To estimategenetic parameters for milk production traits, test day records of first lactation Holstein cows during the years 2001 to 2009 Mahdasht Sari was collected, was used. The data examined in this study included 9782 test day records of 1140 holstein cows in milk More
To estimategenetic parameters for milk production traits, test day records of first lactation Holstein cows during the years 2001 to 2009 Mahdasht Sari was collected, was used. The data examined in this study included 9782 test day records of 1140 holstein cows in milk and meat complex was Mahdasht Sari. Analysis of test day records was performed using the software DFREML. Fixed and random regression was according to the modelLegendrepolynomialsfrom days oflactation. The model fitted well with the 3 degree for genetic and environmental permanent factors. The minimum level of heritability (0.039) was related to,early lactation period and its value increased in late lactation and at about the ninth month of lactation to reach peak levels (0.280). Phenotypic variance of milk production traits during lactation are not the same and its value was higher in early and late lactation period. The maximum amount of genetic variance in the tenth month was 18.750 and the minimum in the early lactation period was 2.360.Residual variances for milk production trait were constant. The maximum amount of genetic and phenotypic correlations between adjacent days in milk was observed and correlated to the amount of this increase was reduced between days of lactation. Using test day records, increased accuracy of estimating genetic parameters.
Manuscript profile
