Relationship between the maturational state of oocytes at the time of insemination and sex ratio of subsequent early bovine embryos

The effect of maturational state of bovine oocytes at the time of insemination on early embryo development and the sex ratio of developing embryos was evaluated. Early maturing oocytes were inseminated either immediately after the first polar body extrusion or insemination was delayed for 8 h. Most of the zygotes completed the first embryonic cell cycle and reached the 2-cell stage by 35 h after insemination regardless of the time of insemination. Delaying insemination enhanced the proportion of cleaving zygotes and significantly improved their development to the 8-cell stage. At the same time delaying insemination produced significantly higher proportions of male embryos. Cleavage and development to 8-cell stage was significantly impaired when oocytes were inseminated immediately after polar body formation. Sex ratio in these embryos did not differ from 1. These results suggest that oocytes' developmental ability as well as capability to process X and Y-bearing spermatozoa may be acquired at specific times during maturation. (C) 1997 by Elsevier Science Inc.