Ovarian activity in fillies treated with anabolic steroids prior to the onset of puberty.

This study investigated the effects of zero, low (0.55), medium (1.1) and high (2.2 mg/kg LW) boldenone undecylenate on the reproductive physiology of sixteen fillies from the ages of 7 to 11 months until 2 years. Ovarian activity measured by cross-sectional area, total number of ovulations, total number of follicles and the number of large follicles (greater than 30 mm in diameter) was significantly reduced by steroid treatments. Of fillies that ovulated during the first breeding season, the age of first ovulation and the second breeding season was significantly delayed in the high dose group. Final clitoral diameters and the increase in clitoral diameter over the period of the study were significantly greater in the treated groups.