Serrated granulosa and other discrete ultrasound indicators of impending ovulation in mares

The incidence of discrete structural changes in the preovulatory follicle as ovulation approaches was studied sequentially by ultrasonography. Examinations were done every 12 hours in 27 mares, beginning when the follicle was ≥35 mm. The following discrete end points were recorded as present or absent: 1) serration of granulosa, indicated by an irregular or notched appearance; 2) decreased turgidity, indicated during transducer pressure; 3) loss of spherical shape; 4) an apex, indicated by a reduced area at one end; and 5) echoic spots floating in the antrum. When the records were examined as though scanning had been done only every 24 hours beginning at 35 mm, distinct serration was detected at the examination before ovulation in 37% of mares but not earlier. When mares were examined every 12 hours, serration was detected at the last examination in 59%. Decreased turgidity at the last 12-hour examination was detected concomitantly with serration, but was detected alone in 9% to 12% of previous examinations. Mares with serration at the last examination at 12-hour intervals were examined every hour thereafter (n = 14). Serration and decreased turgidity were present at each examination until ovulation 4.9 ± 0.7 hours later. Loss of spherical shape initially occurred less frequently than decreased turgidity, but the incidence increased from 50% to 100% during 6 to 1 hours before ovulation. The incidence of an apical area reached 100%, and echoic spots increased to 50% during the few hours before ovulation. Results indicated that serrated granulosa and the other discrete indicators were useful for predicting impending ovulation; however, optimal efficiency would require examinations every few hours.