The feasibility of sexing bovine morula stage embryos prior to embryo transfer

Sex determination of bovine morula stage embryos was possible in only 33% of embryos manipulated when 15 to 17 cells were removed for analysis. These results, in contrast to those of Moustafa $\text{et}$$\text{al}$. (1) who reported a sexing rate of 63% for bovine morulae on the basis of analyzing 8 to 10 cells, cast doubt on the practicality of sexing embryos for transfer at this developmental stage. The question thus raised was investigated by analyzing the mitotic indices of bovine, rabbit and mouse embryos. The figures obtained were in agreement with other studies and indicated that only 50% of embryos could be expected to have one of ten aspirated cells in division, and that not every metaphase spread would be suitable for sexing. It was concluded that until methods of sex determination other than chromosomal analysis are developed, the sexing of morula stage embryos is not to be recommended. It is technically more complicated and much less successful than sexing later staged embryos.