[Interdependance between age, stage of lactation and occurrence of subclinical mastitis in cows]

Examined were for subclinical mastitis within the period of the first to tenth lactation 3252 cows of the Bulgarian Brown breed, 1409 cows of the Bulgarian Simmental breed, 1082 cows of the Bulgarian Red breed, 314 cows of the Iskur breed, and 1086 cows of the Black Pied breed. It was established that with advancing in age the frequency of subclinical mastitis occurrence rose. This correlation varied in different breeds. In Iskur cattle the percentage of positively reacting cows in all lactations was more than twice lower than that in the Bulgarian Brown, Simmental, and Red cows. Highest frequency of occurrence as regards the various forms of subclinical mastitis was observed in the first and second month from the beginning of lactation; in later months it was found to drop to a varying extent with the different breeds, and in the ninth and tenth month it again rose. Highest percentage of subclinical mastitis during the first lactation month was established in Bulgarian Brown cows (44%), followed by Bulgarian Simmental cows (36.88%).