Effects of Whole Cottonseed, Niacin, and Niacinamide on In Vitro Rumen Fermentation and on Lactating Holstein Cows

In Experiment 1, effects of whole cottonseed (0, 5, 15, or 30% of the total ration DM) on in vitro ruminal fermentation showed increased ruminal pH and ammonia concentration but lowered microbial protein. Acetic acid concentration was greatest with diets of 15 and 30% whole cottonseed, but propionate and total VFA concentrations were reduced by increasing whole cottonseed from 0 to 30%. In Experiment 2, neither niacin nor niacinamide (0, 100, 200, or 400 ppm) altered substantially fermenter pH or ammonia concentration. Both niacin and niacinamide increased synthesis of microbial protein. Acetate and propionate concentrations were not altered by treatment. Total VFA concentration tended to be lower as concentration of niacin and niacinamide increased. In Experiment 3, 28 Holstein cows were used to determine the effects of supplemental niacin on feed intake, milk yield, and composition. Cows were fed individually complete mixed diets ad libitum containing either: 1) 0; 2) .015; 3) .03; or 4) .06% niacin. There was a trend for lower milk fat test with niacin supplementation. Milk protein percentage was higher without niacin than with niacin at .015 or .03% in the diet, but daily milk and protein yields were higher with .06% versus .015% of niacin. Supplemental niacin did not affect casein nitrogen, lactose or minerals percentage, or concentrations of plasma glucose and insulin.