Effects of nutrient source and time of feeding on changes in blood metabolites in young calves.

Sixteen Holstein calves were used in a completely randomized design to evaluate effects of dry feed intake and time after feeding on concentration of selected peripheral blood metabolites. Calves entered the study at 13 (SD = 2.9) d of age and were fed milk replacer (10% of BW) twice daily to weaning at 28 (Grain) or 84 (Milk) d and calf starter from 1 (Grain) or 56 (Milk) d. Blood was sampled every 14 d at 0 and 2 h after the morning feeding and analyzed for beta-hydroxybutyrate (beta HBA), glucose, nonesterified fatty acids, urea N, L(+) lactate, and VFA. Blood beta HBA and VFA increased with increasing dry feed intake, but particularly at 2 h postfeeding. Molar proportion of VFA as acetate declined and propionate and butyrate increased with increasing feed intake. Glucose at 2 h postfeeding declined after weaning to levels lower than 0-h values. Prefeeding glucose concentrations increased with increasing grain intake. Lactate declined throughout the study without effect of treatment or time after feeding. Data indicate that marked changes occur with increasing grain intake and time after feeding. Increased blood beta HBA seems to be a response to alimentary ketogenesis.