To evaluate the ability of glucagon to improve carbohydrate status in dairy
cows without an increase in blood lipids, glucagon was infused intravenous
ly for 48 h into lactating cows and spayed heifers in three crossover exper
iments. 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 1
0 mg/d of glucagon into eight heifers; each heifer received two of the dosa
ges. In Experiment 3, four early lactation cows were treated with 5 and 10
mg/d of glucagon. Glucagon consistently increased plasma glucose concentrat
ions in a dose-dependent fashion throughout the 48-h periods. Plasma insuli
n 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 wer
e increased by glucagon at 10 mg/d during Experiment 2. Concentrations of P
-hydroxybutyrate were increased only by the 20-mg/d dosage. During Experime
nt 1, liver glycogen concentrations decreased by 2.1% (wet weight basis) fo
r 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 prod
uction were decreased during Experiment 1. Glucagon improved carbohydrate s
tatus 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.