Metabolic responses of lactating dairy cows to 14-day intravenous infusions of glucagon

Twenty cows were assigned at parturition to two groups to study metabolic e ffects of continuous intravenous infusions of glucagon. Groups were control cows and cows treated with glucagon at 10 mg/d for 14 d starting at d 21 p ostpartum Daily blood samples and nine liver biopsies were taken from d 7 t o 49 postpartum. Plasma glucagon increased six- to sevenfold during infusio ns of treated cows. Plasma insulin was increased heterogeneously by glucago n infusions. Plasma glucose increased 11.5 and 9.0 mg/dl during wk 1 and 2 of glucagon infusions. No other plasma metabolites tested (nonesterified fa tty acids, beta-hydroxybutyrate, and urea N) were affected by glucagon infu sions. Liver glycogen decreased by d 2 of glucagon infusion but was replete d to preinfusion values by d 7 and increased to 169% of the preinfusion bas eline values at 3 d after cessation of glucagon. Milk production decreased transiently during glucagon infusions. Both milk production and milk protei n percentage decreased during glucagon infusion, which could imply a decrea sed availability of amino acids for milk protein synthesis. Feed intakes di d not increase during glucagon infusions, which was in contrast to the cont rol group. Results indicated that glucagon infusions caused liver glycogeno lysis initially and probably enhanced gluconeogenesis but glucagon did not appear to increase lipolysis from adipose tissue in these early lactating d airy cows.