Morphology and fertility of guinea pig spermatozoa aged in vivo.

The morphology and fertility of spermatozoa from vasa deferentia of guinea pigs were observed following hemicastration or castration for approximately 40 days. The morphology of these aged sperm was studied from living and fixed preparations. Fertilizing ability was assayed by artificial insemination of estrous females and subsequent counting of embryos. Spermatozoa underwent morphological changes including dissociation of rouleaux, curving of tails, and loss of acrosomes; physiological changes included a decline in the number of sperm with progressive motility and increased numbers of immotile spermatozoa with time after the operations. The fertilizing capacity of spermatozoa was maintained for approximately 30 days in both groups. However, sperm from one of the hemicastrated males resulted in conception 36 days postoperation. The data suggest that the loss of motility and decline in fertilizing ability were the result of spermatozoa senescence rather than testicular androgen deficiency.