Relationship between genetic polymorphism of κ-casein and quantitative milk yield traits in cattle breeds and crossbreds in Serbia

The quality and yield of milk, and therefore of dairy products as well, depends directly on their protein composition. Milk gene proteins represent structural locuses that are functionally associated with milk production. In cattle selection a special importance is attached to the variability of kappa casein (κ-CN) as one of the four casein milk proteins. Genotypes of 21 Simmental breed cows, 20 crossbred cows obtained by crossing of Simmental and Red Holstein breed, and 25 cows of autochthonous Busha breed were determined for kappa casein by restriction fragment length polymorphism analysis (PCR- RFLP) of amplified DNA. The κ-CN genotype frequencies for Simmental breed were: 42.8; 47.6 and 9.6 % for AA, and BB genotype, for crossbreds: 75.0; 25.0 and 0.0% and for Busha individuals: 41.7; 50.0 and 8.3 %, respectively. Frequencies of A and B alleles, assessed on the basis of genotypic frequencies were 0.667 and 0.333 for Simmental breed, 0.875 and 0.125 for crossbreds and 0.667 and 0.333 for autochthonous Busha cattle breed, respectively. For confirming the phenotypic variability of milk yield in standard lactation, yield of milk fat and the content of milk fat per κ-CN genotypes within breeds observed the fixed model which included the breed effect, lactation in order and effect of κ-CN genotype (AA, and BB) was used. The κ-CN genotype statistically significantly (p ≤0.05) influenced milk yield and highly significantly (p ≤0.01) milk fat yield, while the content of milk fat was not statistically significantly (p>0.05) influenced in examined animals.