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

Abstract Eighteen Girgentana lactating goats, nine homozygous for strong alleles (AA) and nine homozygous for weak alleles (FF) at α s1 -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 C18) significantly increased in AA and decreased in FF goat milk. In conclusion, goats homozygous for weak and strong alleles at αs 1 -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.