Polymorphism at αs1-casein locus. Effect of genotype × diet interaction on milk fatty acid composition in Girgentana goat

Eighteen Girgentana lactating goats, nine homozygous for strong alleles (AA) and nine homozygous for weak alleles (FF) at αs1-casein locus, were used to evaluate the effect of genotype × diet interaction on goat milk fatty acid composition. Animals were divided in two groups. First group consisted of 5 AA and 4 FF, the second one consisted of 4 AA and 5 FF animals. The experimental groups were used in a 2 × 2 factorial arrangement of treatments, with two genotypes (AA, FF) and two diets (D100 and D65) at different energy level (1099 and 1386 kcal NEl/kg), obtained with 100% and 65% of pelleted alfalfa hay inclusion, respectively. All the animals were housed in individual pens. The genotype × diet interaction was significant (P < 0.05) for 11 different milk fatty acids. In particular, C8:0, C10:0, C12:0, C14:0 increased when FF animals shifted from D100 to D65, while the same fatty acids did not significantly change in AA animals; moreover, percentage of palmitic acid (C16:0) was significantly lower in animals with strong genotype when fed the high energy diet. Shifting from D100 to D65, long chain fatty acids (>C18) significantly increased in AA and decreased in FF goat milk. In conclusion, goats homozygous for weak and strong alleles at αs1-casein locus seem to respond in a different way when fed diets with different energy levels; in particular, receiving a high energy diet, AA goats did not show any remarkable effect on milk fat quality, whereas FF goats showed a worsening in fat nutritional value.