Effect of Kappa Casein and Beta Lactoglobulin Genetic Variants on Milk Composition Traits in Tunisian Oasis Autochthonous Goats

Abstract

The undertaken study was planned to investigate the influence of genetic variants of β-lactoglobulin and κ-casein loci on milk composition traits in two autochthonous Arbi and Serti goats raised in Tunisia's continental oasis region. For this purpose, blood and milk from 177 multiparous and unrelated animals were collected and used. Milk samples were analyzed for physical parameters, chemical composition, and mineral concentrations using standard methods. PCR amplification was performed using DNA samples and specific primers targeting exon 7 and 4 of β-lactoglobulin and κ-casein, respectively. To detect genetic variants, amplified products were digested with the restriction enzymes SmaI for β-lactoglobulin and HaeIII for κ-casein. The κ-casein protein had two alleles A and B, as well as two genotypes AA and AB, whereas the β-lactoglobulin showed two alleles C and T, and three genotypes CC, TT, and CT. Allele A of κ-casein occurred at a higher frequency than allele B in Arbi and Serti subpopulations and overall population. The β-lactoglobulin C allele was more common than T allele in Arbi and Serti subpopulations and throughout population. Homozygotes' frequencies were found to be higher than those of heterozygotes in all animals. Genetic polymorphism of β-lactoglobulin has been linked to milk acidity, dry matter, protein, casein, fat, lactose, Ca, P, and k content, with homozygous TT and CC genotypes clearly outperforming CT genotype. The κ-casein locus had a marked influence on the dry matter, protein, casein, and fat components, favoring homozygous AA goats in all traits except fat, which distinguished heterozygous AB goats.