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Genetic Parameters of Milk Yield at Different Somatic Cell Count Levels using Multiple-Trait Random Regression in Holsteins
Genetic parameters of milk yield test day (TD) records at three levels (low, medium and high) of somatic cell counts (SCC) were estimated using multiple-trait random regression animal model using 102,315 milk TD records from 11,455 primiparous cows collected from 158 herds across different regions of Iran over a 9-year period (2002-2010) using Gibbs sampling. Predicted additive genetic and permanent environmental variances were varied among SCC levels, indicating milk yield heritabilities varied at different SCC levels. Heritabilities decreased as SCC level increased, ranging from 0.08 to 0.34 for low level, 0.06 to 0.30 for medium level, and 0.06 to 0.14 for high level. This study showed that it is possible to decompose a naturally single trait into different traits and improve the ability to model environmental effects and its possible interaction with genetic effects
Keywords:
Genetic parameters
Milk yield
Multi-trait random regression
Somatic cell count
