Molecular genetics analysis of milk protein gene polymorphism of dairy cows and breeding bulls in Latvia

D. Smiltina* and Z. Grislis

Latvia University of Life Sciences and Technologies, Faculty of Agriculture, Institute of Agrobiotechnology, Liela street 2, LV-3001 Jelgava, Latvia
*Correspondence: dace.smiltina@llu.lv

Abstract:

Milk protein is the most valuable component of milk from a dietary point of view. More than 95% of ruminants’ milk proteins are coded by six structural genes: two whey proteins (α – lactalbumin and β – lactoglobulin) and four caseins (α_S1 – and α_S2 – caseins, β – casein, κ – casein). The object of the research was the genetic polymorphisms of milk protein genes in populations of cows and breeding bulls of milk producing breeds in Latvia. The aim was to promote cow breeding in Latvia by developing and testing molecular genetics analyses for future quantity and quality analysis of the dairy cows’ population in Latvia, based on the research of genes encoding milk protein polymorphism. In methodology the molecular markers were chosen which would be suitable for characterization of polymorphism of five milk protein genes in the population of dairy cows reared in Latvia. As a genetic method chosen the Restriction Fragment Length Polymorphism (RFLP) method and most analysed alleles of milk proteins. Using data of 719 DNA samples of dairy cows, the analysis of Latvian cows’ population was carried out through six SNP of five milk protein genes: CSN1S1 c.–175A > G, CSN2 – c.4451A > C, CSN3 c.11625C > T and c.11661A > C, LAA c.15A > G and LGB c.3106T > C. The results of PCR-RFLP analysis showed, as it was expected, that all genotypes were found in the populations.

Key words:

Effect of k-casein and ß-lactoglobulin genotypes on the milk rennet coagulation properties

I. Kübarsepp, M. Henno, H. Viinalass and D. Sabre

Institute of Veterinary Medicine and Animal Science, Estonian Agricultural University, Kreutzwaldi 1, 51014 Tartu, Estonia; e-mail: ivik@eau.ee

Abstract:

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.

Key words:

genetic variants, k-casein, milk coagulation properties, milk proteins, ß-lactoglobulin