Transfer of pig embryos to different uterine sites

Embryo transfer in pigs normally involves surgery. In connection with the d evelopment of nonsurgical or endoscopic transfer techniques, it is importan t to know whether the uterine site to which embryos are transferred has an effect on the success rate. In the present investigation, prepubertal donor gilts were treated with 1,500 IU of PMSG and, 72 h later, with 500 IU of h CG. Gilts were artificially inseminated 24 and 36 h after hCG injection. Em bryos at the expanded blastocyst stage were collected from donor gilts. Rec ipient gilts were treated synchronous with the donors, using 1,000 IU of PM SG followed, 72 h later, with 500 IU of hCG. After a maximum of 3 h in vitr o, embryos (n = 15 to 20, (x) over bar = 17.3) were transferred surgically to the middle of the uterine horn, to the caudal quarter of the uterine hor n, or to the uterine body. Recipients were slaughtered between 28 and 34 d after transfer. The pregnancy rate of the recipients was low when the embry os were deposited in the uterine body (12%), compared with the middle (88%) or the caudal quarter of the uterine horn (81%) (P < .01). The correspondi ng average number of viable fetuses per pregnant recipient was 8.2 in the u terine body, 5.6 in the middle, and 4.5 in the caudal quarter. Average surv ival rate of embryos after transfer to the middle of the uterine horn was 4 1% vs 29 and 3% after transfer to the caudal quarter or the uterine body, r espectively (P < .01). Hence, the uterine body seems to be an unsuitable si te for embryo transfer in pigs. These results may explain the unsatisfactor y results achieved with nonsurgical embryo transfer in the past.