Influence of age and mode of use of bulls on their daughters' milk yield.

摘要

Chemical composition, somatic cell count and daily milk yield of 13791 cows: daughters of different groups of bulls (AI proven and young local bulls, foreign bulls and bulls used in natural service) of different age classes, were compared. Milk yield and protein content in milk of foreign bulls' daughters were higher than that of cows by approved national bulls. Daughters of young tested bulls produced milk containing more fat and less somatic cells than daughters of bulls used in natural service. Milk yield increased together with the decreasing age of sires. In the case of cows from national approved bulls and foreign bulls (imported semen) this tendency was accompanied by the decrease of fat content in milk. The fat and protein contents in the milk of cows by the oldest group of proven local bulls were higher than in milk of the oldest foreign bulls' daughters. Milk of cows by younger age classes of foreign bulls contained more fat and protein than milk of cows by younger national approved bulls. In the case of protein content, differences in favour of foreign bulls' daughters increased together with the decreasing bull age..