Relationships between milk yield, quality and coagulation properties with kappa-casein (к-CN) genotypes of Bulgarian Rhodope cattle breed

Abstract

Abstract. The aim of the present study was to establish the association between different к-CN genotypes with milk yield, quality and coagulation properties in dairy cows of Bulgarian Rhodope breed. For determination of milk proteins polymorphism and its relationship with individual coagulation properties of milk and its quality, 136 milk samples from Bulgarian Rhodope dairy cows reared in 4 farms were collected. The visit to the farms and the taking of the milk samples took place between May and June 2009. Animal milk is based on daily milking on the relevant control day of the current lactation. During the morning milking, 50mL samples were collected without preservative, stored in cooling bags and analyzed in the specialized lab at the Agricultural Institute, Stara Zagora by Computerized Renneting Metter. The evaluated parameters of milk coagulation properties were: rennet coagulation time (RCT, min); curd firming time (K20, min) and curd firmness (A30, mm). Milk proteins polymorphism was identified by tissue samples collection from 136 cows. To this end, specialized pliers and marks with a vial containing desiccant were used. With this technique, the tissue sample is obtained and sealed at the time of identification of the animal. After collection, tissue samples were shipped to the University in Padova, Italy for PCR-RFLP analysis. DNA was purified using a Maxwell®16 Tissue DNA purification kit (Promega) according to the manufacturer’s instructions. Data were analyzed using descriptive statistical analysis (SYSTAT 13). The results obtained give reason to the following conclusions: The highest milk yield was established in cows from the AH genotype – 16kg, whereas the lowest value was detected in cows from the BH genotype – 12.83kg. Homozygous cows from the BB genotype produced milk with the highest fat content – 5.11%, whereas heterozygous from the BH genotype: milk with the lowest protein content – 3.16%. The cows from the AH genotypes were outlined with the lowest milk fat and protein content. The longest rennet coagulation time (RCT) was observed in АА and АН genotypes, the longest curd firming time (К20) – in genotype AH, the highest curd firmness (А30) – in the milk of cows from the AB and BB genotypes.