Figure 6. Activation (A) and in vitro development (B) of rat oocytes injected with heads from spermatozoa that were not heat-dried (control) or heat-dried at 50°C for 8 h and stored at 4°C for 1 week in nitrogen gas or in air.

Experiments in each treatment were repeated separately six times using 15–20 oocytes per replicate. Injected oocytes were examined 9–12 h after injection for activation, and those with two pronuclei obtained 10 h after injection were cultured and examined 24, 72, 96 and 120 h after the start of culture for 2-cell stage, ≥4-cell stage, morulae and blastocysts, respectively. The values are expressed as mean ± SEM; the total number of oocytes cultured after injection was 107, 103 and 97 for examination of activation and 98, 101 and 96 for examination of development for spermatozoa unheated (control), stored in nitrogen gas and in air after heat drying, respectively. Values with different letters within each category differ significantly (P<0.05). MPN: male pronucleus.