Effects of Whole Cottonseed or Niacin or Both on Casein Synthesis by Lactating Holstein Cows

Abstract Forty Holstein cows in late lactation were offered diets containing niacin and whole cottonseed: 1) 0 g/d, 0% 2) 0 g/d, 15% 3) 6 g/d, 0% and 4) 6 g/d, 15%, to evaluate effects on milk case in synthesis. Cows fed diet 1 had the highest DMI. The FCM (21.4 vs. 18.7 kg/d) and milk fat percentage (4.08 vs. 3.81) were higher for cows fed diet 1 than for those fed diet 4. Milk protein percentage (3.61 vs. 3.50) was higher for cows fed diet 1 than for those fed diet 2. Case in N, as a percentage of total N, was higher (71.9 vs. 68.0%) in milk from cows fed diet 1 than those fed diet 3. Insulin tended to be elevated in cows on the diets containing niacin, but glucose was not affected. Plasma niacin was elevated in cows on the diets supplemented with niacin compared with diet 1. Plasma AA were changed only slightly by treatments. The beneficial effect of niacin on milk case in synthesis, noted in our earlier work when cows were fed whole cottonseed, was not evident in this study with cows in late lactation and during hot weather.