Effect of Age and Diet on Fasting Blood and Plasma Glucose Levels, Plasma Nonesterified Fatty Acid Levels, and Glucose Tolerance in Dairy Calves1

Fifteen male dairy calves were used to investigate the effects of age and diet on blood and plasma glucose and plasma nonesterified fatty acid levels, and glucose tolerance. Nine Holsteins and six Jerseys, one day old, were placed on one of three diets for a 100-day experimental period. The diets were: (I) milk, fortified with nonfat milk solids, (II) milk plus high-starch concentrate, and (III) milk plus high-fiber concentrate. Once each week a 16-hr fasting blood sample was obtained and 500 mg glucose/kg body weight were administered to each calf for a glucose tolerance test. Blood and plasma glucose levels increased with advancing age in calves fed Diet I. There were decreases in blood and plasma glucose levels with advancing age in calves fed Diet II. Blood glucose declined, whereas plasma glucose levels increased, with advancing age in calves receiving Diet III. No change was detected in plasma nonesterified fatty acid levels with advancing age. Correlations between glucose and nonesterified fatty acid levels were negative and significant. The inverse relationship observed between these metabolites supports the view that nonesterified fatty acids are mobilized to maintain caloric homeostasis during periods of fast. Glucose tolerance decreased with advancing age in calves fed each of the diets, but rates of decrease were not significantly different among diets.