FOLLICULAR ACTIVITY AND OVULATION REGULATED BY EXOGENOUS PROGESTAGEN AND PMSG IN ANESTROUS EWES

Follicular dynamics and ovulation were compared in 3 groups of anestro us ewes: those treated with medroxyprogesterone acetate (MAP) sponges for 12 d, then with 750 IU PMSG at the time of sponge removal (P4+PMSG , n=6), or PMSG alone (n=6) and untreated controls (n=6). Waves of fol licular activity were observed in all the animals. In the P4+PMSG trea tment group, MAP priming permitted more ovulatory follicles (P<0.001) to be recruited without changing follicle growth rate; MAP priming als o delayed the time of ovulation (P<0.001) and the time of the LH surge (P<0.01), which allowed for an increase in the size of ovulatory foll icles (P<0.05). Ovulation also resulted in normal luteal function afte r P4+PMSG (P<0.01) but not after PMSG alone, since premature luteal re gression occurred in 80% of the cases and was related to the presence of follicles >4 mm when P4 levels were <1 ng/mL on the day following o vulation. The results showed that MAP priming increased the ovulation rate by increasing the number of follicles that responded to PMSG. (C) 1998 by Elsevier Science Inc.