Frequencies Evaluation of β-Casein Gene Polymorphisms in Dairy Cows Reared in Central Italy

SIMPLE SUMMARY: Bovine milk contains several β-casein variants, with the A1 and A2 variants occurring most frequently. The presence of some variants, such as A1, B, and C, is considered a risk factor for disease in humans who consume milk. These variants are probably involved in intolerance to milk and some human diseases due to the production of a bioactive peptide with opioid activity during digestion, β-casomorphin 7 (BCM-7). In contrast, the A2 variant is not involved in pathogenetic mechanisms; thus, its presence in milk is a desirable feature. The difference between the A1 and A2 variants is a mutation at position 67 of the β-casein gene (CSN2), which causes an amino acid to change from histidine (in the A1, B, and C variants) to proline (in the A2 variant). To select dairy cows on the basis of the presence of the β-casein variant A2, allele frequencies of CSN2 variants were evaluated in Italian dairy cows reared in central Italy. The results of this study may help with the selection of animals with the β-casein gene variant A2 to produce a more digestible milk that only contains the β-casein variant A2. ABSTRACT: The majority of proteins in cow’s milk are caseins, which occur in four groups (α-s1, α-s2, β, and k) encoded by different genes (CSN1S1, CSN1S2, CSN2, and CSN3, respectively). In this study, we focused on the β-casein allele variants A1 and A2 due to their influence on milk’s technological characteristics and human health. Digestion of the β-casein variant A1 leads to the formation of β-casomorphin 7 (BCM-7), a bioactive peptide that has been suggested to be a possible cause of various human diseases and associated with low milk digestibility. The potential negative role of the β-casein variant A1 in human health has stimulated the planning of cattle breeding programs based on genetic selection to increase the frequency of the A2 variant, which is associated with increased milk digestibility. The aim of this work was to evaluate the frequencies of the different β-casein variants in Italian Holstein Friesian dairy cows from cattle farms located in central Italy to select a population of A2 homozygous animals. β-casein genotypes were identified by evaluating the presence of single nucleotide polymorphisms (SNPs) of the CSN2 gene using PCR and sequencing analysis. The frequency of the desirable β-casein variant A2 in the studied bovine population was 0.61. The frequency of the undesirable A1 variant in the studied bovine population was 0.30. The frequency of the A2 allele was higher than expected for the breed; therefore, genetic selection for the A2 variant in these animals could be achieved in a fairly short time using A2 homozygous bulls.