Identifier

etd-04142005-131028

Degree

Master of Science (MS)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type

Thesis

Abstract

Two experiments were performed to discover what, if any, reproductive differences exist in high body condition (BCS) mares with varying concentrations of leptin. Previous research showed that mares with high body condition scores can have a range of leptin levels, from very low (<5 ng/mL) to very high (>10 ng/mL). Earlier results indicated that most mares with high body condition scores maintain estrous cycles or show significant follicular activity during the winter. Among these high BCS mares, about 30% of them exhibit hyperleptinemia and hyperinsulinemia. The first experiment was designed to compare the reproductive characteristics of high BCS mares with high versus low leptin levels during vernal transition and the first estrous cycle. Also, an IVGTT, insulin challenge, and two sulpiride challenges were performed to characterize endocrine profiles of these mares. Results of these challenges were similar to previous work, in that hyperleptinemic mares had greater insulin responses to glucose and greater clearance rates of infused glucose compared to low leptin mares. These mares also showed a slightly greater prolactin response to sulpiride than their low leptin counterparts. When analyzing the reproductive traits of these mares, no differences between groups existed for follicular sizes or distributions, gonadotropin levels, or date of first ovulation. The second experiment was designed to assess what differences may exist between high BCS mares with high versus low leptin levels with regard to their gonadotropin and ovarian responses to several analogs of gonadotropin releasing hormone (GnRH). Histrelin and deslorelin appeared to be the most potent of the analogs, followed by buserelin and then GnRH. Leptin status did not appear to affect the gonadotropin response or time to ovulation for any of the analogs used in this trial. In conclusion, although hyperleptinemic mares showed altered insulin and glucose characteristics, no significant reproductive differences were observed between these mares and their normal counterparts in terms of ovarian function or the hypothalamic- pituitary axis during vernal transition or the estrous cycle.

Date

2005

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Donald Thompson, Jr.

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