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Residue Levels of Endogenous Estrogens in Beef Tissues^1,2,3,

Clemson University⁴, Clemson, SC 29631

Abstract

Endogenous estrogen concentrations in edible tissues of cows, bulls and steers were compared with those of steers with estrogen implants. Concentrations are expressed as pg estrogen/g of tissue, wet weight. In addition, depletion rates of estradiol-17β (E₂β) estrone (E₁) and estradiol-17 (E₂) from these tissues and blood plasma were determined. In muscle, the main estrogen was E₂β, regardless of sexual status (nonpregnant cow, bull or steer); however, concentrations approached the lower limits of analytical sensitivity. In liver and kidney, E₂β and E₁ were equimolar (25 to 40 pg/g for each) in heifers and steers, whereas in kidney fat, concentrations of E₁ exceeded those of E₂β. Concentrations of E₁ in fat were slightly higher in bulls than in cows or steers. The predominant estrogen in fat during pregnancy was E₁, with concentrations 150 times greater than those of nonpregnant heifers or nonimplanted steers and 75 times the concentration found in steers with E₂β implants. In kidney of pregnant cows, E₁ rose 40-fold and in liver 10-fold over that of implanted steers. Concentrations of E₂ were low and depleted rapidly after withdrawal of an E₂β implant. Tissue depletion studies of the three estrogens demonstrated that E₁ disappeared from plasma, fat, liver and kidney more slowly than E₂73x03B2; or E₂. Depletion of E₂β from the tissue can be manipulated as shown by the faster rate of depletion in implanted steers than in nonimplanted steers. Because E₁ is cleared from fat more slowly than E₂, and E₁ concentrations are higher, this estrogen-tissue combination should be used to monitor estrogen implants as anabolic agents.

¹ Published with the approval of the Director of the South Carolina Exp. Sta. as Technical Contribution No. 1971.

² The author gratefully acknowledges the contributions of Dr. J. F. Wagner, Dr. R. Basson and Mr. E. L. Veenhuizen, Eli Lilly and Co., Greenfield, IN.

³ Paper presented at the Symposium on "Metabolic Fate of Anabolic Substances in Food Animals" at the meeting of the Amer. Soc. of Anim. Sci., Raleigh, NC, USA, on July 29, 1981.

⁴ Dept. of Food Sci.