Metabolic responses of lactating dairy cows to exogenous glucagon

Fatty liver is a major metabolic disorder of dairy cows in early lactation that compromises their health status and reproductive performance and in clinical cases decreases milk production and feed intake. Fatty liver can be treated with 14-d continuous, intravenous infusions of 10 mg/d of glucagon. The objective of the current study was to test whether treatment of fatty liver with 14-d subcutaneous injections of glucagon at 7.5 or 15 mg/d, which is more practical than infusion, would cause similar metabolic responses and improve health status and reproductive performance of dairy cows in early lactation. In the main study, multiparous Holstein cows (n = 32) were grouped on the basis of their liver triacylglycerol concentration at d 8 postpartum into “Normal” (n = 8; triacylglycerol < 1% liver wet wt) and “Susceptible” (n = 24; triacylglycerol > 1% liver wet wt) cows. “Susceptible” cows were assigned randomly to three groups and beginning at d 8 postpartum received 0 (same for “Normal” cows), 2.5, or 5 mg of glucagon in 60 ml 0.15 M NaCl by subcutaneous injections every 8 h for 14 d. Subcutaneous injections of 15 mg/d of glucagon consistently increased concentrations of plasma glucose and insulin for 4 h, decreased concentrations of liver triacylglycerol in cows older than 3.5 years, and tended to decrease concentrations of plasma NEFA and BHBA. The effects of 15 mg/d of glucagon were not limited to the treatment period, because glucagon decreased the incidence of mastitis and days to first ovarian activity after the injection period. These results document that subcutaneous injections of 15 mg/d of glucagon improve metabolic status throughout the injection period and have the potential to treat fatty liver in older cows. The improved metabolic status in cows treated with 15 mg/d of glucagon in early lactation has long-term beneficial effects by improving health status and reproductive performance during the entire lactation.