The aim of this study was to evaluate the direct effects of
vincristine on semen quality in dogs with
transmissible venereal tumor (TVT). We examined the semen of 17 dogs suffering from TVT during
vincristine treatment. Each animal received 0.6 mg, i.v.
vincristine sulphate per square meter of body surface, per week for 4 wk until complete regression of the
tumor. The following semen parameters were evaluated: semen volume (second fraction), sperm concentration, total spermatozoa per ejaculate, percentage of progressively motile spermatozoa, percentage of dead spermatozoa, percentage of swollen spermatozoa (hypo-osmotic swelling test) and percentage of morphologically
abnormal spermatozoa (primary and secondary defects). Semen was collected and evaluated prior to the beginning of treatment, 3 d after each
vincristine injection and 15 d after the last injection. Semen characteristics transiently deteriorated during treatment, but returned to normal 15 d later. These changes were attributed to a direct effect of
vincristine on the extragonadal spermatozoal reserves contained in the epididymis and ductus deferens. A
GnRH stimulation test was also performed after each semen collection in order to assess the function of the hypothalamic-pituitary-Leydig cell axis. No effect was noted on the above axis.