Title : Dietary modification of yolk fatty acid profile with vegetable and fish oil
The biological significance of polyunsaturated fatty acids, in particular the n-3 PUFA, as well as the n-6/n-3 PUFA ratio, is the subject of numerous studies. For the human body, linoleic (LA, C 18:2) and linolenic (ALA, C 18: 3) acids are essential as precursors of bioactive fatty acids n-6 PUFA and n-3 PUFA. The fatty acid profile in egg yolks can be altered by modifying the laying hens' feed composition. In order to incorporate n-3 PUFA into eggs, the following two factors are significant: the transfer of utilized n-3 polyunsaturated fatty acids from feed into eggs and the endogenous metabolism of n-3 PUFA in the laying hens' bodies. The paper presents the results of research on the use of flaxseed (LO) and rapeseed oil (RO) in combination with fish oil (FO) in the feeding of laying hens and the effect on the fatty acid profile of egg yolks (∑n-3 PUFA and n-6/n-3 PUFA ratio). Nutritional treatments were as follows: C=control (5% soybean oil SO), E1=1.5% LO+3.5% FO, E2=3.5% LO+1.5% FO, E3=1.5% RO+3.5% FO, E4=3.5% RO+1.5% FO. Feed mixtures for laying hens were balanced on the basis of 17% crude protein and 11.5 MJ/kg ME, and the n-6/n-3 PUFA ratio in the mixtures was as follows: C 13.10; E1 2.69; E2 1.53; E3 4.78 and E4 6.21. The combination of flaxseed oil and fish oil in the feed affected the n-6/n-3 PUFA ratio making it narrower compared to the combination of rapeseed oil and fish oil. Control feed C contained only ALA, 4.08% being without EPA and DHA fatty acids. The analysis of the fatty acid profiles in egg yolks showed that the eggs contained 1.26% of DHA in addition to ALA, which means that, although in small amounts, DHA was synthesized and deposited in eggs by the laying hens. The following proportions of n-3 PUFAs were found in the eggs of the experimental groups: E1 6.51%, E2 8.30%, E3 5.17% and E4 3.54%. The n-6/n-3 PUFA ratio in egg yolks decreased from 11.85 (control group) to 3.08 and 2.57, respectively, for flaxseed and fish oil treatments and 4.25 and 6.38 for rapeseed and fish oil treatment. Studies have shown a more efficient deposition of n-3 PUFAs in the yolks of the E1 and E2 groups, although ALA was most abundantly present in the total n-3 PUFAs.