CONDITION OF THE UTERINE CERVIX IN RELATION TO CYCLE STAGE, PLASMA PROGESTERONE AND ESTRADIOL-17-BETA CONCENTRATIONS IN THE MARE

Changes in the uterine cervix of the mare are primarily regulated by progesterone and estrogens. The condition of the cervix was assessed during fertility examination of 31 mares in seasonal anestrus, of 150 mares in estrus and of 115 mares in diestrus. The determination of cycle stage was based on behaviour and ovarian and uterine criteria. The cervix was categorized according to visual and palpatory characteristics. Evaluation of the cervical state relative to plasma progesterone and estradiol-17 beta concentrations and cycle stage indicated that, on an individual mare basis, the determination of cycle stage using cervical characteristics alone is not reliable. Progesterone concentration (<1 ng/ml vs. >1 ng/ml) and the estradiol-17 beta: progesterone ratio (>5 vs. <5) were more useful as means of differentiating between estrus and diestrus than was estradiol-17 beta concentration alone. It was concluded that not only ovarian hormones, but also other factors such as the number of foals produced by the mare, may have an effect on the condition of the uterine cervix.