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

1. Laying hen performance and yolk fat fatty acid (FA) concentrations were evaluated with respect to the inclusion in the diet of different sources and levels of marine fish oil (MFO). 2. Twelve diets were arranged factorially, with three sources (MFO1, MFO2_EPA, MFO3_DHA) and four levels of inclusion (15, 30, 45 and 60 g/kg) of MFO. 3. Type of diet had little effect on egg production traits, although laying rate and shell thickness slightly decreased at the highest level of MFO supplementation. 4. An increase in level of inclusion of MFO from 15 to 60 g/kg linearly increased concentrations of C20:5 n-3, C22:5 n-3, C22:6 n-3 and total n-3 FA in yolk fat, but greatly impaired their efficiencies of deposition (g retained/g ingested). 5. An interaction between type and dietary concentration of MFO was found, as the reduction in efficiency of retention of n-3 FA in egg fat with level of MFO was less when the proportion of n-3 in total FA decreased or when that of DHA in total n-3 FA increased. 6. MFO3_ DHA was more efficiently used for total n-3 FA yolk deposition than MFO2_EPA at a similar total n-3 FA intake. 7. Dietary inclusion of MFO reduced LC n-6 FA yolk fat content, which additionally decreased the ratio between total n-6 and total n-3 FA in egg fat. 8. Regression equations were calculated in order to predict efficiency of retention and n-3 FA concentration of yolk fat in the range of diets studied.