DEVELOPMENTAL CAPACITY OF BOVINE OOCYTES COLLECTED FROM OVARIES OF INDIVIDUAL HEIFERS AND FERTILIZED INVITRO

Bovine follicular oocytes from individual heifers (n = 49) were separately matured, fertilized with frozen-thawed spermatozoa and cultured with cumulus cells. Although there were great variations in the number (mean +/- SD = 19.1 +/- 11.9) of oocytes collected from individual heifers and the percentages of the oocytes cleaved 48 hours after insemination (mean +/- SD = 69.5 +/- 18.4) and developed to the morula stage 7 days after insemination (mean +/- SD = 10.9 +/- 10.9), there were significant correlations between the numbers of oocytes collected and cleaved (the correlation coefficient: r = 0.9336) or developed to morula stage (r = 0.6633), indicating that oocytes from different heifers have the same developmental ability after in vitro fertilization. Ten morulae and 12 blastocysts which were obtained 7 and 8 days after insemination were transferred, one by one, to each uterine horn of 11 recipients. At Day 60 of pregnancy, 8 (80%) fetuses were identified in 4 (80%) of 5 recipients into which 10 embryos were transferred at Day -1 of synchrony. However, only 3 (25%) fetuses were identified in 2 (40%) of 6 recipients into which 12 embryos were transferred at Day 0 or +1 of synchrony.