EN
The study was conducted on 12 male dogs (5 to 10 years of age). The animals were divided into 2 groups: the experimental one (6 tamoxifen-treated dogs) and the control one (6 clinically healthy dogs). Besides, a clinical examination evaluating the overall state of health and sexual impulse, the examination of testosterone level in the blood serum was performed as well as the examination of semen (spermatozoa concentration, percentage of dead spermatozoa, evaluation of spermatozoa morphology, and evaluation of spermatozoa cell membrane activity - HOS test). It was found that tamoxifen had a negative influence on the function of the reproductive system in the dogs and caused, already in the first week of the treatment, the worsening of most of the evaluated characteristics of the semen and later, after the second week of the treatment, it produced aspermia with the complete loss of male fertility. The loss of fertility turned out to be periodical and lasted for about 60 d. After that time, the dogs regained the ability to produce ejaculate, though of much weakened quality, but later it was gradually improving.