SCREENING OF SOME VARIABLES INFLUENCING THE RESULTS OF EMBRYO-TRANSFER IN THE EWE .1. 5-DAY-OLD EMBRYOS

Rasa Aragonesa ewes (n=89) received 2 embryos on Day 6 of the estrous cycle (Day 0 = estrus) from 46 donors of the same breed that had been superovulated with FSH-p. The influence of several variables on fertil ity and prolificacy after transfer was studied by discriminant analysi s. Our results showed that the main variables that contributed to a hi gh fertility rate were the degree of synchrony (better outcome if dono rs come into estrus later than the recipients); Fluorogestone acetate (FGA) to estrus interval and interval from previous lambing in the rec ipients, ovulation rate of the donors and recipients (better if superi or to the mean); prolificacy of recipients in the previous lambing; an d difference in developmental stage of the pair of transferred embryos (better if inferior to the mean). The main variables affecting prolif icacy were the ovulation rate and weight of the donors and progesteron e concentrations of the recipients (better if lower than the mean); ag e of the donors and difference in progesterone concentrations between donors minus those of the recipients (better if higher than the mean). The percentage of ewes correctly classified into lambing or not lambi ng status was 73% (P<0.001) and that of the ewes correctly classified as lambing 1 or 2 lambs was 81.8% (P<0.001). Whether or not the criter ia we have established for optimum transfer results are applicable to conditions other than our own still needs to be confirmed.