Response of Insulin, Glucagon, and Growth Hormone to Intravenous Glucose Challenge in Cows Fed High Fat Diets

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Abstract
Effect of feeding high fat diets on peripheral plasma concentrations of immunoreactive insulin, glucagon, and growth hormone following intravenous glucose challenge (100 mg D-glucose/kg body weight) at 50 and 100 d of lactation in 16 multiparous Holstein cows was evaluated. The high fat diet contained 18.5% whole cottonseed on a dry matter basis as the source of extra dietary fat. Feeding the high fat diet had no apparent effect on energy balance. Basal plasma insulin and insulin:glucagon ratio were increased in cows fed the high fat diet relative to those of controls. Glucagon, insulin, and insulin:glucagon ratio response to glucose challenge were not affected by diet. Response of growth hormone to glucose challenge at 50 d of lactation was depressed in cows fed the high fat diet. Plasma glucose peaked at greater concentrations in cows fed the high fat diet. Feeding a high fat diet to dairy cows appears to increase basal insulin concentration and insulin:glucagon ratio, which has actions opposed to glucose synthesis. Thus, endocrine effects of a high fat diet appear to favor decreased milk production.