The characterization of bovine embryos obtained from prepubertal calf oocytes and their viability after non surgical embryo transfer.

We have previously shown that the addition of epidermal growth factor (EGF) during in vitro maturation was capable of stimulating the cytoplasmic maturation of cow and calf oocytes. The aim of the present study was to compare calf and cow blastocysts produced in the presence of EGF in terms of total cell number and cell distribution between trophectoderm (TE) and inner cell mass (ICM), pattern of protein synthesis, and ability to establish pregnancy after embryo transfer to recipients. For all experiment, embryos at Day 7 were obtained from IVM/IVF/IVC oocytes. No significant differences were noted in total cell number (cow = 138 +/- 46 vs calf = 142 +/- 59; mean +/- SD) or ICM and TE cell number between calf (ICM = 35 +/- 19, TE = 107 +/- 52) and cow (ICM = 38 +/- 21, TE = 99 +/- 32) blastocysts, nor in the ICM/total cell number ratio (cow = 0.27 +/- 11, calf = 0.25 +/- 12). No differences were noted in the constitutive and the neosynthetic protein profiles between cow and calf embryos obtained in vitro. The results of embryo transfer, showed that there was higher pregnancy loss following transfer of calf compared with cow embryos. After Day 35, the rate of pregnancy decreases, with only 22% of calf embryos maintaining pregnancy until calving compared with 39% for cow embryos. In conclusion, it would seem that embryos originating from calf oocytes are less capable of establishing pregnancies than embryos obtained from adult oocytes, although this difference was not significant. This low viability cannot be explained by differences in cell number or by the protein profiles identified between these 2 groups of embryos.