Differential cleavage rates and sex determination in bovine embryos

The purpose of this study was to determine whether a correlation between embryonic cleavage rates and sex ratios in dairy cattle could be substantiated. Embryos were collected at Day 7 after estrus following superovulation and artificial insemination. Embryos from flushings where at least two different developmental stages within the same flushing could be identified were examined. A total of 476 such embryos was transferred to recipients and 110 calves were born. The sex effect was only demonstrable in flushings yielding embryos of at least three different developmental stages. The sex ratios from this group were 32%, 58% and 62% in the slow, intermediate and fast developing groups of embryos, respectively. The deviations were not significant (P = 0.084). Only 23% of the flushings provided embryos that fell into this cathegory, which limits the use of differential cleavage rates as a sexing method, unless additional embryo culture is introduced to the technique.