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Trenbolone, Estradiol-17ß and Estrone Levels in Plasma and Tissues and Live Weight Gains of Heifers Implanted with Trenbolone Acetate^1,2,

Clemson University, Clemson, SC 29631

Abstract

Twenty-four heifers were allotted into three groups of eight heifers each and designated control, long-term (LT) or short-term (ST). Animals in the latter two groups were implanted in the ear with 300 mg trenbolone acetate (TBA) for 99 or 62 d, respectively. Four heifers in each group were subjected to liver and fat biopsy 60 d after initiation of the experiment. At slaughter, which occurred 15 d after retrieval of the implant, liver and fat were also collected. The implant was analyzed for residual trenbolone (TBOH), and tissues were analyzed for TBOH and estradiol-17ß (E₂ß). Blood samples were taken weekly after implantation and daily for 14 d before and after implantation. All heifers were weighed weekly. The ST heifers gained faster (P<.05) than the control or the LT heifers, wheras the LT heifers gained similarly to the controls. Plasma levels of TBOH rose to over 900 pg/ml in response to the implantation in both treated groups, but stabilized at a lower level in the ST group than in the LT group. In both groups plasma E₂ß rose to over 7.5 pg/ml in response to TBA implantation; in fact, a regression analysis of E₂ß on TBOH in individual cows showed that the two hormones varied directly. Fat and liver accumulated substantial TBOH during implantation, but it cleared rapidly during the 15 d withdrawal period. Indications from this experiment are that TBA has promise for promoting rate of gain and efficiency of feed utilization in feedlot heifers. No undesirable effects on carcass quality were detected. The drug cleared blood and tissues rapidly after the implant was withdrawn. Further research is needed to determine the most effective implantation schedule. It would be desirable to determine whether a positive response to TBA will occur in animals being finished predominantly on forages.

¹ Published with the approval of the Director of the South Carolina Agr. Exp. Sta. as technical contribution No. 1941.

² The authors gratefully acknowledge Dr. Larry Grimes, Dept. of Exp. Statist.; Sandra Grey for technical assistance; Margie McAlhany and Robin Dill for animal care and Drs. J. C. Bouffault (Agrovet Div.) and J. R. Schied (Research Div.) of Roussel UCLAF, Paris, France, for advice and to the company for monetary support.

³ Dept. of Food Sci.

⁴ Dept. of Anim. Sci.