J. Anim Sci.
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J. Anim Sci. 1986. 62:1332-1339.
© 1986 American Society of Animal Science
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Effects of Pulsatile Injection of GnRH into 6- to 14-Wk-Old Holstein Bulls1

C. J. Miller and R. P. Amann

Colorado State University2, Fort Collins 80523

Abstract

With the goal of hastening puberty, we evaluated the effects of dose of gonadotropin releasing hormone (GnRH) during pulsatile injection on luteinizing hormone (LH) secretion in bulls 6, 10 or 14 wk old, and of pulsatile administration of GnRH every 2 h to bulls from 6 to 12 wk of age on reproductive development. Based on response to the last three of 12 bihourly injections of 20, 200 or 2,000 ng GnRH/kg, only the two higher doses of GnRH induced secretion of LH at 6 wk. At all ages, 200 ng GnRH/kg induced maximal discharges of LH. Based on comparisons between seven treated bulls and their identical twins, bihourly injections of GnRH starting on d 42 elicited discharge of LH for 34 d in progeny of one sire and >28 d but <42 d in progeny of another sire. After 14 d of treatment, both elicited and spontaneous discharges of LH were smaller in all treated bulls. Within 2 d after cessation of GnRH injections on d 84, LH discharges were similar in frequency and amplitude in treated and control twins. Testicular and body growth were similar in treated and control bulls, but puberty was delayed (P<.05) in bulls in which exogenous GnRH suppressed endogenous discharges of LH.

Footnotes

1 Supported in part by the Colorado State Univ. Exp. Sta., the Natl. Assoc. of Animal Breeders and the Anim. Reprod. Lab. The assistance of D. J. Marsh for rearing calves, fellow students with blood sampling, and Dr. T. M. Nett and S. M. Hippensteel with hormone assays is gratefully acknowledged. Published with the approval of the Director, Agr. Exp. Sta. as Scientific Series paper 3009.

2 Anim. Reprod. Lab.






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Copyright © 1986 by the American Society of Animal Science.