Allele frequencies and genotypes of kappa casein (CSN3) and their association with chemical composition and coagulation properties of milk in Brown cattle

Abstract. The aim of the present study was to evaluate allele frequencies and genotypes of kappa casein (CSN3) and their association with milk quality and coagulation properties in Brown cattle. Milk proteins’ polymorphism was found out in 155 tissue samples from cows reared at 4 farms. The analysis of milk composition was done in the lab of the Agriculture Institute – Stara Zagora on Lactoscan ultrasound milk analyzer, whereas coagulation properties of individual milk samples were evaluated on a Computerized Renneting Metter – Polo Trade, Italy. Milk samples were obtained by milk meters. The milk was analysed within 3 hours after sample collection. Naturen Plus 215/0.8L chymosin was used, with milk coagulation activity of 215 IMCU/ml. During the study, the following parameters were studied: milk fat and protein contents (%), rennet coagulation time (RCT, min), curd firmness (а30, mm) and curd firming time (k20, min). Kappa casein (CSN3) is characterised by five genotypes – АА, АВ, ВВ, АН and ВН, the frequency of which varied within various ranges. The milk of cows with genotype AB was characterized by the highest content of fat and protein: 4.85% and 5.00%, respectively. The milk of heterozygous cows from genotype AB demonstrated the longest rennet coagulation time – 18.04 min. The animals carrying the H allele produced milk with the highest curd firmness – 37.00 mm.