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 matu ration 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 cel l mass (ICM), pattern of protein synthesis, and ability to establish pregna ncy 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 +/- S D) 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 c ell number ratio (cow= 0.27 +/- 11, calf= 0.25 +/- 12). No differences were noted in the constitutive and the neosynthetic protein profiles between co w and calf embryos obtained in vitro. The results of embryo transfer, showe d 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% f or cow embryos. In conclusion, it would seem that embryos originating from calf oocytes are less capable of establishing pregnancies than embryos obta ined from adult oocytes, althrough this difference was not significant. Thi s low viability cannot be explained by differences in cell number or by the protein profiles identified between these 2 groups of embryos. (C) 1998 by Elsevier Science Inc.