Estrous cycle of the mare evaluated by fecal steroid metabolites

Summary The estrous cycles of four domestic mares were characterized by means of urinary estrone conjugates (E 1 C) and immunoreactive pregnanediol-like progesterone metabolites (iPdG). The urinary E 1 C concentrations were compared to fecal E 1 C concentrations, and urinary iPdG concentrations were compared to fecal iPdG and progesterone (P 4 ) concentrations, in order to evaluate the use of fecal steroids for assessment of ovarian function. Correlation coefficients for urinary steroid conjugates versus fecal steroid conjugates of P 4 ranged from r=0 to r=0.83, but fecal E 1 C, iPdG, and P 4 all paralleled the qualitative changes in ovarian endocrine function assessed by urinary steroid conjugate analysis. Fecal P 4 provided a more accurate assessment of the luteal phase than fecal iPdG. The results indicate that ovarian endocrine activity in the mare can be evaluated through the use of fecal steroids or their metabolites, and that this approach may be useful for the study of reproduction in free-roaming feral horses.