Variable development of superovulated bovine embryos between day 6 and day 12

The relations between the morphological aspect of superovulated embryos at a given day of recovery and their viability in vitro were studied in order to compose a test for estimating embryo quality. The observation of 994 embryos produced by 100 donors showed that at each day of recovery, from D 6 to D 10, the embryos were distributed into at least four classes according to morphological aspect. At D 11 and D 12 more than 95 p.100 of them were divided into only two classes : abnormal and hatched blastocysts. When they were in the zona pellucida on the day of recovery, 60 p. 100 or more of the apparently normal embryos hatched after culture in vitro. 26 p. 100 or less hatched in vitro when development was apparently retarded, and none of those having an abnormal aspect, according to our criteria, hatched. When they were already hatched from the zona pellucida at recovery, 80 p. 100 of the embryos showed an increase in size after 24 hrs. of culture in vitro. The percentage of normal embryos decreased from D 6 to D 7, and then remained stable until at least D 10. The percentage of retarded embryos increased from D 6 to D 7 and then decreased. A few retarded embryos were visible at days 11 and 12. The percentage of degenerate embryos increased from D 7 to D 8 and remained stable afterwards. The proportion of donors with more than 50 p. 100 of degenerate embryos increased from D 6 to D 12. The relation with development in vivo after transplantation has been discussed.