Determination of serum insulin concentration during intravenous glucose tolerance testing of healthy bulls

OBJECTIVE: To determine the insulin response curve during IV glucose tolerance testing of mature Holstein bulls. ANIMALS: 8 Holstein bulls between 5 and 8 years old and weighing between 911.5 and 1035.5 kg. PROCEDURE: A 50% glucose solution was rapidly administered IV so that each bull received a mean dose of 258 mg of glucose/kg of body weight. Serum glucose and insulin concentrations were determined before and 30, 60, 120, and 240 minutes after glucose infusion. RESULTS: Serum glucose concentrations 30 and 60 minutes after infusion were significantly greater than baseline concentration. Concentrations returned to baseline values 120 minutes after infusion. Serum insulin concentration was significantly greater 30 minutes after glucose administration, compared with baseline and 240-minute concentrations. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous glucose tolerance testing of mature Holstein bulls resulted in a characteristic insulin response curve. Baseline and peak insulin concentrations were higher in these bulls, compared with values reported for mature Norwegian Red cows.