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Effects of Zeranol on the Reproductive System of Lambs^{1 ,2,}

University of Connecticut, Storrs 06268

Abstract

Forty-eight crossbred ram lambs were used to determine the effects of Zeranol on the reproductive system. The experiment was a 2 x 2 x 2 factorial design consisting of levels of 0 and 12 mg zeranol implanted at 44 or 89 days of age. The rams were left intact or unilaterally castrated (UC) at 44 days of age and were slaughtered at 139 days of age. Pituitary FSH concentration was significantly decreased by implantation at 89 days. In intact lambs implanted at 44 days the concentration was lower, while in UC lambs it was slightly higher than in the comparable unimplanted groups, resulting in a significant interaction of UC and 44 day implantation. Serum LH concentration at slaughter was significantly depressed by implantation at day 44. Implantation with zeranol at day 44 or 89 significantly decreased, while unilateral castration significantly increased testis weight. In general, treatments that reduced concentrations of pituitary FSH or serum LH also reduced testis weight. There was an interaction of UC and 44 day implantation on seminiferous tubule diameter similar to the interaction observed for the pituitary FSH concentration. The mean percentage seminiferous tubule area did not vary significantly with any treatment suggesting that both tubular and intertubular tissue were affected similarly by treatment. Epididymal weight and tubule diameter were both significantly decreased by day 89 implantation and were increased by UC. This experiment confirms a preliminary observation of a reduction in testis weight due to zeranol implantation and provides data consistent with the hypothesis that zeranol affects testis weight by way of inhibition of gonadotropin synthesis.

¹ Scientific Contribution No. 623, Storrs Agricultural Experiment Station, University of Connecticut, Storrs.

² Supported in part by a grant from Commercial Solvents Corporation, Terre Haute. Anti-ovine LH was supplied by Dr. G. D. Niswender. The purified ovine LH (LER-1056) for Iodination was supplied by Dr. L. E. Reichert, Jr. and NIAMD-R-LH-RP-1 and NIH-LH-5-18 reference preparations were supplied by NIH-NIAMD.

³ The authors wish to thank Mr. Kenneth Parsons for his cooperation while the Iambs were on his farm, and Dr. Bruce Goldman for his assistance with the radioimmunoassay.