Impact of asynchronous ovulations on the expression of sex-dependent growth rate in bovine preimplantation embryos.
In cattle, male embryos have a faster growth rate than female embryos, and this results in alteration of the normal 1:1 sex ratio in embryos divided into three developmental groups. The fastest developed one-third are predominantly males, the slowest one-third predominantly females, and in the intermediate one-third no alteration of the sex ratio is seen, However, the deviations of the sex ratios are only 15-20% from random. These findings are compatible with the assumption that, in superovulated cows, ovulations follow a normal distribution and that, at the time of sampling at Day 7, male and female embryos differ with regard to development by 1 or 2 h. Because of this it is unlikely that larger changes in the sex ratios can be expected.
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Department of Reproduction, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
D000818:Animals; D001755:Blastocyst / Q000502:physiology*; D002417:Cattle; D005314:Embryonic and Fetal Development / Q000502:physiology*; D005260:Female; D008297:Male; D010060:Ovulation / Q000502:physiology*; D011247:Pregnancy; D012727:Sex Characteristics; D012744:Sex Ratio; D013480:Superovulation / Q000502:physiology*