Fertility in Ewes Treated with Luteinizing Hormone-Releasing Factor 1

Abstract

Summary

The effect of synthetic lutenizing hormone-releasing factor (LRF) on ovulation and fertility was investigated in the cyclic ewe. Twenty ewes were given 10 mg progesterone sc daily from Day 10 through Day 19 (estrus-Day 0) of the estrous cycle. Of these, 13 were also given 50 μg synthetic LRF iv on Day 23. Serum LH levels were measured by radioimmunoassay on blood samples taken on Days 22 and 23. Ewes which did not exhibit estrus were mated 24 hr after LRF; the rest were mated 12 hr after onset of estrus. Ova were examined for cleavage 72 hr after mating. In the control group, 6 of 7 ewes ovulated (86%) and 4 of 6 recovered ova (67%) were fertilized. Estrus occurred in nine of 13 ewes before or on the day of LRF administration. Eight of these ovulated (89%) with 5 of 8 oya fertilized (63%). Of the 4 ewes which did not exhibit estrus 3 ovulated (75%) but no ova were fertilized. Another 10 ewes were given 3 mg progesterone daily from Day 10 through Day 19 and 50 μg LRF on Day 21. They were mated 24 hr after LRF administration and ova were examined 72 hr later. Of 3 ewes exhibting estrus immediately after LRF, one had fertilized and 2 had unfertilized ova. Each of 7 ewes not showing estrus ovulated, but none of these ova were fertilized. All fertilized ova were replaced into the uterus and continued development to term. The data indicate that although ovulation can be induced by LRF, fertility of the released ova may be impaired if ovulation is induced prematurely.