The influence of the age of cows on the variability of the fertility estimate of the semen of Holstein bulls

The article considers the dynamics of variability of fertility of the semen of Holstein bulls (n=208) during insemination of heifers and cows of the 1st calving and older for the period 2015–2022 in the Moscow region. To obtain information on the fertilization of heifers and cows after a single insemination, an array of original information data characterizing their reproductive function. To assess the breeding value of bulls, the BLUP Sire Model was used, where the evaluation year (Yeari) and the age of the inseminated cow (Lactj) were used as fixed effects. Spearman's coefficient of rank repeatability was used to determine the convergence of the ranking of bulls according to estimates of the breeding value of semen fertility. High rates of fertilization after a single insemination in heifers of the same age, regardless of the year of the study, are 64.5 ... to 83%, in cows of the 1st lactation and older - 39.4–37.2%. The lactation factor (?=57.3%, p?0.001) and unaccounted-for factors (?=27.77%) have the most significant effect on semen fertility, which is demonstrated by calculations of low rank repeatability of phenotypic assessment of semen fertility (rw= -0.06–0.09). The coincidence of the ranks of the genetic assessment is no more than 24 –27%, which indicates a high variability of the trait and indicates the expediency of a separate assessment of the fertility of bull semen on heifers of the same age and on cows of the 1st lactation and older.