THE EFFECT OF ESTRADIOL AND TESTOSTERONE INJECTIONS AND THYROIDECTOMY ON MUSCLE FIBRE DIAMETERS AND LIVE WEIGHT GAIN IN YEARLING SHEEP

Abstract

In this study effects of estradiol and testosterone injections and thyroidectomy on muscle fibre diameters of ewe and wether yearlings were determined. Forty-eight sheep, half of which were ewes and half wethers, were subdivided into estradiol, testosterone, and control groups containing equal numbers of each sex. Half of the animals within each sex group and treatment group were thyroidectomized. Biweekly rates of intramuscular injection of estradiol and testosterone were 5 mg. and 175 mg., respectively. All animals received the same amount of feed per day throughout a 195-day experimental period.Live weight gain, carcass weight, and percentage dry matter of m. longissimus dorsi tissue were not influenced significantly by hormone injection, thyroidectomy, or sex. Estradiol injections significantly increased (p <.01) muscle fibre diameters of thyroidectomized ewes and wethers but the animals with thyroids were unaffected. Testosterone injections failed to affect muscle fibre diameters. Differences in muscle fibre diameters could not be explained by differences in percentage moisture content of muscle tissue.