EFFECTS OF BETA AND KAPPA CASEIN ON BREEDING VALUES PREDICTIONS IN DAIRY CATTLE
Keywords:milk production traits, beta casein, kappa casein, BLUP
The objective of this study was to estimate the genetic parameters and breeding values for milk yield, protein yield and protein percentage in 87 crossbred dairy cattle with pedigree and production records and beta and kappa casein genotypes. The data was analyzed using three mixed model equations. The first model included fixed effects
and random effects, identifying additive and permanent environments. The second model was similar to the first model using beta (a) or kappa (b) casein genotype (single gene) effect. The third model was the same as the first model but used composite beta and kappa casein genotype (multigene) effects. Variance components and breeding values were estimated by the Restricted Maximum Likelihood (REML) method and Best Liner Unbiased Prediction (BLUP), respectively. Heritabilities of milk yield were 0.51 (model 2a) to 0.57 (model 1), protein yield 0.43 (model 3) to 0.45 (model 1), and the protein percentage ranged from 0.21 to 0.22. Of all the three models analyzed, model3 was found to be better in explaining the source of variance than the other two, based on -2logL values. Analyses from model3 (multigene) were different from model1 in which genotypes were not included. As a result, the ranking of cows, based on their breeding values, showed differences between the two models. When beta or kappa casein genotypes were included separately in the model (2a or 2b), there were no difference in the ranking of the cows for milk and protein percentage. For all three models, the ranking of cows based on their breeding values showed no differences for protein yield.