Master of Science (MS)


Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type



Seven experiments were performed to assess the use of glucose responses to insulin injections as a means of estimating insulin sensitivity in horses; to compare the insulin sensitivities of normal horses vs. those displaying hyperleptinemia; and to put this method into practical application. Experiment 3.1 examined dose-responses in mares of potentially different insulin sensitivities. Recombinant human insulin was injected at doses of 8, 20, 50, and 125 mU/kg BW, as needed, to estimate the dose of insulin causing a 50% decrease in glucose concentrations (ED50). Five mares each of low leptin concentrations (LL) and low BCS, LL and high BCS, and high leptin concentrations and high BCS, were studied. The ED50 was similar for LL mares, regardless of BCS, and was lower (P < 0.01) than for mares with high leptin concentrations. It was concluded that a dose of 50 mU/kg BW of recombinant human insulin could be used safely to start the dose-response curve; lower or higher doses could then be used to estimate ED50. Experiment 3.2 assessed the repeatability of the estimates for ED50 obtained in Exp. 3.1. Estimates obtained were highly correlated (R2 = 0.822) with those obtained in Exp. 3.1, with an average within-mare CV of 8.9%. The next five experiments studied the effects of 1) prior administration of epinephrine, 2) overnight feed deprivation versus hay or pasture consumption, 3) 10-d acclimatization to hay in a dry lot versus pasture grazing, 4) cinnamon extract supplementation, and 5) fish oil supplementation on insulin sensitivity. Epinephrine stimulated blood glucose (P < 0.05) and prevented the insulin-induced decrease in blood glucose in both sensitive and insensitive mares. Overnight feed deprivation decreased (P < 0.06) insulin sensitivity relative to overnight ad libitum access to hay, and both regimens resulted in reduced insulin sensitivity relative to overnight pasture availability. Ten days of hay consumption in a dry lot reduced (P < 0.05) insulin sensitivity in insensitive mares relative to pasture grazing. Supplementation with cinnamon extract or fish oil had no effect on insulin sensitivity of mares with known low insulin sensitivity under the conditions of these experiments.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Thompson, Donald L. Jr.