Embryo collection in prepubertal gilts and attempts to develop an improved embryo transfer technique.

Prepubertal gilts were treated with 1,500 iu equine chorionic gonadotrophin, followed 72 hours later by 500 iu human chorionic gonadotrophin (hCG), and inseminated 36 and 48 hours later. Embryos were collected at slaughter 168 hours after the hCG treatment. Blastocysts classified as 'good' or 'fair' were transferred to synchronised recipients, either by conventional surgical means or by a 'semi-endoscopic' approach, and the recipients were slaughtered four weeks later. Of 238 donor gilts, 98.4 per cent had responded with a mean (se) 23.5 (1.0) ovulations and 19.1 (1.0) ova or embryos, of which 47 per cent were considered morphologically intact and transferable. The large proportion of non-transferable embryos was not associated with the age or weight of the gilts, the season or with their housing conditions. Conventional surgical transfer of 15 to 20 (mean 17.4) blastocysts to synchronised recipients yielded 88 percent (14 of 16) pregnancies with between seven and 14 (mean 8.2) viable fetuses, and an embryo survival rate of 47 per cent in the pregnant recipients and 41 per cent in all the recipients. The corresponding data for the semi-endoscopic transfers were 16 to 20 (mean 17.7) blastocysts transferred, 47 per cent (eight of 17) pregnancies, four to 12 (mean 7.3) viable fetuses per pregnant recipient and an embryo survival rate of 41 per cent in the pregnant recipients and 19 per cent in all the recipients. Significantly fewer of these recipients became pregnant and a significantly smaller proportion of the embryos survived (P<0.05).