The objective of this study was to develop a method of preparation and use of vasectomized stallions, and to test them as a factor preventing genital functional disorders in mares during training and hippodrome testing. Thoroughbred mares of English, Arabic and Akhal-Teke breeds owned by horse ranches of the Republic of Kazakhstan were used in the research. Vasectomy techniques were mastered on a slaughtering material, and then field tested on stallions. A series of experiments were set for comparative evaluation of various methods of preparation and use of a vasectomized stallion, resulting in a technique based on removing the front section of sperm ducts in the ventro-caudal portion of the scrotum. The developed method is convenient, safe, and easy to perform in field conditions. The surgery is not time consuming, and there are no postoperative complications. We found a positive effect of the vasectomized stallion on the course of the mares' oestrous cycles, on their performance during hippodrome testing, and their reproductive function. The method reduced the standing heat period, and the mares quickly recovered their performance. Thus, it decreased the time of the mares' elimination from the training schedule and had a positive effect on the performance during hippodrome testing. The use of a vasectomized stallion during training significantly predetermined the course of the mares' reproductive cycle after completion of the hippodrome testing. The results of this study are relevant to the practical needs of sport horse breeding. Horse, scrotum, heat period, prevention, sperm ductsReproduction and improving the quality of horses is one of the main objectives of the horse breeding farms. Nonpregnant mares have several sexual cycles within a specific

In the article it is noted that when the age of physiological maturity is reached, most of mares do not go hunting because of genital infantilism. The authors' studies showed that in the group where the repair filly had a systematic communication with the vasectomized stallions at 36 months of age, the reproductive apparatus was well developed, there were no signs of genital infantilism. All mares were found at the age of 36-37 months, and they became foal, at the mares of the control group at the indicated age the sexual cycles did not appear regularly, signs of genital infantilism were noted. The authors note that the vasectomized stallion provides, normal development of the reproductive sexual system of the repair mares, the full formation and manifestation of sexual cycles. The use of vasectomized stallions allows for an early effective prevention of genital infantilism and infertility in repair mares. Dosed communication of fillies with vasectomized colts and sterile coitus during sexual development promoted the physiological development of the genitals and the full manifestation of the sexual cycle.