β-LACTOGLOBULIN GENE POLYMORPHISM AND MILK PRODUCTION TRAITS IN SIMMENTAL CATTLE

Abstract

Genetic variants of the major milk proteins are of considerable interest in dairy cattle breeding because they may influence milk protein composition, nutritional value, coagulation properties, processing behavior, and the technological suitability of raw milk. The β-lactoglobulin gene is considered a potentially informative marker because its variants are associated with differences in the proportions of whey proteins and casein fractions. The objective of this study was to determine β-lactoglobulin allele and genotype frequencies and to descriptively compare milk production traits among genotype groups in the examined population of Simmental cattle. Materials and Methods. A total of 114 Simmental breed cows were included in the study. Genomic DNA was isolated from blood samples. Genotyping was performed by polymerase chain reaction–restriction fragment length polymorphism using the HaeIII restriction endonuclease. Genotypes were identified from combinations of restriction fragments of 153, 109, 79, and 74 bp. Allele and genotype frequencies, observed and expected heterozygosity, and the chi-square statistic for testing conformity with Hardy–Weinberg equilibrium were calculated. Based on the available production records, milk yield over a standard 305-day lactation, milk fat and protein percentages, and milk fat and protein yields were descriptively compared among genotype groups. Results. The AB genotype was the most frequent and was identified in 48.2% of the animals. The frequencies of the AA and BB genotypes were 12.3 and 39.5%, respectively. Allele A had a frequency of 0.36, whereas allele B had a frequency of 0.64. The chi-square value was 0.19, indicating that the observed genotype distribution was close to that expected under Hardy–Weinberg equilibrium. The mean 305-day milk yield was 5571.2 kg for AA cows, 5316.6 kg for AB cows, and 5357.2 kg for BB cows. AA cows showed numerically higher milk fat percentage and milk fat and protein yields. BB cows had a slightly higher milk protein percentage of 3.26%, compared with 3.24% in AA cows and 3.20% in AB cows. Discussion and Conclusions. The findings describe the genetic structure of the examined Simmental cattle population. Differences among genotype groups should be interpreted as descriptive numerical tendencies because statistical significance indicators for the production comparisons were unavailable. The LGB locus may therefore be considered only as a complementary, biologically interpretable component of comprehensive breeding evaluation. Further studies should use a larger and consistent sample and adjust for age, parity, lactation stage, herd management, relatedness, casein genotypes, and the polygenic background of the animals.