Effects of zeranol implanted during a postweaning weight gain test on testicular, semen, and endocrine characteristics of bulls

James G. Floyd Jr. From the Department of Veterinary Clinical Medicine (Floyd, Ott) and Veterinary Biosciences (Hixon, Veeramachaneni), College of Veterinary Medicine, and the Department of Animal Sciences (Willlms, Parrett), College of Agriculture, University of Illinois, Urbana, IL 61801.

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 DVM, MS
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Randall S. Ott From the Department of Veterinary Clinical Medicine (Floyd, Ott) and Veterinary Biosciences (Hixon, Veeramachaneni), College of Veterinary Medicine, and the Department of Animal Sciences (Willlms, Parrett), College of Agriculture, University of Illinois, Urbana, IL 61801.

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James E. Hixon From the Department of Veterinary Clinical Medicine (Floyd, Ott) and Veterinary Biosciences (Hixon, Veeramachaneni), College of Veterinary Medicine, and the Department of Animal Sciences (Willlms, Parrett), College of Agriculture, University of Illinois, Urbana, IL 61801.

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D. N. Rao Veeramachaneni From the Department of Veterinary Clinical Medicine (Floyd, Ott) and Veterinary Biosciences (Hixon, Veeramachaneni), College of Veterinary Medicine, and the Department of Animal Sciences (Willlms, Parrett), College of Agriculture, University of Illinois, Urbana, IL 61801.

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Clifton L. Willms From the Department of Veterinary Clinical Medicine (Floyd, Ott) and Veterinary Biosciences (Hixon, Veeramachaneni), College of Veterinary Medicine, and the Department of Animal Sciences (Willlms, Parrett), College of Agriculture, University of Illinois, Urbana, IL 61801.

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Douglas F. Parrett From the Department of Veterinary Clinical Medicine (Floyd, Ott) and Veterinary Biosciences (Hixon, Veeramachaneni), College of Veterinary Medicine, and the Department of Animal Sciences (Willlms, Parrett), College of Agriculture, University of Illinois, Urbana, IL 61801.

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Summary

At initiation of a 140-day postweaning weight gain test, Angus bulls were assigned in equal numbers (n = 5) to 1 of 3 treatment groups to determine effects of implantation with zeranol, an estrogenic growth promotant, on selected reproductive characteristics. The bulls, whose age (mean ± sd) was 233 ± 20 days at initiation of the test (day 0), were implanted with 36 mg of zeranol on day 0, on days 0 and 60, or were not implanted. At day 140, scrotal circumference and testicular consistency were unaffected by zeranol implantation. Zeranol implantation did not affect the morphologic characteristics of semen samples collected by electroejaculation on day 159. There was no effect of zeranol treatment on paired weights of testes, epididymides, or vesicular glands from bulls at slaughter 47 to 68 days after day 140. Microscopic lesions associated with estrogenic exposure were not observed in accessory sex glands or epididymides of any bull. Histopathologic changes in the seminiferous epithelium were not induced by zeranol treatment. Implantation with zeranol did not affect body weight or hip weight at day 140 or carcass weight at slaughter. Plasma concentration of luteinizing hormone was increased (P = 0.04), whereas testosterone concentration tended to be less (P = 0.08) in both groups of zeranol-implanted bulls after administration of gonadotropin-releasing hormone on day 140.

Summary

At initiation of a 140-day postweaning weight gain test, Angus bulls were assigned in equal numbers (n = 5) to 1 of 3 treatment groups to determine effects of implantation with zeranol, an estrogenic growth promotant, on selected reproductive characteristics. The bulls, whose age (mean ± sd) was 233 ± 20 days at initiation of the test (day 0), were implanted with 36 mg of zeranol on day 0, on days 0 and 60, or were not implanted. At day 140, scrotal circumference and testicular consistency were unaffected by zeranol implantation. Zeranol implantation did not affect the morphologic characteristics of semen samples collected by electroejaculation on day 159. There was no effect of zeranol treatment on paired weights of testes, epididymides, or vesicular glands from bulls at slaughter 47 to 68 days after day 140. Microscopic lesions associated with estrogenic exposure were not observed in accessory sex glands or epididymides of any bull. Histopathologic changes in the seminiferous epithelium were not induced by zeranol treatment. Implantation with zeranol did not affect body weight or hip weight at day 140 or carcass weight at slaughter. Plasma concentration of luteinizing hormone was increased (P = 0.04), whereas testosterone concentration tended to be less (P = 0.08) in both groups of zeranol-implanted bulls after administration of gonadotropin-releasing hormone on day 140.

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