Effects of the dietary flax or grape seed oils on the egg yolk fatty acid composition and on the n-3/n-6 polyunsaturated fatty acid ratio in laying hens

The present study was carried out to examine the effects of the dietary inclusion of flax or grape seed oils on the egg yolk fatty acid composition in two consecutive trials using Brown layer hens. In each experiment, after a 2 week acclimatising period, a total of 72 hens, 28 week old, were allotted in 4 equal groups (18 birds in each group) according to the seed oil doses (0%, 1%, 2% and 4%) included into the standard diet for 8 weeks. The fatty acid composition of the egg yolk was analysed at the beginning and at the end of each experimental period by gas chromatography. When the flax seed oil (rich in alpha-linolenic acid) was included to the diet, the proportions of the lignoceric (C24:0) and the linoleic (C18:2, n-6) acids gradually decreased (P < 0.05 and P < 0.01, respectively) whereas the a-linolenic acid (Cl 8:3, n-3) percentage and the n-3 / n-6 ratio significantly increased according to the included dose (P < 0.01) in the egg yolk. On the contrary, the yolk lignoceric acid content increased (P < 0.05) and the a-linolenic acid proportion as well as the n-3 / n-6 ratio significantly decreased in a dose-dependant manner (P < 0.05) when the grape seed oil (rich in linoleate) was used. These results show that the dietary inclusion of I% to 4% seed oils significantly affects the yolk acid composition and mainly the a-linoleate proportions and the n-3 / n-6 ratio and that the flax seed oil contrary to the grape seed oil induced a marked accumulation of the n-3 acid in yolk probably by promoting its direct deposition.