Materials and Methods
Diets were all balanced to contain 18.0% CP and 11.1% rumen undegradable protein (RDP) (Table 1). Roasted soybeans, blood meal, and corn gluten meal were used to try to equalize the estimated lysine and methionine in the RUP. Tallow and roasted soybeans were added to equalize fat concentration among diets. Soybean hulls and corn were varied to provide 41.5, 40.0, 38.5, 37.0, 37.0, and 37.0% nonfiber carbohydrates in the high forage control; low, medium, and high brewers grains; whole cottonseeds; and EasifloÒ cottonseed (linters matted down by cornstarch) diets; respectively. The NDF in wet brewers grains was corrected for protein contamination (49.2% NDF and 12.2% neutral detergent insoluble CP = 37.0% corrected NDF). Forage NDF was balanced to be 20.8, 18.7, 16.7, 14.7, 14.7, and 14.7%, respectively. Net energy of lactation was balanced to be 1.78, 1.75, 1.72, 1.69, 1.72, and 1.72 Mcal/kg of DM, respectively, using tabular data.
Cows were fed a standardization diet from week 8 to 9 of lactation and were randomly assigned to treatments from week 10 to 25. All data were analyzed using Proc Mixed for a randomized complete block design (cows were blocked for parity, calving date, and expected milk production) with repeated measures. Because no treatment x time interactions were detected, data shown represent the least squares means averaged over time and adjusted for covariates.