Variability and heritability of milk traits of holstein - frisian bull dams and their progeny

The research was performed on Holstein-Friesian and Black and White bull dams reared on five farms of Agricultural Corporation of Belgrade - PKB. The study included 575 lactations of cows selected as bull dams and their progeny calved in the period from 2007 - 2014 and represent progeny of 24 bulls. The following dairy traits were analysed in a standard lactation (305 days): milk yield (kg) - MY, milk fat content (%) - % MF, milk fat yield (kg) - MFY, protein content (%) - % PC and protein yield (kg) - PY. Holstein-Friesian bull dams and their progeny, in standard lactation, produced on average 9239.84 +/- 1607.64 kg of milk, with a milk fat content of 3.44 +/- 0.20 and protein content of 3.21 +/- 0.12. The impact of bull - sire, year of birth, lactation order, farm, year and calving season was present at different levels of statistical significance on yield traits, while the genetic group had no influence on any of the milk traits. Bull sire, year of birth, lactation order and calving season did not influence the variability of milk fat and protein content. Heritability of observed milk traits was medium to low. The content of milk fat and protein had the lowest values of heritability, 0.014, and 0.024, respectively. The heritability of milk yield, milk fat yield and protein yield was 0.293, 0.319 and 0.273, respectively