Gamete aging and its consequences.

This review describes primarily research performed at the University of Illinois and concerned with 1) the effect of spermatozoan age on fertility and embryonic mortality and 2) cellular changes accompanying gamete aging. Under natural conditions the aging of ova may be of far greater consequence to the reproductive performance of a species than the aging of sperm. On the other hand, under the conditions of artificial insemination of domestic animals, the aging of sperm takes on a far greater importance than under natural conditions. Evidence has been found to suggest senescence in the egg results in either failure of the defense mechanism against polyspermy or deterioration of the haploid female genome. When bull sperm are stored, an early improvement in fertility occurs and is attributed to the selective death of sperm containing aberrant chromatin or other abnormalities. On the other hand, the early improvement is followed by a decrease in fertility and an increase in embryonic mortality of fertilized eggs. These negative effects are believed to relate to a change in the genetic information contributed by the sperm.