Identifier

etd-04072009-130600

Degree

Master of Science (MS)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type

Thesis

Abstract

Plasma leptin concentrations in horses have been shown to vary widely. However, many factors may perturb these measurements. Previous research has documented a link between hyperinsulinemia and hyperleptinemia in horses. This condition has been speculated to be associated with components of equine metabolic syndrome, such as insulin resistance and laminitis. However, many of the methods accepted in diagnosing these metabolic abnormalities are expensive and often difficult to perform. Thus, the objectives of the experiments in this thesis were 1) to determine if it is possible to differentiate hyperleptinemic horses from normal ones by hormone manipulation with dexamethasone, a glucocorticoid analog; 2) to evaluate intravenous injection combinations of insulin and glucose to assess insulin sensitivity; and 3) to assess insulin sensitivity in hyperleptinemic and normal horses using two concentrations of exogenous insulin. In the first experiment, it was determined that a single injection of dexamethasone did not enhance the ability to differentiate between hyperleptinemic and normal horses. In the second experiment, the combined intravenous insulin and glucose tests proved to be very simple and inexpensive. However, repeatability among estimates on the same horses was not strong enough to be conclusive or predictive in assessing insulin sensitivity in horses. In the third experiment, a single injection of exogenous insulin at 0.02 IU/kg of body weight proved to be a consistent and efficacious method of differentiating hyperleptinemic from normal horses. Glucose concentrations in hyperleptinemic horses decreased very little (14%) at this insulin dosage compared to those in normal horses that dropped (P < 0.01) 46% from a pre-injection average of 85 to 46 mg/dL 40 min after injection. It was concluded that a low-level insulin injection coupled with routine plasma leptin estimates constitute a simple method of identifying hyperleptinemic horses.

Date

2009

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Donald L. Thompson, Jr.

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