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Effect of Unilateral Castration and Unilateral Cryptorchidism on Gonadotropin and Testosterone Response to Gonadotropin Releasing Hormone in the Bull^1,2,

Clemson University³, Clemson, SC 29631

Abstract

The effects of unilateral castration (UC) and induced unilateral cryptorchidism (UCR) on basal plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone, and on the responses of these hormones to gonadotropin releasing hormone (GnRH), were investigated in bulls altered at 3, 6 or 9 months of age. Blood plasma was collected before and after GnRH (200 µg) stimulation approximately 1 year following gonadal manipulation. Neither mean baseline concentrations nor GnRH-induced increases in plasma testosterone were altered (P>.1) by hemicastration or UCR (P>.1). Both mean baseline LH and GnRH-induced LH release were greater (P<.05) in bulls altered at 3 months of age than in bulls altered at 9 months of age. UC increased (P>.05) plasma LH response to GnRH over that observed in intact bulls, but not above that in UCR bulls. UCR had no detectable effect on either baseline concentrations or GnRH-stimulated LH release. FSH was increased (P>.05) in hemicastrates, while UCR had a variable effect on peripheral FSH: FSH was reduced (P>.05) in UCR animals altered at 3 months of age but increased (P>.05) in UCR bulls altered at both 6 and 9 months of age when compared to FSH in intact bulls. The results indicate that, compared with intact bulls, UC bulls release increased amounts of both gonadotropins but similar amounts of testosterone in response to GnRH stimulation. UCR had a variable effect on FSH release and did not alter either LH or testosterone.

¹ Technical Contribution No. 1873 of the South Carolina Agr. Exp. Sta., Clemson Univ. Clemson, SC.

² The authors are indebted to K. W. Cheng, Univ. of Manitoba, Winnipeg, Manitoba, Canada, for providing purified bovine FSH and specific bovine FSH antiserum; L. E. Reichert for providing purified bovine LH (LER-1072); T. E. Kiser, Univ. og Georgia, Athens, for providing LH antiserum #190; G. D. Niswender, Colorado State Univ., Ft. Collins, for providing testosterone antiserum, S250, and the Endocrine Study Section, Bethesda, MA, for Providing pituitary hormones.

³ Dept. of Dairy Sci.