Ovulation of aged follicles does not affect embryo quality or fertility after a 14-day progestagen estrus synchronization protocol in ewes

The aim was to examine the effect of ovulation of aged follicles on embryo quality and fertility in ewes. In Experiment 1, ewes (n = 39) received a pr ostaglandin analogue on Day 6 of the cycle and then received either a proge stagen sponge from Day 6 to 20 after estrus (Single sponge) or a progestage n sponge on Day 6 that was replaced on Day 11 and 16 and removed on Day 20 (Multiple sponges). In a subgroup of ewes, the growth of ovarian follicles was characterised using ultrasonography. Fertile rams were introduced 48 ho urs after sponge, withdrawal; we slaughtered the ewes on Day 5 of pregnancy and recovered the embryos. The mean age of the ovulatory follicles was gre ater in ewes that received a single sponge compared with multiple sponges ( 8.7 +/- 0.8 days, range 4 to 14, versus 4.5 +/- 0.7 days, range 3 to 6; P<0 .05). However, the groups did not differ (P>0.05) in ovulation rate (2.4 +/ - 0.3 corporal lutea per ewe) or the proportion of good quality embryos rec overed (71 to 82%; developed to the early morula stage or further). In Expe riment 2, ewes (570 in total) received treatments similar to those in Exper iment I but were kept until lambing, Ewes that received a single sponge cam e into heat earlier (P<0.05) than those that received multiple sponges, but <greater than or equal to>97% of ewes in all groups, (P>0.05) were bred by 48 to 72 hours after ram introduction. There was no difference (P>0.05) be tween groups for the proportion of ewes that lambed to first service (80 to 86%) or the number of lambs per ewe (1.94 +/- 0.08 lambs). We conclude tha t when luteolysis occurs at the beginning of progestagen synchronisation, e wes will ovulate aged follicles, but that compared to shorter duration foll icles, these follicles produce oocytes that are equally competent to be fer tilised and develop into good quality embryos and full-term lambs. (C) 2001 by Elsevier Science Inc.