Polymorphism at the CSN1S1 Locus and Energy Intake Level Affect Milk Traits and Casein Profiles in Rossa Mediterranea Goats.

A total of twenty-seven Rossa Mediterranea lactating goats, consisting of nine homozygous for strong alleles (), twelve heterozygous () and six homozygous for weak alleles () at the locus, were used to evaluate the effect of genotype, diet and genotype × diet interaction on goat milk traits and casein profile. The goats were used in a 3 × 3 factorial arrangement of treatments, with three genotypes (, and ) and three different energy intake levels: high (H), medium (M) and low (L). The diets supplied a complete pelleted feed containing 65% of alfalfa hay, respectively, at 150%, 100% and 70% of the total energy requirements. Milk yield was significantly affected by the genotype and diet: Lower levels were found in goats than in and genotypes (673.7 vs. 934.5 and 879.8 d/g, respectively; 0.002) as well as in goats fed with the L diet (651.5 vs. 1041 and 852.9 g/d for H and M diet, respectively, 0.001). The genotype influenced the casein profile. Specifically, goat milk exhibited higher concentrations of total casein and α-casein compared to and genotypes (for total casein and αs1-casein, respectively: 24.9 vs. 20.4 and 19.8 g/kg, 0.001; 7.2 vs. 3.7 and 0.7 g/kg, 0.001), while the genotype showed higher values for α-casein concentrations compared to homozygous and heterozygous goats (3.1 vs. 2.4 and 2.5 g/kg, respectively, 0.001). A significant genotype x diet interaction occurred for αs2-casein levels (g/kg) ( 0.034) and αs-casein yields ( 0.027): The αs-casein level was not affected by the diet in goats, whereas it increased with energy intake in and genotypes. Conversely, the αs-casein yield gradually increased with energy intake in and groups, whereas the diet in goats did not modify it. The results demonstrated that high energy input, as well as the strong allele at the locus, enhanced milk production and casein concentrations. Furthermore, they confirmed the existence of an interaction between α-casein polymorphism and diets, influencing the milk casein composition and yield.