Genetisk variation av betydelse för mjölkkvalitet i Rödkullerasen

Abstract: The Swedish Red Polled breed is threatened by extinction and there are only around 1100 animals left. The breed was popular in the early twentieth century, but since then the numbers have steadily decreased. The overall objective of this study was to find out whether there may be economic incentives for preserving the breed. The milk quality properties are of major importance in the production of dairy products. Therefore we would like to establish if the Swedish Red Polled breed carries favourable alleles at loci of relevance for milk quality, to potentially make the breed more interesting for milk production. The genetic variation in three milk protein genes, β-casein, κ-casein and β-lactoglobulin, and two other milk quality genes, DGAT1 and FMO3 were studied in 65 breeding bulls of the Swedish Red Polled breed. The bulls were genotyped using single-nucleotide polymorphism (SNP) analysis and pyrosequencing. The results showed that β-casein A2, κ-casein A, β-lactoglobulin B, FMO3 R and DGAT1 A were the most common variants at the respective locus in the Red Polled population. However, some bulls were carriers of the unfavourable κ-casein E allel whereas others were carrying the "shrimp" gene, which in homozygous form results in milk with a fishy taste. The "shrimp" gene had so far only been found in the SRB population and it is possible that one or several SRB bulls have transmitted the mutation to the Swedish Red Polled breed. As regards κ-casein, the B variant is preferred for cheese making because of its good renneting properties, while the E variant seems to be associated with poor renneting properties. The bulls were predominantly carrying the most favourable allele at the β-casein locus (A2) whereas the A1 and B alleles have been suspected of being involved in the disease outbreak of diabetes type 1 in individuals predisposed for the disease. Also at the β-lactoglobulin locus the bulls carried the preferred allele, B, which is associated with good processing properties. As regards the DGAT1 gene, the A variant is associated with higher yields of milk and protein but lower concentrations of fat to some extent also protein. Thus, which allele is the most favourable should differ between countries.