Endocrine and Body Growth Traits in Heifers Exposed to Testosterone-Propionate During Early Fetal Development2

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Abstract
This study was conducted to determine the effects of testosterone-propionate exposure during fetal development on sexual differentiation and growth rates in heifers. Ten pregnant cows were given subcutaneous injections of testosterone-propionate (250 mg/injection) every other day during d 40 to 60 of gestation. Four cows aborted after the end of testosterone treatment, while four heifers (androgenized females) and two bulls (androgenized males) were produced from the six remaining pregnant, testosterone-propionate treated cows. Calves from cows that did not receive exogenous hormone treatment were used as controls. At 8 mo of age, the androgenized heifers and control heifers and control steers were challenged with 1 mg estradiol-17β to induce a preovulatory luteinizing hormone (LH) surge. Two weeks later, pituitary responsiveness to exogenous luteinizing hormone releasing hormone (LHRH; 75 μg) was evaluated in androgenized heifers and in control heifers and control steers. To monitor growth rates, all animals were weighed at 28-d intervals from birth to 380 d of age. Androgenized females exhibited a partially masculinized phenotype as well as internal male reproductive structures. Treatment with estradiol-17β first depressed (P<.05) serum LH concentrations in all animals, then induced (P<.05) a preovulatory-like LH surge in control and androgenized females. Control steers did not (P>.05) exhibit a preovulatory-like LH surge following administration of estradiol-17β. Exogenous LHRH treatment stimulated peak LH concentrations (P<.05) to a greater extent in control and androgenized females than in control steers. Growth rates of androgenized heifers were similar to control heifers (P>.10), but were lower than those of control or androgenized males (P<.05). Results of this study show that during 40 to 60 d of gestation, in utero exposure to this dose of testosterone-propionate causes partial phenotypic masculinization of heifers. However, this treatment does not affect sexual differentiation of the bovine hypothalamic centers that regulate LH release or growth rates in androgenized females. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science