Effects of nonfiber carbohydrate and niacin on periparturient metabolic status and lactation of dairy cows.

Fifty Holstein cows and 25 Holstein heifers were used in a randomized complete block design. Treatments were a standard nonfiber carbohydrate diet beginning at 19 d prepartum, a high nonfiber carbohydrate diet beginning at 19 d prepartum, a standard nonfiber carbohydrate diet plus niacin (12 g/d) beginning at 19 d prepartum, a high nonfiber carbohydrate diet plus niacin beginning at 19 d prepartum, and a standard nonfiber carbohydrate diet beginning at 19 d prepartum plus niacin beginning at 14 d postpartum. Treatments were applied through 40 wk postpartum. Niacin did not significantly affect production parameters or blood and liver metabolites. Prepartum intakes of dry matter and energy and energy balance were greater for cows and heifers fed the high nonfiber carbohydrate diets. Plasma glucose concentrations tended to be significantly higher, and nonesterified fatty acids and beta-hydroxybutyrate concentrations were significantly lower, when animals were fed diets that were high in nonfiber carbohydrates. Diets containing high nonfiber carbohydrates increased concentrations of liver glycogen and tended to reduce concentrations of liver triglyceride. Milk production tended to be higher, milk fat percentage tended to be lower, and milk protein percentage and production were significantly greater when diets that were high in nonfiber carbohydrates were fed. An increase in dietary nonfiber carbohydrates improved the metabolic parameters during the transition period and improved lactation performance.