Serum concentrations of trenbolone-17(beta) and estradiol-17(beta) and performance of heifers treated with trenbolone acetate, melengestrol acetate, or estradiol-17(beta)

The effects of the growth-promoting steroids estradiol-17[Beta] ([E.sub.2]), trenbolone acetate (TBA), and melengestrol acetate (MGA) in heifers on serum concentrations of [E.sub.2] and trenbolone-17[Beta] (TBOH) were examined. Feed intake and growth performance were also measured. Serum concentrations of [E.sub.2] and TBOH were measured on d 0, 1, 3, 5, 7, 13, 21, 28, 42, 56, 84, 112, and 140 in finishing heifers administered the following treatments: 1) control; 2) MGA, .5 mg per heifer daily; 3) Revalor-H (140 mg TBA + 14 mg [E.sub.2]); 4) Revalor-H + MGA; 5) Finaplix-H (200 mg TBA); and 6) Finaplix-H + MGA. Revalor-H implantation (Treatments 3 and 4) increased (P < .05) serum [E.sub.2] concentrations; peak concentrations (67.5 pg/mL) occurred between d 21 and 56. Feeding MGA (Treatment 4) had no effect (P > .05) on this increase in serum [E.sub.2] concentrations (63.3 pg/mL). From d 84 until d 140, serum [E.sub.2] was greater (P < .05) for the Revalor-H treatment (average of 19 pg/mL) than for the control (7 pg/mL) or Finaplix-H treatments (6.5 pg/mL). Serum [E.sub.2] concentrations increased numerically two- to threefold from d 56 to 140 in controls fed MGA, compared with controls not fed MGA. There was the expected increase in serum TBOH concentrations after TBA implantation in the Revalor-H and Finaplix-H treatments; concentrations were similar (P > .05) for Revalor-H (221 pg/mL) and Finaplix-H (280 pg/mL). After d 56, serum TBOH concentrations decreased in both treatments to 10 and 20% of these concentrations, respectively. Feeding MGA increased serum TBOH (P < .05). Dry matter intake by heifers did not differ among treatments. Feeding of MGA improved gains (P = .12) and efficiencies (P < .01) in nonimplanted heifers and had no effect (P > .4) on gains or efficiencies in Finaplix-implanted heifers. Key Words: Cattle, Trenbolone, Estradiol, Growth Promoters, Growth, Anabolic Steroids