Metabolic responses of dairy cows and heifers to various intravenous dosages of glucagon

To evaluate the ability of glucagon to improve carbohydrate status in dairy cows without an increase in blood lipids, glucagon was infused intravenously for 48 h into lactating cows and spayed heifers in three crossover experiments. During Experiment 1, glucagon (5 and 20 mg/d) was infused into four midlactation cows. Experiment 2 involved the infusion of 0, 2.5, 5.0, or 10 mg/d of glucagon into eight heifers; each heifer received two of the dosages. In Experiment 3, four early lactation cows were treated with 5 and 10 mg/d of glucagon. Glucagon consistently increased plasma glucose concentrations in a dose-dependent fashion throughout the 48-h periods. Plasma insulin was increased in a nondose-dependent manner by glucagon in Experiment 1. Plasma urea N was increased when glucagon was administered at 5 mg/d during Experiment 2 and tended to be decreased during Experiment 3. Nonesterified fatty acids in plasma were, in most cases, not affected; however, they were increased by glucagon at 10 mg/d during Experiment 2. Concentrations of P-hydroxybutyrate were increased only by the 20-mg/d dosage. During Experiment 1, liver glycogen concentrations decreased by 2.1% (wet weight basis) for both dosages of glucagon, and concentrations of total lipid in the liver were increased by 0.6% (wet weight basis) by 20 mg/d of glucagon. Milk fat percentage was increased by glucagon, but milk volume and milk protein production were decreased during Experiment 1. Glucagon improved carbohydrate status over the 48-h periods in all experiments but did not increase plasma nonesterified fatty acids except at the 10-mg/d dosage in Experiment 2.