Animal Science Department


Date of this Version



In Proceedings of the American Society of Animal Science Midwest Section, March 19-21, 2012. Des Moines, IA. J. Anim. Sci. 90 (suppl 2): p 81.


Two identically designed studies were conducted in separate years at the UNL Haskell Agricultural Laboratory using 192 crossbred heifers (96/study). Within a study heifers (initial weight = 386kg) were randomly assigned to 2 groups (3 42.4 m × 14.6 m pens/group/year): 1) treatment (TRT) animals were administered synthetic hormones via subcutaneous implants [d 1, 36 mg zearalonal; d 35, 140 mg trenbolone acetate (TBA) and 14 mg of 17β-estradiol benzoate (Revalor-H)] and fed Melengesterol Acetate (MGA), and 2) control (CON) animals with no synthetic hormone provided. Throughout each study, feedlot pen surface samples were obtained from 4 equally-sized zones (5 surface sub-samples obtained/zone) within each pen. Runoff to waste water collection basins was also sampled. Run-off water and pen surface samples, including fresh manure, were analyzed for 16 natural and synthetic steroid hormones and their metabolites. Statistical model included year, treatment, replicate and year x treatment interaction. In pen surface samples, obtained at trial termination (d 109 for study 1 and d 138 for study 2), 4-androstenedione, andosterone, 17β-estradiol, estrone, α-zearalanol, and MGA were greater (P < 0.05) for TRT while progesterone and 17α-hydroxyprogesterone were greater for CON. With the exception of androsterone, average hormonal concentrations in pen surface samples were less than 11 ng/g. In runoff samples, 4-androstenedione was greater for TRT and progesterone was greater for CON. Low (55 ng/g) concentrations of 17α-trenbolone, a metabolite of TBA, was detected in fresh manure from TRT group samples collected shortly after implanting, however no TBA metabolites were detected in pen surface samples. Gains and feed conversions were 18.6 (P < 0.05) and 7.2% better, respectively, for TRT, while CON had 16.7% greater choice and prime carcasses. Results indicate that low levels of both natural and synthetic hormones are found in cattle waste, although TBA metabolites were not found in run-off or pen surface samples.