The effect of prenatal androgen exposure on sexual differentiation and postnatal growth in beef cattle

Masculinization of the female fetus by administration of androgens has been studied in domestic and many laboratory species. Research concerned with cattle has been based solely on neonatal examination of the genital structures; no studies have reported on postnatal growth and development of androgenized offspring. In the present study, pregnant cows were treated with l 7α-methyl-testosterone (MET, 250 mg/d, sq) from day 40 through 60 of gestation to induce virilization of female fetuses. Control cows received no treatment. At parturition, the phenotypic characteristics of each calf were recorded, including birth weight, ano-genital distance and the appearance of the external genitalia. Calves were weighed every 28 days, and the effects of sex and age on body weight were determined. Blood serum was obtained twice weekly from female calves beginning at ≃230 days of age. Serum was analyzed for progesterone (P₄) concentration by radioimmunoassay and the P₄ profiles were used to estimate the age at puberty and estrous cycle lengths. At 4, 8 and 12 months of age blood samples were collected every 15 min for 12 h from three male, female and androgenized female calves. Serum was analyzed for growth hormone (GH), prolactin (PRL) and thyroxine (T₄) concentrations by radioimmunoassay.

Visual examination of female calves born after MET exposure revealed that no external vulval opening was present; a penis, prepuce and scrotum had developed and gonads were not palpable in the scrotum. Mean birth weights were similar among male, untreated female and androgenized female calves, whereas weanling and yearling weights were greater (P < .07) in males and androgenized females than in untreated females. Androgen exposure did not affect the initiation or length of estrous cycles in female calves, however, puberty occurred at an earlier age (P < .05) compared with untreated heifers. Concentrations of GH in serum from androgenized female calves were generally lower than both males and untreated females, whereas concentrations of PRL and T₄ were similar to those of control female calves.