Fertilization and development of mouse eggs injected under the zona pellucida with single spermatozoa treated to induce the acrosome reaction

Mouse spermatozoa were capacitated and acrosome reacted by incubation for 30 min to 6 h in modified Tyrode's medium (T6) and in cGMP. The fertilization rates of eggs microin‐jected with a spermatozoon from samples incubated for 30 min, 2 h, and 6 h in T6 and in cGMP were 36%, 34%, 29%, and 43%, respectively. These rates were not correlated to the percentage of acrosome‐reacted spermatozoa identified after these treatments. The lack of association could be explained by the selection of an increased proportion of acrosomc‐reacted spermatozoa actually used for microinjection, particularly in samples incubated for 30 min and 2 h in T6. Both acrosome‐intact and acrosome‐reacted spermatozoa were identified under the zona in the eggs which failed to fertilize. Fertilized eggs developed at very high rates to the blastocyst stage in vitro.