Effects of diet on casein and fatty acidprofiles of milk from goats differing ingenotype for αS1-casein synthesis

This study investigated the interactions betweennutrition and the genotype at αS1-CN loci (CSN1S1) ingoats, evaluating the impact of fresh forage-based dietsand an energy supplement on the casein and fatty acid (FA)profiles of milk from Girgentana goats. Twelve goats wereselected for having the same genotype at the αS2-CN, β-CN, and κ-CN loci and differing in the CSN1S1 genotype:homozygous for strong alleles (AA) or heterozygous forstrong and weak alleles (AF). Goats of each genotype weredivided into three groups and, according to a 3 × 3 Latinsquare design, fed ad libitum three diets: sulla fresh forage(SFF), SFF plus 800 g/day of barley (SFB), and mixedhay plus 800 g/day of barley (MHB). The SFB diet led tohigher-energy intake and milk yield. The energy-supplementeddiets (SFB, MHB) reduced milk fat and urea andincreased coagulation time. The fresh forage diets (SFF,SFB) increased dry matter (DM) and crude protein (CP)intake and milk β-CN. Diet had a more pronounced effectthan CSN1S1 genotype on milk FA profile, which washealthier from goats fed the SFF diet, due to the higher contentof rumenic acid, polyunsaturated, and omega-3 FAs.The AA milk had longer coagulation time and higher curdfirmness, higher short- and medium-chain FAs (SMFA),and lower oleic acid than AF milk. Significant diet by genotypeinteractions indicated the higher milk yield of AAgoats than AF goats with the higher-energy SFB diet andthe lower synthesis of SMFA in AF than in AA goats withthe SFF diet.