SHORT-TERM CULTURE OF OVINE EMBRYOS MODIFIES FETAL MYOGENESIS

Certain reproductive techniques culture embryos in vitro; however, lit tle is known about the impact of culture on fetal growth. Coculture of day 1 ovine zygotes on a bovine granulosa cell layer to blastocysts f ollowed by transfer to synchronous recipients increased fetal weight b y 11 and 40% at days 61 and 125, respectively, compared with the trans fer of in vivo-produced blastocysts. Plantaris muscle weights were inc reased by 40% in cultured fetuses at day 125. Examination of myogenesi s in plantaris muscle showed that primary fiber number was unchanged a t day 61 by culture but that primary fiber area was increased signific antly by 15 and 25% at days 61 and 125, respectively; secondary fiber area was increased by 40% at day 125 by culture, and the ratio of seco ndary to primary fiber numbers was 18-20% greater in the cultured grou ps compared with the controls at days 61 and 125. The results show tha t coculture of preimplantation embryos may alter myogenic programming. These changes may contribute to the abnormally large muscles observed in oversize fetuses.