—2.5 kg triticale grain/cow per day supplemented from day 14 before parturition to day 56 postpartum, and 400 g propylene glycol/cow per day from 14 days prepartum to 14 days of lactation and MG—2.5 kg maize grain/cow per day supplemented from day 14 before parturition to day 56 postpartum. PG and MG had an effect resulting in the highest glucose concentration at 28 d of lactation. Cows assigned to the PG and MG groups had significantly higher cholesterol levels confronted with TG group at day 14 of lactation, while at days 28 and 56 the same difference was observed only between the MG and TG groups. PG had an effect on shortening the period to first ovulation. PG and MG improved the first service conception rate and decreased the number of services per conception in cows. In conclusion, both treatments of dairy cows with PG and MG improved their fertility parameters, while they had a slight effect on their metabolic profile and no effect on their milking performance.

Influence of levels of supplementary concentrate mixture on lactation performance of Red Sokoto does and the pre-weaning growth rate of their kids

•

Concentrate mixture containing palm oil was fed at graded levels to lactating goats

•

Total DMI increased with concentrate level and intake of hay was not compromised

•

Higher concentrate levels improved daily milk yield by 48% with higher persistency of production

•

Dam milk yield accounted for 61% variation in kids pre-weaning daily weight gain

Twenty pregnant Red Sokoto goats (liveweight, 28 ± 1.30 kg) were used in a completely randomized design to determine the effect of varying levels of concentrate on lactation performance. The concentrate, which contained 4% palm oil, was fed at levels of 1.0, 1.5, 2.0 and 2.5% of body weight of the does in addition to a basal diet of Digitaria smutsii hay offered ad libitum. The corresponding dietary treatments were designated as 1.0%C, 1.5%C, 2.0%C and 2.5%C, respectively. The goats were balanced for parity and randomly allocated to give five animals per treatment, and stall-fed individually.

The intake of dry matter and daily milk production linearly and quadratically increased (P<0.05) to the levels of concentrate supplementation. Increase in level of concentrate mixture supplementation affected (P<0.05) milk fat content and milk fat yield, but not other milk constituents. Persistency of milk production was numerically higher at higher levels of concentrate supplementation. Whereas 1.0%C, 1.5%C and 2.0%C could not prevent weight loss in the does, the 2.5%C significantly (P<0.05) promoted average daily gain (11.11 g/head/day) during lactation. The dam milk yield significantly (P<0.01) accounted for 61% of variation in kids pre-weaning average daily gain (ADG). It is concluded that concentrate mixture containing 4% palm oil can be fed at 2.5% of body weight without adverse effect on total dry matter intake, while enhancing postpartum weight gains, higher milk yield, persistency of milk production, pre-weaning growth of kids in Red Sokoto goats.

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

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

Quantifying body water kinetics and fecal and urinary water output from lactating Holstein dairy cows

Reliable estimates of fresh manure water output from dairy cows help to improve storage design, enhance efficiency of land application, quantify the water footprint, and predict nutrient transformations during manure storage. The objective of the study was to construct a mechanistic, dynamic, and deterministic mathematical model to quantify urinary and fecal water outputs (kg/d) from individual lactating dairy cows. The model contained 4 body water pools: reticulorumen (QRR), post-reticulorumen (QPR), extracellular (QEC), and intracellular (QIC). Dry matter (DM) intake, dietary forage, DM, crude protein, acid detergent fiber and ash contents, milk yield, and milk fat and protein contents, days in milk, and body weight were input variables to the model. A set of linear equations was constructed to determine drinking, feed, and saliva water inputs to QRR and fractional water passage from QRR to QPR. Water transfer via the rumen wall was subjected to changes in QEC and total water input to QRR. Post-reticulorumen water passage was adjusted for DM intake. Metabolic water production and respiratory cutaneous water losses were estimated with functions of heat production in the model. Water loss in urine was driven by absorbed N left after being removed via milk. Model parameters were estimated simultaneously using observed fecal and urinary water output data from lactating Holstein cows (n=670). The model was evaluated with data that were not used for model development and optimization (n=377). The observations in both data sets were related to thermoneutral conditions. The model predicted drinking water intake, fecal, urinary, and total fresh manure water output with root mean square prediction errors as a percentage of average values of 18.1, 15.6, 30.6, and 14.6%, respectively. In all cases, >97% of the prediction error was due to random variability of data. The model can also be used to determine saliva production, heat and metabolic water production, respiratory cutaneous water losses, and size of major body water pools in lactating Holstein cows under thermoneutral conditions.

Revised digestive parameter estimates for the Molly cow model

The Molly cow model represents nutrient digestion and metabolism based on a mechanistic representation of the key biological elements. Digestive parameters were derived ad hoc from literature observations or were assumed. Preliminary work determined that several of these parameters did not represent the true relationships. The current work was undertaken to derive ruminal and postruminal digestive parameters and to use a meta-approach to assess the effects of interactions among nutrients and identify areas of model weakness. Model predictions were compared with a database of literature observations containing 233 treatment means. Mean square prediction errors were assessed to characterize model performance. Ruminal pH prediction equations had substantial mean bias, which caused problems in fiber digestion and microbial growth predictions. The pH prediction equation was reparameterized simultaneously with the several ruminal and postruminal digestion parameters, resulting in more realistic parameter estimates for ruminal fiber digestion, and moderate reductions in prediction errors for pH, neutral detergent fiber, acid detergent fiber, and microbial N outflow from the rumen; and postruminal digestion of neutral detergent fiber, acid detergent fiber, and protein. Prediction errors are still large for ruminal ammonia and outflow of starch from the rumen. The gain in microbial efficiency associated with fat feeding was found to be more than twice the original estimate, but in contrast to prior assumptions, fat feeding did not exert negative effects on fiber and protein degradation in the rumen. Microbial responses to ruminal ammonia concentrations were half saturated at 0.2mM versus the original estimate of 1.2mM. Residuals analyses indicated that additional progress could be made in predicting microbial N outflow, volatile fatty acid production and concentrations, and cycling of N between blood and the rumen. These additional corrections should lead to an even more robust representation of the effects of dietary nutrients on ruminal metabolism and nutrient absorption, of animal performance, and the environmental impact of dairy production.

The effect of brown midrib corn silage and dried distillers' grains with solubles on milk production, nitrogen utilization and microbial community structure in dairy cows

Ramirez, H. A. R., Nestor, K., Tedeschi, L. O., Callaway, T. R., Dowd, S. E., Fernando, S. C. and Kononoff, P. J. 2012. The effect of brown midrib corn silage and dried distillers' grains with solubles on milk production, nitrogen utilization and microbial community structure in dairy cows. Can. J. Anim. Sci. 92: 365–380. Thirty-six Holstein cows (24 multiparous and 12 primiparous), four multiparous were ruminally cannulated, (mean±SD, 111±35 days in milk; 664±76.5 kg body weight) were used in replicated 4×4 Latin squares with a 2×2 factorial arrangement of treatments to investigate the effects of brown midrib (bm3) and conventional (DP) corn silages, and the inclusion of dried distillers' grains with solubles (DDGS) on milk production and N utilization. Experimental periods were 28 d in length. Treatments were DP corn silage and 0% DDGS; bm3 corn silage and 0% DDGS; DP corn silage and 30% DDGS; and bm3 corn silage and 30% DDGS. Compared with DP hybrid, total tract fiber digestibility was greater for cows consuming bm3 (32.5 vs. 38.1±1.79%) and DDGS (40.0 vs. 35.2±1.76%). Milk yield was not affected by treatment, and averaged 30.5±1.09 kg d−1. Milk protein yield was positively affected by bm3 corn silage and the inclusion of DDGS. An interaction between hybrid and DDGS on milk fat was also observed. The nature of the interaction was such that milk fat was only affected when DDGS were included in the diet and the lowest milk fat was observed when bm3 corn silage was fed (3.46, 3.59, 2.84 and 2.51±0.10% DP 0% DDGS, bm3 0% DDGS, DP 30% DDGS and bm3 30% DDGS, respectively). As a proportion of the total N consumed, manure N was significantly reduced by the inclusion of bm3 corn silage and DDGS (64.1, 57.1, 52.0, 51.2% for DP 0% DDGS, bm3 0% DDGS, DP 30% DDGS and bm3 30% DDGS, respectively). The Firmicutes:Bacteriodetes ratio in the rumen decreased when cattle consumed DDGS. When cows were fed bm3 corn silage, the population of Fibrobacter sp. tended to represent a larger proportion of the total bacterial population (1.8 vs. 2.3±0.28% for DP and bm3, respectively) and this shift may have been driven by the fact that bm3 corn silage has less lignin, therefore the cellulose digesting bacteria may have more access to the cellulose.

Storage conditions of wet corn distillers' grains with solubles in combination with other feeds and understanding the effects on performance of lactating dairy cows

Ramirez-Ramirez, H. A., Geis, A. R., Heine, C. S., Clark, K. J., Gehman, A. M. and Kononoff, P. J. 2011. Storage conditions of wet corn distillers’ grains with solubles in combination with other feeds and understanding the effects on performance of lactating dairy cows. Can. J. Anim. Sci. 91: 331–339. Wet distillers’ grains are commonly stored in polyethylene silo bags until needed for feeding. The objective of the first experiment was to evaluate the nature of ensiling wet distillers’ grains with soluble (WDGS) alone or in combination with other feeds. A 3×4×3 factorial experiment was conducted in which 36 mixtures were made using three loads of distillers’ grains stored at varying levels with three feeds (corn silage, ground corn, and brome hay). In all mixtures, the addition of feeds to WDGS increased the pH of stored material. The objective of the second experiment was to evaluate the effects of feeding WDGS on milk production. Twenty Holstein cows were used in a 4×5 Youden square. Prior to initiation of the study, WDGS were stored alone (WDGS) or mixed with either 12% ground corn (DM basis) (WDGS+C), 15% brome hay (DM basis) (WDGS+H) or 15% corn silage (DM basis) (WDGS+CS) in polyethylene silo bags. Animals were assigned to one of five treatments during each 21-d period. A diet not containing WDGS was formulated (Control), along with one containing 30% WDGS (DM basis) (WDGS). Three additional diets, similar to the WDGS treatment, were formulated to include one of the three blends of WDGS with corn (WDGS+C), brome hay (WDGS+H) or corn silage (WDGS+CS). Dry matter intake (DMI) was affected by diet and, compared with Control (21.9 kg d−1±0.70 kg d−1), was greater for WDGS (23.8±0.70 kg d−1) and WDGS+C (23.7±0.70 kg d−1). Milk yield, 3.5% FCM, and fat yield were not affected by treatment. These results suggest that dairy rations can be formulated to include stored WDGS at 30% DM without negative effects on milk production and composition.

R, Fernandes J. Efeitos de fontes e formas de processamento do amido na utilização de nutrientes e parâmetros ruminais de vacas em lactação

Cinco vacas holandesas pluríparas, com cânulas no rúmen e no duodeno, foram distribuídas em delineamento de quadrado latino 5 x 5. As vacas foram submetidas a cinco rações experimentais contendo 40% de cana-de-açúcar, 60% de concentrado e cerca de 30% de amido. As rações diferiram quanto ao processamento ou à fonte principal do amido utilizado: milho grosseiramente moído, milho finamente moído, milho floculado a 310g/l, milho floculado a 360g/l ou raspa de mandioca. Não houve diferença (P>0,05) no consumo de matéria seca entre os tratamentos. A digestibilidade ruminal do amido foi maior na ração que continha raspa de mandioca. As digestibilidades ruminal da fibra em detergente neutro e da fibra em detergente ácido não diferiram entre os tratamentos. Os dados médios de pH ruminal se mantiveram acima de 6,0, exceto às 2 e às 4h após a alimentação com a dieta que continha raspa de mandioca. Não houve efeito significativo dos tratamentos sobre a concentração de ácidos graxos voláteis totais. O processo de floculação promoveu aumento da digestibilidade do amido do milho, em relação à moagem de forma grosseira. A digestibilidade ruminal do amido presente na raspa de mandioca foi maior do que a do milho, independentemente da forma de processamento utilizada.

Effect of Alfalfa Silage Storage Structure and Roasting Corn on Production and Ruminal Metabolism of Lactating Dairy Cows

The objective of this study was to determine if feeding roasted corn would improve production and nutrient utilization when supplemented to lactating cows fed 1 of 3 different alfalfa silages (AS). Forty-two lactating Holstein cows (6 fitted with ruminal cannulas) averaging 77 d in milk and 43 kg of milk/d pretrial were assigned to 2 cyclic changeover designs. Treatments were AS ensiled in bag, bunker, or O2-limiting tower silos and supplemented with ground shelled corn (GSC) or roasted GSC (RGSC). Silages were prepared from second-cutting alfalfa, field-wilted an average of 24 h, and ensiled over 2 d. Production and N utilization were evaluated in 36 cows during four 28-d periods, and ruminal fermentation was evaluated with 6 cows during five 21-d periods. Experimental diets contained 40% AS, 15% corn silage, and 35% of either GSC or RGSC on a dry matter basis. No significant interactions between AS and corn sources were detected for any production trait. Although the chemical composition of the 3 AS was similar, feeding AS from the O2-limited tower silo elicited positive production responses. Yields of 3.5% fat-corrected milk and fat were increased 1.7 kg/ d and 150 g/d, and milk fat content was increased 0.3% when cows were fed diets based on AS from the O2-limiting silo compared with the other 2 silages. The responses in milk fat were paralleled by an average increase in acid detergent fiber digestibility of 270 g/d for cows fed AS from the O2-limiting tower silo. However, ruminal concentrations of lipogenic volatile fatty acids were unchanged with AS source. Cows fed RGSC consumed 0.6 kg/d more dry matter and yielded 30 g/ d more protein and 50 g/d more lactose than cows fed GSC diets. There was no evidence of increased total tract digestibility of organic matter or starch, or reduced ruminal NH(3) concentration, when feeding RGSC. Free amino acids increased, and isovalerate decreased in rumen fluid from cows fed RGSC diets. However, responses in production with roasted corn were mainly due to increased dry matter intake, which increased the supply of energy and nutrients available for synthesis of milk and milk components.

Using blood urea nitrogen to predict nitrogen excretion and efficiency of nitrogen utilization in cattle, sheep, goats, horses, pigs, and rats

The objectives of this study were to evaluate the potential for using blood urea N concentration to predict urinary N excretion rate, and to develop a mathematical model to estimate important variables of N utilization for several different species of farm animals and for rats. Treatment means (n = 251) from 41 research publications were used to develop mathematical relationships. There was a strong linear relationship between blood urea N concentration (mg/100 mL) and rate of N excretion (g x d(-1) x kg BW(-1)) for all animal species investigated. The N clearance rate of the kidney (L of blood cleared of urea x d(-1) x kg BW(-1)) was greater for pigs and rats than for herbivores (cattle, sheep, goats, horses). A model was developed to estimate parameters of N utilization. Driving variables for the model included blood urea N concentration (mg/100 mL), BW (kg), milk production rate (kg/d), and ADG (kg/d), and response variables included urinary N excretion rate (g/d), fecal N excretion rate (g/d), rate of N intake (g/d), and N utilization efficiency (N in milk and gain per unit of N intake). Prediction errors varied widely depending on the variable and species of animal, with most of the variation attributed to study differences. Blood urea N concentration (mg/100 mL) can be used to predict relative differences in urinary N excretion rate (g/d) for animals of a similar type and stage of production within a study, but is less reliable across animal types or studies. Blood urea N concentration (mg/100 mL) can be further integrated with estimates of N digestibility (g/g) and N retention (g/d) to predict fecal N (g/d), N intake (g/d), and N utilization efficiency (grams of N in milk and meat per gram of N intake). Target values of blood urea N concentration (mg/100 mL) can be backcalculated from required dietary N (g/d) and expected protein digestibility. Blood urea N can be used in various animal species to quantify N utilization and excretion rates.

The effects of anAspergillus oryzaeextract containing alpha-amylase activity on ruminal fermentation and milk production in lactating Holstein cows

The effects of anAspergillus oryzaeextract containing alpha-amylase activity (Amaize™, Alltech Inc., Nicholasville, KY) were examinedin vivoandin vitro. A lactating cow study employed 20 intact and four ruminally fistulated Holstein cows in a replicated 4 × 4 Latin-square design to examine the effects of four concentrations of dietary Amaize™ extract on milk production and composition, ruminal fermentation and serum metabolite concentrations. The treatment diets contained 0, 240, 480 or 720 alpha-amylase dextrinizing units (DU) per kg of total mixed ration (TMR) (dry-matter basis). The supplemental alpha-amylase increased the yields of milk (P= 0·02), fat (P= 0·02) and protein (P= 0·06) quadratically. The maximum milk yield was obtained when 240 DU per kg of TMR were offered. Ruminalin situstarch disappearance was not affected by alpha-amylase supplementation in lactating cows or ruminally cannulated steers. Supplemental alpha-amylase extract reduced the molar proportion of propionate in the rumen of steers (P= 0·08) and lactating cows (P= 0·04), and in rumen-simulating cultures (P= 0·04). The supplement also increased the molar proportions of acetate (P= 0·06) and butyrate (P= 0·05), and the serum beta-hydroxybutyrate (P= 0·01) and non-esterified fatty acid (P= 0·03) concentrations in lactating cows. The improvements in milk production appear to be a consequence of the effects of alpha-amylase on ruminal fermentation and the potential changes in nutrient metabolism that result from them. We conclude that supplemental alpha-amylase may be given to modify ruminal fermentation and improve milk and component yield in lactating Holstein cattle.

Integration of Ruminal Metabolism in Dairy Cattle

An important objective is to identify nutrients or dietary factors that are most critical for advancing our knowledge of, and improving our ability to predict, milk protein production. The Dairy NRC (2001) model is sensitive to prediction of microbial protein synthesis, which is among the most important component of models integrating requirement and corresponding supply of metabolizable protein or amino acids. There are a variety of important considerations when assessing appropriate use of microbial marker methodology. Statistical formulas and examples are included to document and explain limitations in using a calibration equation from a source publication to predict duodenal flow of purine bases from measured urinary purine derivatives in a future study, and an improved approach was derived. Sources of specific carbohydrate rumen-degraded protein components probably explain microbial interactions and differences among studies. Changes in microbial populations might explain the variation in ruminal outflow of biohydrogenation intermediates that modify milk fat secretion. Finally, microbial protein synthesis can be better integrated with the production of volatile fatty acids, which do not necessarily reflect volatile fatty acid molar proportions in the rumen. The gut and splanchnic tissues metabolize varying amounts of volatile fatty acids, and propionate has important hormonal responses influencing milk protein percentage. Integration of ruminal metabolism with that in the mammary and peripheral tissues can be improved to increase the efficiency of conversion of dietary nutrients into milk components for more efficient milk production with decreased environmental impact.

Milk from Forage as Affected by Carbohydrate Source and Degradability with Alfalfa Silage-Based Diets

Milk from forage (MF) is an estimation of the milk produced solely from forage intake. It is calculated by subtracting milk production theoretically allowed by concentrates from total milk production, assuming that maintenance requirements are covered by the forage portion of the diet. Eight multiparous Holstein cows in early lactation were used in a replicated 4 x 4 Latin square design to evaluate the impact on MF of different sources of carbohydrate with forage that was high in RDP. Diets were alfalfa-based total mixed rations that were formulated to provide similar concentrations of NEL and CP while differing in rumen degradability of concentrate carbohydrates. Treatments were 1) cracked corn (control), 2) ground corn (GC), 3) GC plus wheat starch (GC+S), and 4) GC plus dried whey permeate (GC+W). The GC and the GC+S treatments increased MF as calculated on a protein basis (14.8 vs. 10.5 kg) and increased average MF production (8.6 vs. 5.5 kg) compared with the control. Protein of forage was used more efficiently with GC and with GC+S, as shown by the lower differences between allowable MF, which estimates the potential for milk production from forage, and MF on a protein basis for these 2 treatments when compared with the control. Compared with the control, DMI increased with GC and GC+S; GC+W yielded the highest DMI. Milk production with GC+W (35.8 kg/d) was lower than with GC and GC+S (37.5 kg/d) but was higher than the control (34.0 kg/d). Milk fat concentration was higher with GC+W and lower with GC+S; GC and the control had intermediate values. Milk urea was higher with the control diet compared with the other 3 treatments. Results emphasize the advantage of using concentrates of higher degradability in the rumen to improve MF and milk production when feeding silage with high rumen-degradable protein.

Development of a System to Predict Feed Protein Flow to the Small Intestine of Cattle

A data set constructed from research trials published between 1979 and 1998 was used to derive equations to adjust published tabular values for the rumen-undegradable protein (RUP) content of feeds to better predict the passage of nonammonia nonmicrobial N (NANMN) to the small intestine of lactating dairy cows. Both linear and nonlinear forms of equations were considered for making adjustments. Iterative processes were used to estimate equation parameters. A logistic equation was developed and considered to be the most optimal for adjustment of published tabular RUP contents of feeds. The equation is a function of dietary dry matter intake (DMI) and includes terms for tabular RUP and nonprotein N contents of individual feeds. The equation has a standard error of prediction of 69.29 g of NANMN/ d per cow and a root mean square prediction error of 104.63 g of NANMN/d per cow. Independent evaluation of the equation indicated that the concept of variable RUP content for feeds based on DMI is correct. Further refinements may be needed as other data become available to quantify the effects of additional factors on the RUP value of feeds.

Lactation Performance of Holstein Cows Fed Fescue, Orchardgrass, or Alfalfa Silage

Perennial grasses are increasingly being used as an integral part of nutrient management plans, but fescue (Festuca arundinacea Schreb.) is often overlooked because of perceived intake problems. A 30-d study was conducted to evaluate the lactation performance of cows fed a fescue silage-based total mixed ration (TMR) compared with orchardgrass (Dactylis glomerata L.) and alfalfa (Medicago sativa L.) silage-based TMR, when forages are harvested at recommended neutral detergent fiber (NDF) levels. Holstein cows (body weight [BW] = 627 +/- 66.0 kg, milk yield = 40.9 +/- 6.93 kg/d, parity = 2.6 +/- 1.44, days in milk = 152 +/- 24.5) were randomly assigned to treatment. Statistical design was a randomized complete block with 10 cows per treatment. The 5 treatments consisted of TMR using first-cutting alfalfa, and first- and second-cutting orchardgrass and tall fescue silage. Diets were formulated to provide 0.95% of BW as forage NDF and contained approximately 18% CP and 1.6 mcal/kg. This resulted in diets of about 30% NDF; for a 612-kg cow, approximately 5.8 kg/d of forage NDF was fed. Second-cutting, grass-based TMR had lower intake than alfalfa and first-cutting forage TMR. Cows consuming second-cutting orchardgrass had lower milk production than did cows consuming other forage TMR. Cows fed fescue TMR had higher milk production than those fed orchardgrass. Indigestible residues were higher, and NDF digestibilities were lower, in second-cutting forages vs. first-cutting forages, likely contributing to the differences observed in intake and resulting differences in milk production. Dairy cows consumed the first-cutting fescue TMR readily and performed as well as those on alfalfa or first-cutting, orchardgrass-based TMR in terms of lactation performance, but fescue and orchardgrass rations will require more concentrate in the ration than alfalfa.

Influence of Dietary Nonfiber Carbohydrate Concentration and Supplementation of Sucrose on Lactation Performance of Cows Fed Fescue Silage

There is interest in knowing if the source of nonfibrous carbohydrates (NFC) influences milk production and composition. Our objective was to determine the effects of source (starch or sugar) and level of NFC in the diet on these parameters. A 4 x 4 Latin square replicated five times using early-lactation (56 +/- 9 DIM) Holstein cows was used; cows were offered one of two levels of NFC and either no added sucrose or sucrose substituting for 10% of the corn. Diets were balanced to meet National Research Council requirements for total protein, energy, and minerals. Tall fescue silage was included at one of two levels (0.95 or 1.25% of BW as forage NDF), resulting in diets with 40 and 30% NFC. The remaining ingredients consisted of high-moisture corn, soybean meal, SoyPlus, minerals, and vitamins. Megalac (0.45 kg) was used in the low NFC diets. High NFC diets were lower (P < 0.01) in neutral detergent fiber (NDF; 31.5%) and crude protein (CP; 19.6%) than the low NFC diet (35.8% NDF and 21.0% CP). Sucrose containing diets were somewhat lower (P < 0.01) in NDF (33.1%) than the no sucrose added diets (34.3%), but diets did not differ in CP%. Cows offered the high NFC level produced more milk (39.6 kg/d; P < 0.05) than those offered the low level (38.3 kg/d), primarily due to higher dry matter intake (P < 0.05). Cows consuming the high NFC diet also had lower (P < 0.05) milk fat (3.25%) and milk urea nitrogen (MUN; 13.7 mg/dl), and higher (P < 0.05) milk protein (2.58%) and milk lactose (4.81%) concentrations than cows offered the low NFC level (3.46% milk fat, 17.5 mg/dl MUN, 2.51% milk protein, and 4.74% milk lactose). Fat yield was higher (P < 0.05) for cows fed low NFC diets than cows fed high NFC diets, whereas protein and fat yield were lower (P < 0.05) for cows fed low NFC diets than those fed high NFC diets. The NFC source did not influence dry matter intake or milk production or milk component yield (P > 0.05). Milk lactose (4.79%) and MUN (16.0 mg/dl) concentrations were higher (P < 0.05) for cows offered sucrose as a portion of the NFC compared with those not offered sucrose (4.76% milk lactose and 15.2 mg/dl MUN). Results suggest that cows fed sucrose may utilize diet nitrogen less efficiently than those not fed sucrose, when sucrose is replacing a portion of the high-moisture corn in the diet.

The effect of corn silage particle size and cottonseed hulls on cows in early lactation

The objective of this study was to evaluate the effects of reducing forage particle length (FPL) and the inclusion of cottonseed hulls (CSH) on intake, digestibility, chewing activity, and milk production of cows in early lactation. Sixteen multiparous cows averaging 17 +/- 3 d in milk and 677 +/- 58 kg BW were assigned to one of four 4 x 4 Latin squares. One square contained ruminally cannulated cows to evaluate effects of treatment on rumen fermentation and function. During each of the 23-d periods, cows were offered one of four total mixed rations that differed in particle length (long or short corn silage) and CSH inclusion rate (0 or 8% DM). Dietary treatments were: long no CSH (LGNH), long with CSH (LGH), short no CSH (SHNH), and short with CSH (SHH). Total physically effective NDF content, measured as percentage of NDF greater than 1.18 mm, was similar across diets, but mean particle length decreased with reducing FPL and inclusion of CSH. Dry matter intake was not significantly affected by FPL but was significantly increased with the inclusion of CSH. Decreasing FPL and the inclusion of CSH significantly increased neutral detergent fiber intake. Total chewing activity expressed as minutes per day was unaffected by FPL and the inclusion of CSH. Both eating and ruminating efficiency expressed as minutes per kilogram of neutral detergent fiber intake increased with increasing FPL and decreased with the inclusion of CSH. Milk production did not differ across treatments, but the inclusion of CSH significantly increased percent and yield of milk protein. Reducing FPL tended to reduce percentage milk fat but not yield. Mean ruminal pH was not affected by FPL but was highest on diets containing CSH, even though no treatment effects were observed on total VFA, acetate, or propionate concentration. These resuits indicate that corn silage FPL is a poor predictor of total chewing time and rumen pH but is useful in understanding factors affecting feeding behavior. In addition, the inclusion of CSH, resulted in increased rumination and mean rumen pH even though effects on VFA concentration were not observed.

The effect of reducing alfalfa haylage particle size on cows in early lactation

The objective of this experiment was to evaluate effects of reducing forage particle size on cows in early lactation based on measurements of the Penn State Particle Separator (PSPS). Eight cannulated, multiparous cows averaging 19 +/- 4 d in milk and 642 +/- 45 kg BW were assigned to one of two 4 x 4 Latin Squares. During each of the 23-d periods, animals were offered one of four diets, which were chemically identical but included alfalfa haylage of different particle size; short (SH), mostly short (MSH), mostly long (MLG), and long (LG). Physically effective neutral detergent fiber (peNDF) was determined by measuring the amount of neutral detergent fiber retained on a 1.18 mm screen and was similar across diets (25.7, 26.2, 26.4, 26.7%) but the amount of particles >19.0 mm significantly decreased with decreasing particle size. Reducing haylage particle size increased dry matter intake linearly (23.3, 22.0, 20.9, 20.8 kg for SH, MSH, MLG, LG, respectively). Milk production and percentage fat did not differ across treatments averaging 35.5 +/- 0.68 kg milk and 3.32 +/- 0.67% fat, while a quadratic effect was observed for percent milk protein, with lowest values being observed for LG. A quadratic effect was observed for mean rumen pH (6.04, 6.15, 6.13, 6.09), while A:P ratio decreased linearly (2.75, 2.86, 2.88, 2.92) with decreasing particle size. Total time ruminating increased quadratically (467, 498, 486, 468 min/d), while time eating decreased linearly (262, 253, 298, 287 min/d) with decreasing particle size. Both eating and ruminating per unit of neutral detergent fiber intake decreased with reducing particle size (35.8, 36.7, 44.9, 45.6 min/kg; 19.9, 23.6, 23.5, 23.5 min/kg). Although chewing activity was closely related to forage particle size, effects on rumen pH were small, indicating factors other than particle size are critical in regulating pH when ration neutral detergent fiber met recommended levels. Feeding alfalfa haylage based rations of reduced particle size resulted in animals consuming more feed but did not affect milk production.

Supplemental carbohydrate sources for lactating dairy cows on pasture

Two experiments were conducted to evaluate steam-flaked corn and nonforage fiber sources as supplemental carbohydrates for lactating dairy cows on pasture. Cows were allotted to a new paddock of an orchardgrass (Dactylis glomerata L.) pasture twice daily in one group in both trials. In experiment 1, 28 Holstein cows, averaging 216 d in milk, were randomly assigned to either a cracked-corn (CC) or a steam-flaked (SFC) supplement in a split plot design. The supplement contained 66.7% of corn and a protein/mineral pellet. In experiment 2, 28 Holstein cows, averaging 182 d in milk, were randomly assigned to either a ground corn (GC) or a nonforage fiber (NFF)-based supplemented in a single reversal design. The GC supplement contained 85% ground corn plus protein, mineral, and vitamins. The NFF supplement contained 35% ground corn, 18% beet pulp, 18% soyhulls, 8% wheat middlings plus protein, mineral, and vitamins. In both experiments, cows were fed the grain supplement twice daily after each milking at 1 kg/4 kg milk. In experiment 1, milk production (24.3 kg/d) and composition did not differ between treatments; however, plasma and milk urea N were lower with the SFC supplement. In experiment 2, milk production (27.5 kg/d) was not affected by treatments, which may be related to the medium quality of pasture grazed. The GC supplement tended to reduce plasma and milk urea N and increased milk protein percentage (3.23 vs. 3.19%). Pasture dry matter intake, measured using Cr2O3, did not differ between treatments in either experiment 1 (15.1 kg/d) or experiment 2 (12.2 kg/d). Milk production did not differ when mid-late lactation cows on pasture were supplemented with SFC or NFF instead of dry corn.

Ruminal fermentation and nutrient digestion by dairy cows fed varying amounts of soyhulls as a replacement for corn grain

Five multiparous Holstein cows cannulated in the rumen and duodenum that averaged 63 d in milk were used in a 5 x 5 Latin square design with 14-d periods to evaluate the incremental substitution of soyhulls for corn in the diet. Diets contained 23% alfalfa silage, 23% corn silage, and 54% concentrate on a dry matter (DM) basis. Pelleted soyhulls replaced corn in the concentrate to supply 0, 10, 20, 30, or 40% of the dietary DM. The intakes of DM and organic matter were unaffected by treatments. Intakes of acid detergent fiber and neutral detergent fiber increased linearly, but the intake of nonstructural carbohydrates decreased linearly as soyhulls increased from 0 to 40% of dietary DM. The amount of acid detergent fiber and neutral detergent fiber digested was increased whereas the amount of nonstructural carbohydrate digested was decreased in the rumen, in the lower digestive tract, and in the total digestive tract as soyhulls replaced corn in the diet. Passage to the duodenum of nonammonia N, microbial N, nonammonia nonmicrobial N, total essential amino acids, total nonessential amino acids, and total amino acids were not affected by treatments. Yield of milk (29.5 kg/d) was not affected by treatments in this experiment. In a companion experiment, cows fed the 40% SH diet produced 1.2 kg/day per cow less (P < 0.07) milk than cows fed the control diet which is similar to the 1.3 kg/day per cow less milk produced by cows fed the same 40% SH diet in this experiment. Differences in the source of energy (fiber vs. nonstructural carbohydrates), in the amount of fiber and nonstructural carbohydrates digested, and in the site of digestion in the gastrointestinal tract may cause a shortage of the source and/or amount of energy that is required for maximum milk production in high producing cows when more than 30% of the dietary DM that is supplied as corn is replaced with soyhullss.

Modelling Mammary Metabolism in the Dairy Cow to Predict Milk Constituent Yield, with Emphasis on Amino Acid Metabolism and Milk Protein Production: Model Evaluation

A model of mammary metabolism has been constructed and parameterized, with milk protein synthesis represented as a function of five essential amino acids (EAA) (Hanigan et al., 2001). Herein the model is evaluated using both the data used to construct the model (reference data) and an independent data set (literature data), and sensitivity to inputs and parameter estimates is assessed. The model predicted metabolite removal well for the reference data with exceptions for glutamate, glucose, and acetate. However, predictions of milk protein synthesis exhibited significant mean positive bias, which apparently was associated with the representation of milk protein synthesis. Adjustment of model parameters removed the mean bias, however, prediction accuracy was still inadequate. Simulation of the single reference experiment containing all critical inputs resulted in predictions of milk protein output that explained 53% of the observed variation, suggesting that the limited accuracy of the model when applied to the entire reference data set was due to assumptions regarding missing inputs. Mammary removal of glutamate, isoleucine, lysine, phenylalanine, tyrosine, valine, glycerol, beta -hydroxybutyrate (BHBA), and acetate were predicted less accurately when simulations of the independent data set were conducted. Twenty-five percent of the observed variation in milk protein yields for the independent data set was explained by the model. Refitting parameters for removal of isoleucine, lysine, phenylalanine, tyrosine, valine, glycerol, BHBA, and acetate raised the variation explained to 43%. Sensitivity analysis indicated that milk protein synthesis was responsive to only the five EAA used in its determination, with sensitivity to any single EAA falling to zero as supply of the EAA exceeded protein synthetic needs. Similarly, milk protein synthesis was readily affected by parameters associated with removal and metabolism of the five EAA. Milk lactose was found to be sensitive to glucose input as well as to similar parameters and inputs as milk protein. It is concluded that representation of the milk protein synthesis process as a function of a single limiting EAA may not be adequate and might be better represented by simultaneous consideration of multiple EAA. Additional work on the description of energy metabolism is also suggested.

The relationship of milk urea nitrogen to urine nitrogen excretion in Holstein and Jersey cows

The objectives of this study were to assess the relationship between urinary nitrogen excretion (UN, g/d) and milk urea nitrogen concentration (MUN, mg/dl) and whether the types of carbohydrates fed interacts with the dietary CP and the breed (size) of cows to affect this relationship. Eight multiparous cows (four Holstein and four Jersey) were fed four different diets in a 2 x 2 factorial arrangement of levels of crude protein (13 and 17%) and levels of neutral detergent fiber (30 and 40%). The experimental design was a split plot Latin square with breeds forming the main plots and diets forming the subplots. Experimental periods were 3 wk in length, with d 1 to 14 used for adjustment and d 15 to 19 used for a total collection of urine and feces. Crude protein concentrations had a significant effect on milk, milk fat and protein production, plasma urea N, MUN, and on N balance measurements (N intake, fecal and urinary N excretion, milk N production, N retention, apparent N digestibility, and N efficiency). Neutral detergent fiber levels had no effect on any production parameters or N balance measurements. The relationship between urinary N and MUN was linear over the range of MUN values observed and different for the two breeds. The breed effect on the UN-MUN relationship was no longer significant (P = 0.63) when body weight (BW) was included in the model. The optimal allometric coefficient for BW was 0.96 and was not different from 1.0. Therefore, the following equation is proposed to predict UN excretion based on MUN and BW: UN (g/d) = 0.0259 (+/- 0.0006) BW (kg) x MUN (mg/dl).

Strategies for increasing energy density of dry cow diets

The objective of this trial was to compare the effects of increasing dietary energy density from 1.51 to 1.65 Mcal/kg of dry matter (DM) by replacing forage with concentrate or by further increasing concentrate via the substitution of corn silage and alfalfa silage by a mixture of straw, starch, and soybean meal. Our hypothesis was that the latter diet would be more glucogenic while increasing rumen fill and be potentially desirable for transition cows. Nine far-off dry cows (greater than 3 wk before parturition at the end of the trial) were fed three diets: low energy diet, [LE, 1.51 Mcal/kg of DM, 14.0% crude protein (CP) and 35% nonfiber carbohydrates (NFC)], high energy diet, (HE, 1.65 Mcal/kg of DM, 13.9% CP and 39.5% NFC) and high energy diet, where a portion of alfalfa and corn silage was replaced by straw, soybean meal, and cornstarch (HES, 1.65 Mcal/kg of DM, 13.5% CP and 40.5% NFC). The experiment was a replicated 3 x 3 Latin square design with 21-d periods. Six cows from two squares were used to examine kinetics of DM disappearance from nylon bags suspended in the rumen. Two contrasts of interest were: LE versus HE, HES (effects of energy density) and HE versus HES (method of increasing energy density). Increasing energy density increased the potentially degradable (B) and decreased the undergradable (C) DM fractions of the diets. Because HES had greater B and a faster rate of degradation of fraction B (k), effective rumen degradable DM (ERDDM) was higher in HES compared to HE. Cows fed high energy diets had greater DM intake. No differences in DM intake were observed between HE and HES. Rumen volume or DM pool sizes were not affected by treatment. High energy diets increased total ruminal fluid volatile fatty acid concentration compared with LE. Propionate concentration was higher in cows fed high energy diets compared with cows fed LE. The partial replacement of alfalfa and corn silage by straw, soybean meal, and cornstarch further increased propionate concentration. The greatest increase in serum insulin concentration following feeding was observed in cows fed HE. Cows consuming high energy diets had lower plasma nonesterified fatty acids (NEFA) before and after feeding. The HES diet was less effective in decreasing plasma NEFA concentration after feeding compared to HE. In conclusion, increasing diet energy density of far-off dry cows positively affected DMI, ruminal propionate, serum insulin, and plasma NEFA. Increasing energy density with a blend of feeds that represent extremes in rates of carbohydrate fermentation may be a strategy to provide greater amounts of glucogenic precursors. Applicability of this strategy should be examined in transition cows.

Effects of NutriDense and waxy corn hybrids on the rumen fermentation, digestibility and lactational performance of dairy cows

The objectives of this study were to determine the effects of NutriDense and waxy corn hybrids as silage and grain sources on milk yield, milk composition, digestibility of dietary components, and rumen characteristics. Six multiparous (intact) and six primiparous (ruminally cannulated) Holstein cows were assigned at 72 to 90 d of lactation to a 3 x 6 Latin rectangle design experiment to treatment of: 1) control diet, 2) NutriDense corn diet, and 3) waxy corn diet. Diets consisted of 10.9% alfalfa silage, 32.8% corn silage, 27.9% cracked corn grain, and 28.4% other ingredients (DM basis). Milk, FCM, and milk fat and protein yields were higher for cows fed the waxy diet than those fed the control diet. Milk protein percentage tended to be higher for cows fed the control and waxy diets than those fed the NutriDense diet. Dry matter intake tended to be higher for cows fed the waxy diet than the NutriDense diet. Apparent DM, OM, CP, ADF, NDF, and gross energy digestibilities were similar among dietary treatments, while apparent starch digestibility was higher for the waxy corn than for the NutriDense corn. Rumen NH3-N concentration was higher for cows fed the NutriDense diet than for those fed the control and waxy diets. The proportion of ruminal propionate was higher for the waxy diet than the control diet. NutriDense and waxy corn hybrids can be effective substitutes for conventional yellow dent corn hybrids in lactating dairy cow rations.

Improving energy supply to late gestation and early postpartum dairy cows

Sixty-five multiparous Holstein cows were used to test the effects of feeding diets of varied ruminal carbohydrate availability during the transition period on dry matter intake, blood metabolites, and lactational performance. Cows received total mixed rations containing either cracked corn or steam-flaked corn beginning 28 d prior to expected calving date. At parturition, cows were assigned to a postpartum total mixed ration that contained either cracked corn or steam-flacked corn. Diets were fed until 63 d in milk. No treatment effects on prepartum or postpartum dry matter intake, body weight, and body condition score were observed. Cows fed steam-flaked corn had lower blood urea N concentrations during the prepartum period and lower plasma nonesterified fatty acid concentrations during the prepartum and postpartum periods. Cows fed steam-flaked corn postpartum produced 2.3 kg/d more milk than cows fed cracked corn during the first 63 d in milk. Fat corrected milk showed no treatment effect. Seven cows were used to evaluate treatment effects on ruminal fermentation and digesta kinetics. Prepartum and postpartum treatments had minimal effects on ruminal fermentation. Feeding steam-flaked corn prepartum decreased apparent fiber digestibility and ruminal NH3 N. Feeding steam-flaked corn postpartum decreased the acetate to propionate ratio. Prepartum and postpartum treatments did not affect digesta kinetics. An increase in ruminal carbohydrate availability during the postpartum period enhanced milk production, but had variable results on ruminal fermentation.

Effects of extrusion of grain and feeding frequency on rumen fermentation, nutrient digestibility, and milk yield and composition in dairy cows

The effect of corn extrusion and feeding frequency on ruminal and postruminal digestibility and milk yield was studied in cows fed a high concentrate diet. Four Israeli Holstein cows fitted with rumen and abomasal cannulas were used. The experiment was arranged as a 2 x 2 factorial design, with two diets and two feeding frequencies (two or four meals per day). One diet contained 40% ground corn. In the second diet, half of the ground corn was replaced with extruded corn. Feeding cows the extruded versus ground corn diet decreased ruminal ammonia N and plasma urea N concentrations, increased postruminal digestibility of nonstructural carbohydrates, reduced dry matter intake, decreased yield of milk and milk components, and increased efficiency of milk energy and milk protein synthesis. The inclusion of extruded corn in the diet did not affect ruminal volatile fatty acid. Increasing the feeding frequency reduced the diurnal variation in ruminal pH, ruminal ammonia, and plasma urea, and increased dry matter intake--considerably more in the cows fed ground versus extruded corn--and improved postruminal organic matter, nonstructural carbohydrate, and crude protein digestibility. Total tract digestibility of organic matter and crude protein and milk yield and composition were also increased when cows were fed four versus two meals. Concurrent with the feeding frequency and grain processing effect, an increase in rumen-undegradable protein flow was related to increased digestion of nonstructural carbohydrate postruminally (r = 0.54). We concluded that for cows fed high-starch diets more frequent meals are useful for improving postruminal digestibility and milk yield and composition.

Varying degradation rates of total nonstructural carbohydrates: effects on nutrient uptake and utilization by the mammary gland in high producing Holstein cows

Six ruminally cannulated Holstein cows at 56 to 77 d of lactation were fed three total mixed rations that varied in ruminal degradation rates of total nonstructural carbohydrates (6.04, 6.98, and 7.94%/h). The design was a 3 x 6 Latin square with 21-d experimental periods. Cows were catheterized in the jugular vein and in one of the caudal superficial epigastric veins. Increases in the ruminal degradation rate of total nonstructural carbohydrates 1) elevated mammary blood flow and blood concentrations of nonessential amino acids; 2) decreased arteriovenous differences and extraction rates of essential and most nonessential amino acids, but not of Gln and Glu (analyzed together) and glucose; 3) increased mammary uptake of Gln, Glu, and glucose; milk protein concentrations of Glu, Pro, and Asp; and total nonessential amino acids; and 4) did not alter uptake to output ratios of amino acids in the mammary gland, however, of the nonessential amino acids, only the uptake to output ratios for Glu and Gln increased (19%). Glucose and amino acid arteriovenous differences were not strongly correlated with their arterial concentrations. Increases in the ruminal degradation rate of total nonstructural carbohydrates increased intestinal digestibilities of total nonstructural carbohydrates and protein and increased uptake of energy substrates by the mammary gland, resulting in a 13% improvement in the utilization of nonessential amino acids for milk protein synthesis and in higher milk production and milk protein yields.