Activation of quiescent ovaries by administration of PMSG after LH-RH analogue treatment in heifers

Abstract

The effect of pregnant mare serum gonadotrophin (PMSG) treatment on activation of quiescent ovaries was examined in heifers. Groups of thirteen, twenty and twelve heifers which showed ovulation within 2 d and corpus luteum (CL) development after injection with a luteinizing hormone releasing hormone analogue (LH-RH-A) were supplementally injected with 500 IU of PMSG (Group I); 500 IU of PMSG and 500 μg of Prostaglandin F 2α analogue (PGF 2α-A; Group II); and 500 μg of PGF 2α-A (Group III) on Day 6 after the injection of 200 μg of LH-RH-A (Day 0), respectively. Estrus appeared in 33.3 to 45.0% of the heifers of the respective groups after the treatment. Ovulation occurred at a significantly (P<0.01) higher rate in Groups I (100%) and II (90.0%) than in Group III (41.7%). The ovarian cyclic activity was initiated in all the heifers that ovulated. Plasma progesterone levels decreased significantly (P<0.05) to about 1 ng/ml on Day 8 and Day 7 in Group I and Groups II and III, respectively. Plasma estradiol-17β (E z) levels increased significantly (P<0.05), reaching a peak on Days 7 to 7.5 in Groups I and II but not in Group III. It is concluded that PMSG treatment stimulates maturation and E z secretion of a follicle, thus promoting ovulation and the onset of ovarian cyclic activity.