Morphological development and sex of bovine in vitro-fertilized embryos

Bovine in vitro-fertilized embryos at the blastocyst stage were collected at days 7, 8, and 10 postinsemination and sex was determined via the polymerase chain reaction (PCR) to compare the embryonic development with the sex of the embryos. The percentages of males (sex ratio) after division of the embryos into three developmental groups were 68%, 48%, and 35% in the fast, intermediate, and slow groups, respectively (P = 0.014). The percentages of males on days 7, 8, and 10 were 60%, 40% and 33%, respectively (P = 0.043). The average sex ratio for the whole material was 50%. It is thus concluded that male bovine preimplantation embryos develop faster than female embryos.