Identifier

etd-03092012-140419

Degree

Master of Science (MS)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type

Thesis

Abstract

Two experiments assessed the potential of altrenogest, an artificial progestogen, and deslorelin acetate, a gonadotropin-releasing hormone (GnRH) agonist, for suppressing estrus and ovulation in cyclic mares. In the first experiment, mares were administered a luteolytic dose of prostaglandin-F2á on d 6 of diestrus, and were then treated with 1 of 3 formulations of altrenogest in slow-release vehicle (6 mares/group): 1) Biorelease altrenogest LA150 (225 mg total as a 1.5 mL injection); 2) Biorelease altrenogest LA225 (225 mg total as a 1.0 mL injection); or 3) Biorelease altrenogest LA225 (450 mg total as a 2.0 mL injection). Six control mares received vehicle. Compared to control mares (10.0 days), time to ovulation was greater (P < 0.01) for all mares receiving altrenogest (17.5 days overall); there was no difference (P > 0.5) among groups receiving altrenogest. Control mares (6 out of 6) first displayed estrus an average of 4.5 days after prostaglandin-F2á injection; of the 18 mares receiving altrenogest, 11 displayed first estrus at an average of 13.5 days (P < 0.02 relative to controls) and there was no difference (P > 0.19) among groups. It was concluded that the 3 formulations of altrenogest were equally effective in delaying estrus and ovulation in cyclic mares. It is suggested that a 10-day injection interval could be used to keep mares out of heat for extended periods of time. The second experiment was similar to the first, except that there were 2 groups: 1) control mares that received a vehicle injection and 2) mares that received an i.m. injection of 1.5 g of deslorelin acetate in biodegradable microparticles. Administration of deslorelin did not affect (P > 0.1) the day of first onset of estrus or the day of ovulation. There was a tendency (P = 0.08) for deslorelin treated mares (3 out of 7 vs. 0 out of 6 controls) to not show estrus at the expected time, even though they experienced luteolysis and ovulation. It was concluded that injection of 1.5 g of deslorelin acetate was not an effective method for suppressing estrus and ovulation in cyclic mares.

Date

2012

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Thompson, Donald L., Jr.

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