Calculation of adjustment factors for standardizing lactations to mature age and 305-day and estimation of heritability and repeatability of standardized milk yield of simmental cattle reared on Kazova State Farm

Abstract

Adjustment factors of lactation milk yield to mature age and 305-day were calculated and heritability and repeatability of milk yield were estimated for Simmental cows reared on Kazova State Farm. A total of 1549 lactation records of Simmental cows reared on Kazova State Farm between 1992 and 2002 were used. The factors for standardizing incomplete lactations to 305-day were estimated by taking 7 calving age groups into consideration (2, 3, 4, 5, 6-8, 9 and 10 years of age and older). The factors for standardizing to mature equivalent estimated by polynomial regression are between the 24(th) and 143(rd) month and older. The repeatability of milk yield was estimated as 0.44 +/- 0.028 using intra-class correlation. Heritability of milk yield was estimated using paternal half-sib correlation. Heritability of milk yield for all lactations was estimated as 0.24 +/- 0.08. Heritability for first lactation was estimated as 0.30 +/- 0.154.