Developmental changes in clearance of intravenous doses of glucose, acetate and β-hydroxybutyrate from plasma of calves

To characterize the effects of diet and age on the post-absorptive use of fermentation end-products, calves were subjected before and after weaning to plasma glucose, beta-hydroxybutyrate and acetate clearance tests. Twenty-four one-week old male Holstein calves were assigned to one of four starter feeds, in a complete random design: (1) control; (2) 10% alfalfa; (3) 20% alfalfa: and (4) cracked corn. Starters were fed ad libitum. Starter intake, carcass-adjusted body weight gain and post-weaning rumen pH were higher in calves consuming alfalfa. Final bodyweights of calves fed alfalfa were 9.5 kg higher than calves given the other diets. With 20% alfalfa, papillae in the caudal ventral blind sac of the rumen were taller than with cracked corn and narrower than on the control. Rumen concentrations of volatile fatty acids were not affected by diet but the acetate:butyrate ratio and pH were higher on d 54 with 20% alfalfa compared to the control. Glucose clearance and flux rates increased significantly from d 11 to 39 but were unaffected to d 53. Increases in plasma beta-hydroxybutyrate and acetate concentrations with age were accompanied by corresponding increases in BHB and acetate fluxes, respectively, but no change in the clearance rate constants. There was little effect of diet on clearance of the plasma metabolites. By 8 weeks of age, glucose was cleared from plasma at 2%/min, beta-hydroxybutyrate at 16%/min, and acetate at 24%/min. Because of relatively low plasma concentrations of beta-hydroxybutyrate and acetate due to incomplete rumen development, glucose remained the predominant energy source for all calves at 8 weeks. (C) 2008 Elsevier B.V. All rights reserved.