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Acute and Chronic Effects of Gonadotropin Releasing Hormone on Reproductive Characteristics of Rams during the Nonbreeding Season^{1 ,2,}

U. S. Department of Agriculture^{3 ,4,}, Clay Center, NE 68933

Abstract

Acute and chronic effects of gonadotropin releasing hormone (GnRH) administration on reproductive characteristics of 32 rams have been assessed during the nonbreeding season. Rams injected intramuscularly with 50 µg of GnRH had elevated (P<.01) concentrations of serum testosterone and noticeably higher (60%) mating activities when compared to control animals injected with saline. Daily injections of GnRH resulted not only in higher testosterone concentrations and mating activity, but also in increased testes size (P<.05). The apparent change in testicular function may account for the improvement in semen quality which was observed in these animals. Although benefits were only slight for percentages of live sperm, normal sperm and sperm with normal acrosomes, sperm motility was markedly increased (P<.05).

These data suggest that reproductive performance in rams is related to testicular androgen secretion and that a spring decline in those characteristics normally associated with high fertility in the male can be lessened by chronic treatment with GnRH.

¹ The authors gratefully acknowledge the statistical assistance of Mr. Brad Knapp and the laboratory expertise of Ms. Marti Brown. Cooperation of the Nebraska Agricultural Experiment Station, University of Nebraska, Lincoln, is acknowledged.

² Gonadotropin releasing hormone was generously supplied by Dr. S. K. Webel, Abbott Laboratories.

³ U.S. Meat Animal Research Center, Agricultural Research Service.

⁴ Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.