173 TRANSFER OF VITRIFIED BLASTOCYSTS FROM ONE OR TWO SUPEROVULATED LARGE WHITE HYPERPROLIFIC DONORS TO MEISHAN RECIPIENTS: REPRODUCTIVE PARAMETERS AT DAY 30 OF PREGNANCY

Abstract

The present study was designed to determine the effect of pooling embryos from two donors on the reproductive success of transfer of vitrified/warmed porcine blastocysts. Superovulated Large White hyperprolific gilts (n = 24) were used as embryo donors. Gilts were artificially inseminated 12 and 24 h after initial detection of estrus using fresh semen, and slaughtered on Days 5.5 to 6 of the estrous cycle (Day 0 = Onset of estrus). Embryos were recovered by flushing the uterine horns, and unhatched blastocysts were selected. Vitrification and warming were performed as reported previously (Berthelot et al., 2000 Cryobiology 41, 116–124). Embryo transfers were conducted in asynchronous (−24 h) Meishan gilts (n = 20). Twenty vitrified/warmed blastocysts were surgically transferred into one uterine horn. Ten recipients received embryos from one donor (group 1) and the other ten transfers were performed with mixed embryos from two donors (group 2). Pregnancy was assessed ultrasonographically at Day 25 after estrus and recipients were slaughtered five days later. The pregnancy rate from the different groups was compared using Fisher exact test. The GLM procedure of SAS was used to determine the effect of the origin of embryos (one or two donors) on the number of developed fetuses and viable fetuses at Day 30 of pregnancy. The ovulation rate was 32.5 ± 11.8 (mean ± SD). The total number of embryos collected was 634, of which 57 (9.0%), 36 (5.7%), 513 (80.9%) and 28 (4.4%), were unfertilized oocytes and degenerated embryos, morulae, unhatched blastocysts and hatched blastocysts, respectively. The ratio of collected embryos to the number of corpora lutea was 81.3%. The pregnancy rate for group 1 (70%) was not different (P > 0.05) than that for group 2 (90%). No significant differences were detected between group 1 and group 2 for in vivo embryo development (number fetuses/transferred embryos in pregnant recipients; 33.3% v. 40%) or in vivo embryo survival (number viable fetuses/transferred embryos in pregnant recipients; 27.9% v. 33.9%). However, the in vivo efficiency (number viable fetuses/total transferred embryos) was higher (P < 0.05) when transfers were performed with embryos from two donors (19.5% v. 30.5%). These results indicate that pooling embryos from two donors increases the in vivo efficiency after transfer of vitrified/warmed porcine blastocysts. This study was supported by grant from SENECA (FPI/99, Spain).