Secretion and clearance rates of glucagon in dairy cows

Eight Holstein cows were sampled to examine plasma concentrations of hormones and some energy related metabolites. Sampling was every hour for 12 h at about 2 wk prepartum, at 3 wk postpartum, during an energy restriction ketonemia, and after a recovery period. Cows were fed ad libitum except for four cows induced into ketonemia by restricting feed intake 50%. Pulse doses of glucagon were injected intravenously during each period. Feed restriction increased concentrations of growth hormone, acetoacetate, beta-hydroxybutyrate, and free fatty acids in blood plasma. Concentrations of insulin and glucose showed some tendencies to decrease. Distribution space and turnover rate of glucagon were not different between periods, and pool size was increased in the dry period. Metabolic clearance rate of glucagon was not significantly different between periods. Insulin and glucose concentrations were increased 1 to 2 min after injection of glucagon and remained increased for 25 min. Covariance analysis showed that glucagon injection caused glucose concentration to increase proportionally in all periods, suggesting that cows had equal gluconeogenic capacity in all periods. Basal concentration, pool size, and secretion rate of glucagon showed some tendency to be decreased during ketonemia.