Lactation performance by dairy cows fed wet brewers grains or whole cottonseed to replace forage

Holstein cows starting at wk 8 of lactation were used to evaluate lactation performance when wet brewers grains, whole linted cottonseed, or starch-coated whole linted cottonseed (Easiflo) were substituted for forage. The wet brewers grains were added to diets to decrease forage neutral detergent fiber from 21% incrementally down to 15% while simultaneously decreasing nonfiber carbohydrate concentration from 40.3% down to about 33.8%. The cottonseed treatments all had similar concentrations of forage neutral detergent fiber (15%) and nonfiber carbohydrates (33.1 and 36.0%). Dry matter intake and milk production were similar across treatments. Milk fat percentage was decreased for Easiflo versus whole linted cottonseeds, but no other responses were detected. The current National Research Council (NRC) energy model was evaluated using individual cow data that were averaged over the entire 16-wk treatment period. For treatment means, the output of energy averaged 99% of the net energy of lactation intake, indicating very good corroboration of the model to account for energy usage for a group of cows. However, the ability to predict energy usage for individual cows was less accurate based on the comparison of residuals of observed and predicted body weight change regressed against predicted body weight change, apparently because of compounding of random errors in this prediction, which was alleviated over a larger number of observations. These results also corroborate current NRC guidelines for minimum forage neutral detergent fiber concentrations for lactating cows past the calving transition period.