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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #195538
Title: COMPARATIVE RESPONSE OF RAMS AND BULLS TO LONG-TERM TREATMENT WITH GONADOTROPIN-RELEASING HORMONE ANALOGS

Author
item JIMENEZ-SEVERIANO, HECTOR - UNIV NEBRASKA, LINCOLN
item D'OCCHIO, M - UNIV QUEENSLAND, AUSTRALI
item LUNSTRA, DONALD - FORMER ARS EMPLOYEE
item MUSSARD, M - UNIV NEBRASKA, LINCOLN
item DAVIS, T - UNIV NEBRASKA, LINCOLN
item ENRIGHT, W - INTERVET INTERNATIONAL
item KINDER, JAMES - UNIV NEBRASKA, LINCOLN

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2006
Publication Date: 4/20/2007
Citation: Jimenez-Severiano, H., D'Occhio, M.J., Lunstra, D.D., Mussard, M.L., Davis, T.L., Enright, W.J., Kinder, J.E. 2007. Comparative response of rams and bulls to long-term treatment with gonadotropin-releasing hormone analogs. Animal Reproduction Science. 98(3-4):204-224.

Interpretive Summary: Bulls and rams have been reported to differ in their response to long-term gonadotropin releasing hormone (GnRH) treatment, a hormone produced by the brain that controls the release of the gonadotropins luteinizing hormone and follicle-stimulating hormone, which in turn, are hormones that regulate testosterone and sperm production. Specifically, long-term GnRH treatment in rams causes testicular atrophy and decreases testosterone, while the same treatment in bulls does not alter testosterone production. The differences between rams and bulls in the response to treatment with compounds that mimic GnRH and compounds that inhibit GnRH were further explored in this report. Results indicated that both rams and bulls produce testosterone in response to compounds that mimic GnRH; however, bulls produce substantially more testosterone than rams. Both rams and bulls had decreased testosterone in response to GnRH inhibitors, and the inhibition was greater in bulls. Results also indicated that treatment with bulls and rams with compounds that either mimic or inhibit GnRH had relatively long-lasting effects on the release of luteinizing hormone and follicle-stimulating hormone in response to GnRH. Differences in the response to GnRH between species suggest differences in the control mechanisms that govern gonadotropin release, testosterone production and male fertility. Further work is necessary to elucidate these differences.

Technical Abstract: The objective was to compare the relative response between rams and bulls in characteristics of LH, FSH and testosterone (T) secretion, during and after long-term treatment with GnRH analogs. Animals were treated with GnRH agonist, GnRH antagonist, or vehicle (Control) for 28 days. Serial blood samples were collected on day 21 of treatment, and at several intervals after treatment. Injections of natural sequence GnRH were used to evaluate the capacity of the pituitary to release gonadotropins during and after treatment. Treatment with GnRH agonist increased basal LH and T concentrations in both rams and bulls, with a greater relative increase in bulls. Endogenous LH pulses and LH release after administration of GnRH were suppressed during treatment with GnRH agonist. Treatment with GnRH antagonist decreased mean hormone concentrations, LH and T pulse frequency, and the release of LH and T after exogenous GnRH, with greater relative effects in bulls. Rams previously treated with antagonist had a greater release of LH after administration of GnRH compared with control rams, while rams previously treated with agonist showed a reduced LH response. Bulls previously treated with agonist had reduced FSH concentrations and LH pulse amplitudes compared with control bulls while bulls previously treated with antagonist had greater T concentrations and pulse frequency. The present study was the first direct comparison between domestic species of the response in males to treatment with GnRH analogs. The findings demonstrated that differences do occur between rams and bulls in LH, FSH and testosterone secretion during and after treatment. Also, the consequences of treatment with either GnRH analog can persist for a considerable time after discontinuation of treatment.