Effect of type and level of basal fat and level of fish oil supplementation on yolk fat composition and n-3 fatty acids deposition efficiency in laying hens

Yolk fat fatty acid (FA) concentrations and laying hen performance were evaluated with respect to the inclusion of different levels of fish oil (FO) in diets varying in basal fat. Twelve diets were arranged factorially, with three levels of FO addition (0, 15 and 30 g/kg) and four types of basal diets (no fat added or 50 g/kg of soybean oil, linseed oil or lard). Type of diet did not affect egg production traits, although yolk colour increased (by 8.7%, P<0.001) with inclusion of fat in the basal diet and decreased linearly (P=0.011) with FO supplementation. An increase of dietary inclusion of FO from 0 to 30 g/kg increased linearly (P<0.001) egg yolk content of C20:5 n-3 (EPA) and linear and quadratically (P<0.001) those of C22:5 n-3 (DPA) and C22:6 n-3 (DHA) and decreased those of C20:4 n-6 and C22:4 n-6. An interaction was found between the level of inclusion of FO and the type of basal diet, as the effects of FO addition on EPA, DPA and DHA yolk fat deposition were greater in the control and lard-added than in the linseed and soybean- added diets. Soybean and linseed oil addition to the basal diet increased (P<0.001) respectively the level of total n-6 FA (from 127 to 226 g/kg total yolk FA) and total n-3 FA (from 33 to 108 g/kg, mainly of C18:3 n-3), at the expense primarily of monounsaturated FA. Inclusion of 50 g lard/kg only increased slightly the monounsaturated FA content (by 3.3%) and had little effect on the rest of the FA profile with respect to the control diets with no fat added.