Supplemental Niacin for Lactating Cows Fed Diets of Natural Protein or Nonprotein Nitrogen

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Abstract
Holstein cows, 16 in early and 16 in midlactation, were assigned to 4 treatments: soybean meal protein plus niacin; soybean meal without niacin; nonprotein N plus niacin; and nonprotein N without niacin. Niacin dose was 6 g/day, and nonprotein N supplied 20% of total N for those treatments. Differences between treatments in milk yields were not significant, but milk persistencies tended to be highest for cows in early lactation fed niacin during wk 9 and 10 of treatment. Intakes of dry matter did not differ signficantly, but cows fed nonprotein N without niacin had lowest intakes per 100 kg body weight. Differences between treatments in feed utilization, milk composition, body weight changes, plasma ammonia, rumen pH, rumen volatile fatty acids, dry matter digestibilities, N digestibilities and retained N were not significant.