PROTEIN DENSITY AND ITS INFLUENCE ON METABOLITE CONCENTRATION AND NITROGEN-RETENTION BY HOLSTEIN COWS IN LATE-GESTATION

Multiparous Holstein cows in late gestation were used in a completely randomized design to test the effects of prepartum protein supply on p repartum N balance, blood metabolite and hormone concentrations, and p ostpartum intake and milk production. Cows were assigned to one of thr ee isocaloric diets that differed in amount of total dietary crude pro tein (CP) (10.6, 12.7, or 14.5% of dry matter) but not in CP degradabi lity or solubility. Al diets contained the following ingredients: corn silage, chopped grass hay, ground corn, soybean meal, expeller soybea n meal, minerals, and vitamins. Following parturition, all cows were o ffered a similar diet. Nitrogen balance was measured on d 12 to 7 prio r to the expected calving date. Cows were bled on d 5 prior to the exp ected calving date from just prior to feeding to 8 h postfeeding. As d ietary CP increased, plasma glucose concentrations increased linearly, but no change was detected in plasma nonesterified fatty acids or ser um insulin concentrations. Nitrogen intake, apparent and true digestib ilities, fecal and urinary concentrations, and N balance increased as the concentration of dietary protein increased. The efficiency of abso rbed protein utilization decreased as protein intake increased. No cha nge in postpartum intake or milk production was observed. An increase in N retention in late gestation cows that were in a positive N balanc e did not increase postpartum milk production.