Effect of kappa-casein and beta-lactoglobulin loci on milk production traits of Holstein bulls

The use of molecular information has increased genetic gain especially in breeds with long generation interval. The candidate gene approach is the most suitable method for use on natural populations. In this approach، genotypic values are measured at loci with known physiological and biochemical relationships to the phenotype of interest. In this study، the effect of polymorphisms in the -Lactoglobulin (exon 4) and -Casein (exon 4) on bull breeding values for milk، fat، and protein yield were investigated. In order to test for an association between RFLP in these loci and milk productivity، DNA from 134 Iranian Holstein bulls were extracted. The 260bp fragment for beta-Lactoglobulin and the 350bp fragment for kappa-Casein was amplified and restricted with PCR-RFLP. The frequency of A allele in BLG and KCN were 0. 325 and 0. 813، respectively. Breeding values for milk related traits (milk yield، fat، and protein yield) were estimated using the BLUP based on an animal model and AIREML algorithm. The effect of the genotypes on the breeding values for milk related traits was examined using least square methods. The effects of BLG gene polymorphism on protein yield were significant (p<. 01). The average allele substitution effect in BLG gene was 3. 25 kg for protein yield. The effect of polymorphisms in the -Lactoglobulin (exon 4) and -Casein (exon 4) on bull breeding values for milk، and fat yield were not significant (p<0. 05).