Characterization of the cervix in cycling mares using ultrasound

Abstract

Fourteen mares, 6 Arabians and 8 Thoroughbreds, were used to examine the efficacy of ultrasound for the evaluation of the mare's cervix during the estrous cycle. Within a 125-day period during the physiologic breeding season, mares were examined by palpation and ultrasound at 48h intervals during diestrus and proestrus beginning on day 10 of the estrous cycle, and at 24-h intervals during the periovulatory period. Mares were bred by artificial insemination at 48-h intervals until ovulation was detected. During each examination, uterine tone and cervical characteristics were determined by palpation. Ultrasound was used to evaluate the reproductive tract, noting the presence of uterine fluid and/or edema, follicular status, and cervical characteristics. The ultrasound exam of the cervix included observations of diameter and discernability of the endometrial-myometrial junction. A five-point cervical score was developed based on observed characteristics. A photograph of each cervical monographic image was taken and analyzed for reflectance by video densitometry. Blood was collected on days 0, 6, and 12 post-ovulation and analyzed for progesterone. Cervical relaxation was found to be greatest on the day before ovulation while the uterus was found to be most flaccid on the day of ovulation. Cervical evaluation by palpation and by cervical score were highly correlated (r = .86). Cervical diameter was best correlated with the ultrasound rating system (cervical score) (r = .68) and cervical density was found to have its greatest correlation with cervical diameter (r = .46). A 71% pregnancy rate (10 of 14) was achieved. Mean progesterone concentrations for days 0, 6, and 12 were.24,13.15 and 11.41 ng/ ml, respectively. Two non-pregnant mares had progesterone concentrations below.30 ng/ml on day 12 which was accompanied by loss of cervical tone and changes in the monographic appearance of the cervix. The mean cervical diameter for pregnant and non-pregnant mares on day 12 postovulation was 2.85 cm and 3.43 cm, respectively. In this study, cervical echography was shown to be a useful adjunct to cervical assessment by palpation in cycling mares.