Material and methods. The material has been collected from 16 cats of different ages in winter and summer periods in Voronezh veterinary clinics while animals being sterilized. The testicles were fixed in Shtiva’s liquid and Buen’s liquid. The material was poured into paraffin and a series of paraffin sections 4–5 μm thick were prepared. Sections were stained with hematoxylin and eosin, iron hematoxylin, Heidengain azane, trichrome-PAS reaction and tetrachrome-PAS reaction. By means of a helical eyepiece-micrometer, the diameter of the testicles tubules and the epididymis (50 measurements for each animal) were measured. To determine the effectiveness of spermatogenesis at an increase in 900 times, the number of first-order spermatocytes in the zigotene and pachitene stage, early spermatid (50 canals for each animal) was estimated. The normality of the distribution was determined using the Kolmogorov–Smirnov test and the Lilliefors adjustment. The measurement results were processed using the nonparametric Mann–Whitney U-criteria. Changes at Р<0.05 were considered statistically significant.

Results. The maximum diameter of the testicular tubules and the canal of the epididymis was found in animals at two years of age. These parameters in cats at the age of 8 years are reduced by 29.2%, and by17.0%, respectively. Comparing the number of dying cells in old and young animals, it can be noted that in cats at the age of 8 years the number of dying spermatids increases, while spermatogenesis efficiency decrease is statistically significant (by 19.1%).