Semen evaluation for verification of azoospermia after vasectomy in chimpanzees (Pan troglodytes)

Standards for the reproductive management of captive chimpanzees stipulate that chimpanzees admitted into the National Chimpanzee Sanctuary System must undergo vasectomy followed by laboratory confirmation of azoospermia. In light of the observations of ourselves and others, we questioned whether azoospermia is a necessary indicator of successful vasectomy. Therefore, the objectives of the present study were to assess how much time is required between vasectomy and semen evaluation for azoospermia to be reached and to determine the percentage of vasectomized chimpanzees that actually are azoospermic. The study population comprised 39 adult male chimpanzees that underwent vasectomy and subsequent semen examination at 0.5 to 24 mo afterward. Overall, spermatozoa were found in the semen of at least 1 chimpanzee in almost every month in which animals were evaluated. Of the animals evaluated repeatedly after vasectomy, 20% had no sperm at any examination, 60% were azoospermic then positive during at least 1 subsequent examination, 13.3% were positive at least once and then azoospermic, and 6.7% were positive at every examination. After 0.5 mo postvasectomy, all sperm observed were nonmotile. The results suggest that azoospermia is not a necessary indicator of successful vasectomy.