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.