INVESTIGATIONS INTO THE CONTROL OF LITTER SIZE IN SWINE .1. COMPARATIVE-STUDIES ON INVITRO DEVELOPMENT OF MEISHAN AND YORKSHIRE PREIMPLANTATION EMBRYOS

Three experiments were conducted to examine the in vitro development o f preimplantation embryos from the prolific Chinese Meishan pig. Exper iment 1 was conducted to assess whether Meishan embryos would develop in vitro and retain their viability, whereas Exp. 2 and 3 examined the developmental pattern of Meishan embryos. In all three experiments, Y orkshire embryos served as a contemporary comparison. Ovulation and em bryo recovery rates were not different between Meishan and Yorkshire g ilts. Meishan embryos cultured for 96 h were capable of establishing p regnancies. The number of cell nuclei present after 144 h of culture w as lower (P < .01) for Meishan than for Yorkshire blastocysts. Meishan preimplantation embryos exhibited a slower ( P < .02) in vitro rate o f development from the four-cell to the compact morula stage than did Yorkshire embryos. Early blastocysts from Meishan gilts, although morp hologically similar in size, contained fewer (P < .06) cells than did their counterpart Yorkshire embryos. These data demonstrate that Meish an embryos develop more slowly and contain fewer cells than do Yorkshi re embryos. This differing developmental pattern of Meishan preimplant ation embryos, if similar to that previously reported in miniature swi ne and mice, may relate to increased embryo survival.