Abstract The polymorphisms and their combination of κ–casein gene and their correlation to milk performance traits in Chinese Holstein cattle were investigated for the purpose of providing molecular maker information to facilitate the breeding efficiency of high milk protein and milk fat. PCR-RFLP、CRS-PCR and Sequencing were applied to analyze the polymorphisms of two loci in κ–casein gene exon 4 and 5 in 435 Chinese Holstein cattle. Genotypic frequencies, allelic frequencies, correlation analysis between different genotypes and genotype combinations and milk performance traits were estimated. At locus T10996A, the cows with genotype TA was very significantly higher fat rate than those with genotypes AA(P < 0.01) ; with genotype TA showed higher protein rate than those with genotypes AA(P < 0.05). At locus T12980C, the cows with genotype TC was very significantly higher fat rate than TT genotype, (P < 0.01) ; with genotype TC and CC showed higher protein rate than those with genotypes TT(P < 0.05). 8 genotype combinations were found in 435 Chinese Holstein cattle，the cows with genotype combinations TTCC had the highest milk fat percentage and the third was genotype combinations TATC. The cows with genotype combinations TATC showed highe milk protein percentage than those with genotypes AATT(P < 0.05). 【Conclusion】The correlation was detected between different genotypes and genotype combinations and fat rate and protein rate at these two loci, but there was no correlation between the polymorphisms and milk yield and fat protein ratio.
