Twelve multiparous Holstein cows averaging 57 d (36 to 77 d) postpartum at the start of the experiment were utilized in a replicated 4 × 4 Latin square design. Dietary protein supplements were 1) soybean meal, 2) soybean meal plus ruminally protected Lys and Met, 3) corn distillers grains, and 4) corn distillers grains plus ruminally protected Lys and Met. Dry matter intakes were lower for cows fed diets containing soybean meal than for cows fed diets containing corn distillers grains. Milk yield increased with the corn distillers grains (34.3, 34.0, 35.3, and 36.7 kg/d for cows fed diets 1 through 4, respectively), especially when supplemented with ruminally protected Lys and Met. Milk protein yield and percentage were increased by amino acid supplementation. Milk fat yield and percentage were unaffected by diet. The only milk protein fraction affected was nonprotein N, which was lower in the milk of cows fed corn distillers grains. Lysine, Met, and Phe were indicated as the most limiting amino acids for all diets when using amino acid extraction efficiency and transfer efficiency to indicate limiting amino acids. When corn distillers grains were supplemented with ruminally protected Lys and Met, milk yield and milk protein yield and percentage increased because the diet containing corn distillers grains was probably deficient in Lys.
Bibliographical noteFunding Information:
Appreciation is extended to the South Dakota Corn Utilization Council for partial financial support of this research, to Rhône-Poulenc for donating the Smartamine ML used in this research, to Valley Queen Cheese Factory (Milbank, SD) for analyses of milk samples, and to the farm crew at the South Dakota State University Dairy Research Unit (G. A. Stegeman, manager) for care of the cows and assistance with data collection. The dried CDG used in this research were purchased from Broin Enterprises, Inc. (Scotland, SD).
- Corn distillers grains
- Lactating cows
- Ruminally protected amino acids