In-vitro production of cattle embryos: problems with pregnancies and parturition.

Using complex media containing serum and somatic cells, pregnancy rates following transfer of single, day 7 advanced-stage blastocysts approached 60%, while pregnancy rates of morulae or day 8 blastocysts were substantially lower. Pregnancies resulting from in-vitro-derived embryos were characterized by the following features: sex ratio skewed in favour of males; increased spontaneous abortion rate throughout gestation; reduced intensity of labour in recipients; and increases in birth weights, dystocias, calf mortality, and fetal abnormalities. In an attempt to improve the normality of pregnancies, a field trial was conducted within the commercial in-vitro programme at Em Tran. Following fertilization in vitro, equal numbers of zygotes were put into a Ménézo's B2-buffalo rat liver cell (B2-BRL) coculture system with (S+) or without (S-) 10% serum for the first 72 h of in-vitro culture. On day 4, all embryos were moved to fresh medium and cultured to day 7 in B2-BRL with serum. The efficiency of blastocyst production from oocytes (19.6 versus 17.8%) and the pregnancy rate at 60 days (47.8 versus 47.1%) did not differ between S+ and S-. Likewise, there was no difference between S+ and S- in the percentage of male calves (53.9 versus 54.3%), abortions (13.1 versus 11.9%), percentage of live calves (78.8 versus 81.4%), or congenital abnormalities (4.3 versus 3.3%).