CORRELATION OF PLASMA-CONCENTRATIONS OF PROGESTERONE AND ESTRADIOL WITH ULTRASOUND CHARACTERISTICS OF THE UTERUS AND DURATION OF ESTROUS BEHAVIOR IN THE CYCLING MARE

Changes in the endometrial oedema pattern during the oestrous cycle of Dutch warmblood mares were evaluated using transrectal, linear-array ultrasonography. The uterus was examined each day and the degree of oe dema scored. Peripheral blood samples were taken daily for measurement of plasma oestradiol and progesterone concentrations. Endometrial fol ds first appeared 7 days before ovulation and peaked 24 to 48 h before ovulation. Oedema score decreased before ovulation, but there was alm ost always detectable oedema on the day of ovulation. There was no dir ect correlation between oedema and oestradiol levels, but oedema was n ot detected with progesterone above basal levels. Evaluation of endome trial oedema would seem to be a useful part of the routine pre-mating examination of mares in indicating the optimal time to mate the mare a nd providing an instant indication of basal levels of progesterone.