Short communication: Carora cattle show high variability in alpha(s1)-casein.

The objective of this study was to analyze the genetic variability of milk proteins of the Carora, a shorthorned Bos taurus cattle breed in Venezuela and in other Southern American countries that is primarily used for milk production. A total of 184 individual milk samples were collected from Carora cattle in 5 herds in Venezuela. The milk protein genes alpha(s1)-casein (CN) (CSN1S1), beta-CN (CSN2), kappa-CN (CSN3), and beta-lactoglobulin (LGB) were typed at the protein level by isoelectrofocusing. It was necessary to further analyze CSN1S1 at the DNA level by a PCR-based method to distinguish CSN1S1G from B. Increased variation was found in particular at the CSN1S1 gene, where 4 variants were identified. The predominant variant was CSN1S1B (frequency = 0.8). The second most common CSN1S1 variant was CSN1S1G (0.101), followed by CSN1S1C (0.082). Moreover, a new isoelectrofocusing pattern was identified, which may result from a novel CSN1S1 variant, named CSN1S1I, migrating at an intermediate position between CSN1S1B and CSN1S1C. Six cows carried the variant at the heterozygous condition. For the other loci, predominance of CSN2A2 (0.764), CSN3B (0.609), and LGBB (0.592) was observed. Haplotype frequencies (AF) at the CSN1S1-CSN2-CSN3 complex were also estimated by taking association into account. Only 7 haplotypes showed AF values >0.05, accounting for a cumulative frequency of 0.944. The predominant haplotype was B-A2-B (frequency = 0.418), followed by B-A2-A (0.213). The occurrence of the G variant is at a rather high frequency, which is of interest for selection within the Carora breed because of the negative association of this variant with the synthesis of the specific protein. From a cheese-making point of view, this variant is associated with improved milk-clotting parameters but is negatively associated with cheese ripening. Thus, milk protein typing should be routinely carried out in the breed, with particular emphasis on using a DNA test to detect the CSN1SG variant. The CSN1SG allele is likely to have descended from the Brown Swiss, which contributed to the Carora breed and also carries this allele.