Extent of methionine limitation in peak-, early-, and mid-lactation dairy cows.

Five multiparous, ruminally and duodenally cannulated Holstein cows were assigned to 5 x 5 Latin squares at wk 2 (experiment 1), wk 11 to 13 (experiment 2), and wk 17 to 19 postpartum (experiment 3) to determine extent of Met limitation. Treatments were duodenally infused and consisted of 10 g/d of l-Lys plus 0, 3.5, 7.0, 10.5, or 16.0 g/d of dl-Met in experiments 1 and 2 and 8 g/d of l-Lys plus 0, 5, 10, 15, or 20 g/d of dl-Met in experiment 3. Calculated Lys contributions to total AA (TAA) in duodenal digesta for control treatments were 8.6, 7.5, and 9.0% for experiments 1, 2, and 3, respectively. Methionine contributions to TAA for the 5 infusion treatments were 1.9, 2.1, 2.2, 2.4, and 2.7% for experiment 1; 2.1, 2.3, 2.4, 2.5, and 2.7% for experiment 2; and 1.8, 2.0, 2.2, 2.4, and 2.5% for experiment 3, respectively. Milk protein yield increased linearly in experiments 1 and 2, indicating that Met contribution to TAA in duodenal digesta for maximal milk protein synthesis exceeded 2.7 for early-lactation cows. In experiment 2, a quadratic relationship was found between level of infused Met and milk protein content, with the response reaching a plateau when 12.2 g of Met was infused, corresponding with a Met contribution to TAA in duodenal digesta of 2.4%. In experiment 3, milk protein content increased quadratically, but milk yield declined linearly with increasing levels of infused Met; hence, milk protein yield was unaffected by treatment. The calculated plateau point of the milk protein content response curve was determined to be 12.4 g of infused Met, which corresponds to a Met contribution to TAA in duodenal digesta of 2.3%. Experiment 3 results indicate that the required level of Met in duodenal digesta for maximizing milk protein yield is lower than that required for maximizing milk protein content.

Evaluation of the passage rate equations in the 2001 Dairy NRC model.

Dairy ration formulation to meet protein and amino acid requirements with the National Research Council Nutrient Requirements of Dairy Cattle (NRC, 2001) model depends on accuracy of predicting feed passage rates out of the rumen. The NRC (2001) passage rate (Kp) equations were evaluated for validity and sensitivity to input variables in predicting supplies of rumen degraded protein, rumen undegraded protein, and metabolizable protein. The database used in the development of the 3 Kp equations (for dry forage, wet forage, and concentrate) was used to independently derive the 3 equations using a meta-analysis technique. To extract quantitative relationships between statistically significant input variables and rate of passage, a random coefficients model that used each study effect as a random variable was used. The database was comprised of studies that only used rare earth markers. Outliers were identified by acceptance criteria defined a priori or the difference in fit statistic (DFFITS) value; 319, 63, and 139 treatment means were used to develop the Kp equations for dry forage, wet forage, and concentrate, respectively. We found that the sign of the regression coefficient for concentrate content in diet dry matter in the equation for Kp dry forage was inverted; it should be positive. A sensitivity analysis was conducted with a spreadsheet version of the NRC (2001) model developed for this study, using the Monte Carlo technique. The sensitivity analysis indicated that all Kp predictions were the most sensitive to variation in DM intake, and thus accurate measurement of DM intake is the most important factor in predicting Kp. Predictions for protein supply (rumen degraded protein, rumen undegraded protein, and metabolizable protein) were sensitive to variability in amount of feed crude protein (CP, %DM), digestion rate (Kd) of the B fraction of feed CP (%/h), and the Kp for concentrate (%/h), due to the high proportion of dietary CP in lactating dairy rations coming from concentrates. The sensitivity analysis indicated that accurate determinations of DMI, the Kd of the B fraction of feed CP, and feed CP are the most important variables needed to predict MP supply in lactating dairy cows with the NRC (2001) model. We conclude that the empirical Kp equations in the model are suitable for predicting passage rate in lactating dairy cows. More accurate predictions of Kp will require the development of a more mechanistic model that accounts for more of the biologically important variables (e.g., physical property of particles, liquid flow, and timely variation of intake) affecting passage rate.

Improving intestinal amino acid supply of pre- and postpartum dairy cows with rumen-protected methionine and lysine.

Eighty-four Holstein cows were assigned to a randomized block experiment to determine effects of supplementing pre- and postpartum diets containing highLys protein supplements with rumen-protected Met and Lys. Before parturition, cows received a basal diet with 1) no rumen-protected amino acids (AA), 2) 10.5 g/d of Met from rumen-protected Met, or 3) 10.2 g/d of Met and 16.0 g/d of Lys from rumen-protected Met plus Lys. After parturition, cows continued to receive AA treatments but switched to diets balanced for 16.0 or 18.5% crude protein (CP). Diets were corn-based; supplemental protein was provided by soybean products and blood meal. Cows received treatments through d 105 of lactation. Compared with basal and Met-supplemented diets, Met + Lys supplementation increased yield of energy-corrected milk, fat, and protein, and tended to increase production of 3.5% fat-corrected milk. Significant CP x AA interactions were observed only for milk protein and fat content. Supplementation of the 16% CP diet with Met and Met + Lys had no effect on milk true protein and fat content. However, Met and Met + Lys supplementation of the 18.5% CP diet increased milk protein content by 0.21 and 0.14 percentage units, respectively, and Met supplementation increased fat content by 0.26 percentage units. Results of this study indicate that early-lactation cows fed corn-based diets are responsive to increased intestinal supplies of Lys and Met and that the responses depend on dietary CP concentration, supply of metabolizable protein, and intestinal digestibility of the rumen-undegradable fraction of supplemental proteins.

Effect of yeast culture in the diets of early lactation dairy cows on ruminal fermentation and passage of nitrogen fractions and amino acids to the small intestine.

Eight early lactation, primiparous Holstein cows were fitted with ruminal and duodenal cannulas. The cows were used in a replicated 4 x 4 Latin square design to test the effects of yeast culture (0 vs. 10 g/ d) and dietary crude protein (CP) (16.1 vs. 18.8% of dry matter) in 44% forage diets. Dietary CP differed primarily in ruminally degradable CP (9.1 vs. 11.4% of dry matter). Dry matter intake tended to increase as amount of yeast culture increased. However, yeast culture had no effect on ruminal pH, concentrations of NH3 and volatile fatty acids in ruminal fluid, or ruminal digestibility. Yeast culture increased the ruminal concentration of isobutyrate in cows fed the low CP diet and decreased the concentration of isobutyrate in cows fed the high CP diet. The higher CP diets increased microbial N passage to the duodenum and had no effect on passage of nonmicrobial nonammonia N. Flows to the duodenum of nonmicrobial nonammonia N tended to be higher for cows fed yeast culture. Flows of essential amino acids to the duodenum and the essential amino acid profiles of duodenal digesta and of mixed ruminal bacteria were not altered by yeast culture. Yields of fat and 4% fat-corrected milk were increased by yeast culture supplementation of the low CP diet. Similar tendencies were noted for yields of milk and milk protein.

Whole milk and oral rehydration solution for calves with diarrhea of spontaneous origin.

Forty-two calves (mean 10 d of age) that spontaneously contracted diarrhea were used to test the therapeutic value of an oral rehydration solution with or without whole milk. Therapy began on the first feeding after a fecal score was > 2 (five-point scale). Amounts (percentages of BW daily) of milk and oral rehydration solution on d 1 and 2, 3 and 4, 5 and 6, and 7 for treatments 1, 2, and 3 were 1) 0 and 10, 5 and 5, 7.5 and 2.5, 10 and 0% (in two feedings); 2) 2.5 and 10, 5 and 7.5, 7.5 and 5, 10 and 0% (in two feedings); 3) 10 and 10, 10 and 5, 10 and 2.5, 10 and 0% (in three feedings). Oral rehydration solution was fed 15 min after milk. Fecal score, rectal temperature, packed cell volume of whole blood, concentrations of glucose and electrolytes in serum, and strong ion difference of serum were unaffected by treatments. Calves given treatment 3 gained BW throughout the experiment, whereas those given treatments 1 and 2 lost BW during the first 3 d of therapy. Fecal cultures indicated that 70% of calves were infected with Cryptosporidium on d 1 of therapy. No mortality occurred. Whole milk and oral rehydration solution fed to calves did not adversely affect calves or prolong or worsen diarrhea but promoted gain of BW.