[Similarity in the incidence of mastitis in the daughters of related bulls].

The overall prevalence of mastitis in the cow population, selected with respect to sire relatedness, was 12%. As positive for mastitis the cows with positive bacteriological findings in milk were considered. In order to objectify the evaluation by regarding the lactation number achieved, the index of morbidity In was introduced (In = number of positive findings/lactation achieved). Using this index, the groups of halfsisters--daughters of bulls and their sons--were compared and within-group variances were calculated. Differences in In between the groups of unrelated bulls were highly significant (P less than 0.01). In the progeny of sons of the same bull no significant differences were found. This indicates the role of genotype in the susceptibility to mastitis. Mean In value was 0.04 and 0.05 for the progeny of Czech Pied and Friesian breed, resp. No marked differences were observed between the groups of daughters of related bulls. The portion of Staphylococcus infections in the total number of positive findings was higher in the progeny of Friesian bulls (26.3 and 19.8% for the first and the second generation, resp.) than in the progeny of Czech Pied bulls (16.2 and 16.5% for the first and the second generation, resp.).