Genetic polymorphism and effect on milk production of CSN2 gene in conventional and local cattle breeds in Croatia

Abstract

Over the past three decades, the scientific and public interest has been initiated by studies in which the negative effect of milk consumption of beta-casein A1 variant has been observed on consumers’ health. The production of "A2 milk" is one of the ways to economically increase the competitiveness of small and medium-sized dairy farms. Breeders of endangered local breeds are also interested in reaffirmation through production of “A2 milk”. The aim of this study is to determine frequencies of A1 and A2 variants of beta-casein in three commercial and three local breeds of cattle in Croatia, and their relationship with production indicators of commercial breeds in the first three lactations. The genomic DNA was extracted from hair by using a commercial kit, used for determination of CSN2 genotypes by means of PCRRFLP method. Data for milk yield and chemical composition were provided by the central database. The dominant presence of A2 variant beta-casein in the investigated cattle breeds (0.650-0.758) and the increase in the frequency of A2 beta-casein in the population of Simmental and Istrian cattle were determined. The association of A2A2 and A1A1 genotypes of beta-casein with lactation production and milk fat content in the first and second lactation was observed (p <0.05). The dominance of the A2 allelic variation of beta-casein makes the researched conventional and local breeds suitable for the production of "A2 milk. The breeding extension of A2 allelic variation of beta-casein within local breeds of cattle should be carried out carefully not to lose part of the existing genetic variability.