Glucose controls sex-related growth rate differences of bovine embryos produced in vitro

The objective of this study was to determine whether the presence of glucose in the culture medium causes more growth of male embryos than of female embryos in cows. Oocytes matured and fertilized in vitro were cultured from 24 to 48 h after insemination in CR1aa medium with or without 5.56 mmol glucose l-1. At the end of culture the mean numbers of cells of the cleaved embryos were 5.07 (+/- 0.16) in glucose-free medium and 5.29 (+/- 0.17) in medium with glucose (P = 0.86). Without glucose in the medium, the least square mean was 0.22 cells higher in males than in females. This difference was not significant (P = 0.44). However, in the presence of glucose this difference was 1.25 cells in favour of males (P = 0.0001). The possibility that the sex difference is linked with growth stimulating effects of oxygen radicals is discussed.