Animal Reproduction (AR)
Animal Reproduction (AR)
Original Article

Relationship between vascularity of the preovulatory follicle and establishment of pregnancy in mares

L.A. Silva, E.L. Gastal, M.O. Gastal, M.A. Beg, and O.J. Ginther

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The relationship between follicle vascularity and establishment of pregnancy was studied in 21 mares. An ovulation-inducing injection of hCG was given when the preovulatory follicle was 34.0 to 37.0 mm (Hour 0). Mares that had not ovulated by 30 h after treatment were bred once (Hour 30). Each mare ovulated by 48 h after treatment, and 14 mares became pregnant and 7 were nonpregnant. The preovulatory follicle was evaluated by B-mode and Doppler ultrasonography at Hour 0 (before treatment) and Hour 30 (before breeding). B-mode echogenicity and thickness of the stratum granulosum and prominence of the anechoic band beneath the granulosum increased in both pregnant and nonpregnant groups (hour effect, P < 0.001) with no group effect or interaction. An increase in follicle diameter and percentage of follicle circumference with colorDoppler signals was greater between Hours 0 and 30 in the pregnant group than in the nonpregnant group (interactions, P<0.001). Spectral-Doppler measurements were made at the most prominent intraovarian color signal. Decreases in resistance and pulsatility indices were greater between Hours 0 and 30 in the pregnant group than in the nonpregnant group (interactions, P < 0.05), indicating increased vascular perfusion downstream from the spectral measurement in the pregnant group. Relative peak systolic velocity and time-averaged maximum velocity of blood flow at the point of spectral assessment showed a group effect (P < 0.05; greater in pregnant group) without an hour effect or interaction. Results supported the hypothesis that greater blood flow to the preovulatory follicle is associated with higher pregnancy rate.


blood flow, follicle, mares, pregnancy rate, preovulatory follicle
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