Residues from anabolic preparations after good veterinary practice

The purpose of this study was to determine the endogenous concentrations of estrogens, particularly estradiol-17beta (E2beta, in edible tissues of beef cattle (females and intact and neutered males) and the concentrations of E2beta, and trenbolone beta and alpha (betaTb, alphaTb) after an E2beta and/or trenbolone acetate (TA) ear implant. Radioimmunoassays were validated for quantitation of E2beta (active isomer), E2alpha, estrone (E1), betaTb and alphaTb for bovine muscle, liver, kidney and fat tissues. The criteria of accuracy, precision, specificity and sensitivity were applied according to the standards of the U.S. Food & Drug Administration. In steer tissues, endogenous E2beta was <15 ppt, as was heifer muscle; but heifer liver and kidney were 3-fold greater. An E2beta implant in steers had no effect on muscle E2beta concentration, but increased E2beta in liver and fat 4- and 3-fold, respectively, but by 24 h post-implant removal, E2beta had fallen by half. Tissue E1 concentrations in cyclic females were similar to E2beta, but rose many fold greater than did E2beta during gestation; E2beta rose 3-fold during gestation. After E2beta/TA implant, steer tissues had E2beta concentrations equal to (for muscle and fat) and one-half (for liver) the E2beta measured in E2beta implant only steers; betaTb was in a low range (250-380 ppt) in muscle, liver and fat and alphaTb was even lower, except in liver (800-1500 ppt). An implant of TA only (no E2beta) resulted in betaTb and alphaTb concentrations 2-3-fold greater in liver, kidney and fat, but no greater in muscle than betaTb in tissues of E2beta/TA implant steers. In conclusion, anabolic implants in steers resulted in tissue E2beta concentrations less than the FDA allowable increment and betaTb in the lowest quartile (0.25) of a part per billion 30 days after implant.