Plasma Concentrations of Metabolic Hormones in High and Low Producing Dairy Cows

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Abstract
Concentrations of insulin, glucagon, growth hormone, adrenocorticotropin, and cortisol were determined in plasma samples obtained at 20-min intervals for 6 h from low and high producing dairy cows at d 30 and 90 postpartum. Four nonpregnant, nonlactating cows also were also sampled. Insulin concentrations were reduced at d 30 in both groups of lactating cows compared with concentrations in nonlactating cows; glucagon concentrations were unchanged. The molar insulin:glucagon was reduced at d 30 in both groups and at 90 d for low, but not high producers. Growth hormone concentrations were higher at d 30 in high producers than at d 90, in low producers at d 30, and higher than in nonlactating cows. Cortisol concentrations were lower in high producing cows at d 30 than at d 90 or in nonlactating cows due to a reduced pulse amplitude. No differences were observed for adrenocorticotropin. Reduced molar insulin:glucagon may be an integral response of the cow to lactation, while the difference in the insulin:glucagon for high and low producers at d 90 postpartum may indicate a continued need for a gluconeogenic stimulus in low producers. The elevated growth hormone and low cortisol concentrations likely participate in the enhanced production observed in high producing dairy cows.