In vivo versus in vitro produced bovine ova: similarities and differences relevant for practical application.

This present review describes some differences and similarities between bovine embryos produced in vivo and in vitro. The first part outlines the respective environments during maturation, fertilisation and early embryonic development of the two types of embryos and compares their morphological, biochemical and genomic characteristics. Results from comparative studies on embryo metabolism and gene expression reveal that most parameters are similar, but some significant differences of presumptive importance for normal development have been described. Morphologic and kinetic differences between in vitro and in vivo produced embryos are also well documented. However, improved culture conditions have been reported to minimise the differences. The second part focuses on the practical consequences of the differences in relation to embryo selection, cryopreservation, sanitary risks and pregnancy following transfer as well as normality of calves. Lower viability following transfer and increased susceptibility to cryopreservation of in vitro produced embryos is discussed. Finally and most importantly, reported evidence of increased sanitary risks and abnormal foetal development associated with in vitro produced embryos is presented.