\u201cRossa Siciliana\u201d is a dairy cattle population traditionally linked to cheese production protein polymorphisms from 62 individual milk samples from 19 farms were analyzed by isoelectrofocusing. High variability was found at the CNS1S1, CSN2, CSN3, LGB and LALBA loci, while the CNS1S2 locus was monomorphic for the A allele. The casein haplotype frequencies and the occurrence of the linkage disequilibrium, taking into account the association among loci were investigated. The population was not in Hardy-Weinberg equilibrium (Chi-square=19.0, p-value=0.0407), probably due to genetic drift. Frequencies of the three allele detected at CSN1S1 locus were B (0.734), C (0.258) and D (0.008). high frequencies were found for CSN2*A2 (0.573) and CSN3*B (0.637). Whey protein showed high frequencies for LALBA*B (0.903) and LGB*B (0.815). Strong linkage disequilibrium was detected for the polymorphic casein loci CSN1S1-CSN2-CSN3. Out of the 27 possible combination from the 3x3x3 alleles considered, only four haplotypes had a frequency above 0.10. the most frequent haplotype frequency was BA2B (0.236) followed by CA2B (0.214), BA1A (0.168), BA1B (0.131), and BA2A (0.094). the CSN1S1*B variant showed an allele frequency of 0.734 and occurred in almost all haplotype combinations
