Genotypic factors of mastitis resistance in Holstein Black-and-White cattle
With an increase in the proportion of Holstein "blood", there is a tendency to decrease the frequency of udder disease. Among cows with less than 45% of the "blood" of the improving breed, 46.8% of animals are sick, while among high-blooded crossbreeds with a share of "blood" exceeding 76%, the incidence of animal diseases was 18.9%. The daughters of sick mothers get mastitis more often than the daughters of healthy cows. If cows susceptible to mastitis are removed from the herd, it is possible to increase mastitis resistance in the next generation. In the course of the research, significant differences in the incidence of cows with mastitis were established in the genealogical groups of the herd - families and lines. Among maternal families with the largest number of lactating cows belonging to them (from 5 to 13 heads), the incidence rate ranged from 0 to 71.4%. Taking into account the linear affiliation of animals, the incidence of cows in genealogical lines varied from 10% in the Annas Adema line 30587 in the Cornflower bull 761 and up to 83% in other lines in the Lukoil bull 983. Animals from the Montvik Chieftain 95679 line with a morbidity rate of 18.9%, which is significantly lower than the average for the herd, should be classified as relatively resistant. The animals of the breeding herd are the descendants of 54 bulls. In total, 10 producers were evaluated for mastitis resistance of the offspring. The incidence of cows-daughters of these bulls is not the same. The highest breeding value in terms of mastitis resistance of the offspring was possessed by the bull Deltar 1952. Among the evaluated bulls, 25% are classified as improvers on this basis, 18.7% are neutral and 56.3% are classified as degraders. It is proposed to take into account the sign of its mastic resistance in the mass breeding of highly productive Black-and-White cattle.