Effect of k-casein and ß-lactoglobulin genotypes on the milk rennet coagulation properties
Institute of Veterinary Medicine and Animal Science, Estonian Agricultural University, Kreutzwaldi 1, 51014 Tartu, Estonia; e-mail: email@example.com
Purpose of this study was to find connections between milk renneting properties of dairy breeds in Estonia and the genetic variants of k-casein and ß-lactoglobulin. Milk (n = 2161) and blood (n = 87) samples were taken from Põlula Research Farm where all dairy cattle breeds are represented: Estonian Holstein (EHF) – 45 cows, Red-and-White Holstein (RHF) – 12 cows, Estonian Red (EPK) – 26 cows and Estonian Native (EN) – 4 cows) raised in Estonia. Milk samples were analysed for fat, protein, calcium, and phosphorus contents, somatic cell count, and rennet coagulation parameters. Rennet coagulation properties of milk from cows of four experimental groups were higher in EK group. No noncoagulated milk samples were observed in this group. Estonian Red breed has the second-best rennet coagulation properties of milk. Percentage of noncoagulated milk samples in the group of EPK (3.6%) was lower than in the groups of EHF and RHF (percentage of noncoagulated milk samples 5.0% and 7.7%, respectively). All measured rennet coagulation parameters were significantly better for the k-casein BB and worse for the k-casein AA genotype. k-Cn BB exhibited also the lowest percentage of noncoagulated milk samples and samples that did not reach K20 30 min after enzyme addition. ß-Lg genotypes had no significant effect on milk rennet coagulation parameters, but it was possible to observe tendencies that milk rennet coagulation time was the shortest and the percentages of noncoagulated milk samples and samples with poor coagulation properties (NK20) were lower for the ß-Lg AA genotype. Better milk rennet coagulation properties among native breeds are explicable with a higher frequency of k-Cn B allele. The frequency of k-Cn B allele has been decreased among Estonian Holstein cows.