Association of polymorphism in the alpha-1-antitrypsin gene with milk production traits in Holstein dairy cows
Alpha-1-antitrypsin (A1AT) as a strong protease inhibitor plays a major role in the protection of tissues against proteolytic destruction by neutrophil elastase. Existence of this protein in the mammary gland may increase the survival of milk proteins such as lactoferrin and lysozyme. The biological role of A1AT in tissues such as the mammary gland and results from previous quantitative trait loci (QTL) studies have provoked an investigation of A1AT as a candidate gene influencing milk production traits. The present study assessed the association of a single nucleotide polymorphism (SNP) at position 5504 of the A1AT gene with 305-day milk yield, milk fat and protein percentage and somatic cell score (SCS) in 408 Iranian Holstein cows. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used for genotyping. The effect of the genotype on the traits of interest was analysed using the general linear models (GLM) procedure of SAS software. The frequencies of alleles A and B were 0.633 and 0.367, respectively, and genotypes showed a significant deviation from Hardy-Weinberg equilibrium, which can be a result of selection for milk production traits. Results of association analysis showed a significant relationship between the SNP in the A1AT gene, and fat and protein percentage. Cows of genotype AB had higher milk fat percentage than those of genotype AA. Cows with genotype AA showed a lower milk protein percentage than those carrying genotype AB. When the association of this polymorphism with fat and protein percentage is considered, the SNP could be implemented as a marker in breeding programmes for these traits.
Keywords: A1AT gene; candidate gene; mammary gland; PCR-RFLP