Protein Density and Its Influence on Metabolite Concentration and Nitrogen Retention by Holstein Cows in Late Gestation

Abstract

Multiparous Holstein cows in late gestation were used in a completely randomized design to test the effects of prepartum protein supply on prepartum N balance, blood metabolite and hormone concentrations, and postpartum intake and milk production. Cows were assigned to one of three isocaloric diets that differed in amount of total dietary crude protein (CP) (10.6, 12.7, or 14.5% of dry matter) but not in CP degradability or solubility. All diets contained the following ingredients: corn silage, chopped grass hay, ground corn, soybean meal, expeller soybean meal, minerals, and vitamins. Following parturition, all cows were offered a similar diet. Nitrogen balance was measured on d 12 to 7 prior to the expected calving date. Cows were bled on d 5 prior to the expected calving date from just prior to feeding to 8h postfeeding. As dietary CP increased, plasma glucose concentrations increased linearly, but no change was detected in plasma nonesterified fatty acids or serum insulin concentrations. Nitrogen intake, apparent and true digestibilities, fecal and urinary concentrations, and N balance increased as the concentration of dietary protein increased. The efficiency of absorbed protein utilization decreased as protein intake increased. No change in postpartum intake or milk production was observed. An increase in N retention in late gestation cows that were in a positive N balance did not increase postpartum milk production.