Analysis of the quality of sperm production in dairy bulls of different ages

Studying the qualitative changes in the sperm of young bulls that occur during the period of physiological maturation allows for a more accurate prediction of their reproductive abilities. Purpose. To analyze the age-related dynamics of the qualitative (physical and biochemical) indicators of the sperm of young breeding dairy bulls. Materials and methods. The work was carried out at the breeding enterprise of JSC Nevskoye (St. Petersburg) in the period from November 2023 to April 2025. Groups of Holstein (n=25) and Ayrshire (n=12) bulls aged from 11 to 24 months were formed. Sperm production was obtained 2-3 times a week from conditionally healthy animals. Results . The dynamics of sperm production indicators in dairy bulls aged 12 to 24 months showed the nature of reproductive function formation. There was a large variability in the average indicators, which is associated with the instability of spermatogenesis and the individual influence of the bull. The volume of the ejaculate increased by 1.8 times (p<0.05) in Holstein bulls and by 1.5 times (p<0.05) in Ayrshire bulls during the study period. The progressive mobility rate for Holstein bulls was 60–67 % at 13 months of age, while it was 36.2-49.7 % for Ayrshire bulls at 12-18 months of age. The quantitative indicator of spermatozoa in the ejaculate up to 14 months of age in all bulls was 3 billion/ml, further had a tendency to grow and after 19-20 months was significantly higher (p<0,05). It has been established that the period in which the produced ejaculate is suitable for cryopreservation in Holstein bulls is 14-15 months, in Ayrshire bulls it occurs somewhat later - in 19-20 months. With age, there is a tendency for the number of frozen quality sperm doses to increase - 51..54 at 12-13 months and 91..97 at 21-22 months. At the same time, the proportion of discarded ejaculate decreases - 46-57 % and 29-34 %, respectively, during the same periods. For Holstein bulls, the influence of the "age" factor was only observed on the average volume of the ejaculate (p<0.05). For the Ayrshire breed of bulls, the factor "age" had a highly significant effect on the volume of the ejaculate, the concentration of spermatozoa, and the activity of the sperm (p<0.001).