Effects of progestagens and prostaglandin analogues on ovarian function and embryo viability in sheep

Current study assessed differences in the response of sheep to estrus synchronization either by the administration of two doses of prostaglandin or by the insertion of an intravaginal progestagen sponge. The preovulatory follicular dynamics and estradiol secretion, the ovulatory response and progesterone secretion and the number and quality of embryos were studied in 27 ewes treated with two doses of 100 microgram of cloprostenol, 10 days apart, and in 29 sheep treated with progestagen sponges for 14 days. Percentage of sheep responding to the synchronization treatments with signs of estrus behaviour was similar between both groups (81.5% versus 72.4%, respectively). The use of progestagen resulted in a higher diameter of the largest follicle (6.6 +/- 0.2 versus 5.9 +/- 0.2, P < 0.05), and a lower number of small (6.7 +/- 0.3 versus 9.6 +/- 0.4, P < 0.005) and total follicles (10.3 +/- 0.3 versus 12.9 +/- 0.4, P < 0.005). However, mean plasma estradiol concentration during the follicular phase was higher in cloprostenol treated sheep (P < 0.005). The mean ovulation rate was similar in both treatments (1.7 +/- 0.2 versus 1.7 +/- 0.3), but progesterone concentration during the early luteal phase was again higher in sheep treated with cloprostenol (P < 0.05). The mean number of retrieved oocytes/embryos was very similar in both treatments (1.2 +/- 0.2 versus 1.4 +/- 0.2) and showed similar fertilization rates (70.6% versus 66.7%), but, although differences did not reach statistical significance, final viability rate was higher in cloprostenol than in progestagen treated ewes (58.9% versus 46.1%, P = 0.07). Current results give new evidences supporting the negative effects of progestagens on the functionality of ovulatory follicles and support the development of new protocols for assisted reproduction including the use of prostaglandin analogues.