Effects of zeranol and trenbolone acetate on testis function, live weight gain and carcass traits of bulls

Silcox, R.W.; Keeton, J.T.; Johnson, B.H.

Journal of Animal Science 63(2): 358-368


ISSN/ISBN: 0021-8812
PMID: 3759674
Accession: 001355249

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Sequential implantation of young bulls with 36-mg zeranol at 56-day intervals, beginning at 100 or 150 days of age, significantly reduced testis growth, sperm production and serum testosterone concentration in response to 200 micro g GnRH. Treatment at 200 or 250 days of age had no effect. Body weights were similar to untreated controls in all groups. In another experiment, bulls previously implanted with zeranol at 175 and 231 days of age received single implants of zeranol, trenbolone or trenbolone plus zeranol at approx. 300 days of age. At slaughter (135 days later), body weight and carcass characteristics in all treatments were similar to untreated controls. However, trenbolone reduced sperm production (P<0.05), zeranol reduced sperm production and testes weight (P<0.05), but trenbolone plus zeranol had no effect. Mean testosterone response to GnRH was significantly suppressed in all implant groups on day 65, but only in trenbolone or trenbolone plus zeranol groups on day 112. Results indicate that zeranol suppresses spermatogenesis and testosterone production if implanted before approx. 200 days of age, and that no benefit is derived from implanting bulls with both trenbolone and zeranol.