A comparison of two dosages of fluorogestone acetate in pessaries on the quality of embryos recovered from superovulated ewes

Abstract

The effect of synchronizing estrus using two dosages of progestagen (30- or 40-mg fluorogestone acetate; FGA) pessaries on the quantity and quality of embryos produced following superovulation with pregnant mare serum gonadotropin (PMSG) was investigated using 19 donor ewes. The viability of ova recovered on Day 3 or 6 after insemination was investigated by transfer to synchronized recipient ewes. The ovulation rates and proportions of embryos recovered were not significantly affected by the level of progestagen priming or the day of embryo recovery, although overall the recovery rate was lower at 3 days after insemination than at 6 days (46.5 vs 71.3%). The level of progestagen priming caused no apparent difference in the quality of ova recovered on Day 3, but on Day 6 a significantly smaller proportion of the ova were of transferable quality when recovered from donors treated with the 30-mg FGA pessary compared with the 40-mg pessary (43.3 vs 87.5%). Embryos recovered on Day 6 from the donor ewes treated with 30-mg FGA pessaries exhibited a wider spread in the stages of development than those collected from ewes treated with 40-mg FGA pessaries. Results for the transfer of embryos 3 days after insemination were consistent with the hypothesis that the level of progestagen priming prior to superovulation affects embryo viability, the mean survival rate for the 3-day embryos being 58.3 and 75% for the 30- and 40-mg FGA treatments, respectively.