The current dietary recommendations for reducing the risk of cardiovascular diseases underline I) increasing MUFA intake (mainly 18:1n-9) at the expense of SFA intake (mainly 16:0) and II) increasing n-3 LC PUFA intake. Chicken egg and meat are natural sources of n-3 LC PUFA, and their consumption contributes to the intake of these semi-essential nutrients. Many efforts have been made to improve their fatty acid composition however, some aspects remain uncertain. The specific objectives of the present PhD thesis were  to study metabolism of fatty acids (accumulation and bioconversion efficiency) in broiler chickens and the impact of dietary fatty acids composition, and animal factors on the fatty acid metabolism,  to study the effect of animal factors together with diet on the fatty acid composition of muscles and organs in broiler chickens and  to study the interaction effects of dietary fatty acids on the egg yolk fatty acid composition. To fulfill these objectives, three experiments were carried out of which one trial was performed on broiler chicken and the two others on laying hens.