Genetic Evaluation Of Milk Production Traits Of Holstein In Shandong Based On Random Regression Test-Day Model

Variance component and genetic parameters were estimated using historical data from Holstein in Shandong by random regression test day model for six milk production traits that includes milk yield,milk fat yield,milk protein yield,milk fat percent,milk protein percent and somatic cell score,utilizing software DMU(V6.0 R5.2).Data included 176,131 cows with2,535,913 DHI records from first to third parity and 572,035 pedigree records.The fixed effects in the model were herd test day and calving age,the random effects were additive genetic and permanent environmental effects,and the sub-model was a LP4 fit regression.Data set A and data set B are obtained by filtering the data with different standards,the DMUAI module was used to estimate variance components and genetic parameters for data set A.The variance components estimated for data set A that used as a priori values,and the DMU4 module was used to estimate breeding values for individuals in data set B.Genetic trends of milk production traits for Holstein population in Shandong were analyzed to evaluate the efficiency of genetic improvement strategy.According to estimated breeding values and their reliability,bulls and cows who were ranked,and excellent individuals could be selected to form the herd.The study will provide a theoretical basis for establishing a traditional genetic evaluation system for Holstein in Shandong.The results of this study are as follows:(1)5-305 d heritability of milk yield for first to third parity was 0.24,0.15 and 0.12;milk fat percent for first to third parity was 0.43,0.36 and 0.31;milk protein percent first to third parity was 0.55,0.43 and 0.41;milk fat yield for first to third parity was 0.19,0.14 and 0.10;milk protein yield was 0.20,0.14 and 0.10;somatic cell score for first to third parity was 0.11,0.10 and 0.09.(2)The annual mean genetic progress of estimated breeding values for milk yield,milk fat yield,milk protein yield,milk fat percent,milk protein percent and somatic cell score for bulls during 2006-2016 were 11.15 kg,0.38 kg,0.44 kg,0.0018%,0.00077% and-0.0022;The annual average genetic progress of the estimated breeding values for milk yield,milk fat yield,milk protein yield,milk fat percent,milk protein percent and somatic cell score for cows between2006 and 2018 were 23.84 kg,0.52 kg,0.69 kg,0.0013%,0.0023% and-0.0025.In summary,milk protein percent and milk fat percent are traits with high heritability,milk yield,milk protein yield and milk fat yield are traits with medium heritability,and somatic cell score is a trait with low heritability.The average annual genetic progress of breeding values for all traits of cows in Shandong is better than bulls,especially the milk yield of cows is 2.14 times better than the progress of bulls,which can reflect that the breeding work of dairy cattle in Shandong is steady to positive.