The incorporation of n-3 FA into egg yolk fat (designer/enriched or omega-3 eggs) can be easily accomplished by feeding laying hens diets containing flaxseed (LO) and FO, sources of PUFAs. Studies have demonstrated that the FA composition of yolk can be manipulated by the type of dietary fat sources, whereas, the egg yolk total fat contents cannot be altered (Baucells et al., 2000; Ebeid et al., 2008; Garcia-Rebollar et al., 2008). FO is rich in long-chain n-3PUFA (EPA and DHA) and LO contains only a-linolenic acid (ALA; 18:3n-3), in greater amounts, which is the precursor of EPA and DHA. The ALA is converted into EPA and DHA by the hen’s liver and the synthesized fatty acids are subsequently excreted with the egg yolk (Simopoulos, 2000).

Contradictory results have been reported concerning the possible effects of such n-3-enriched diets on layer performance and egg quality characteristics. Several reports have revealed that supplementing n-3PUFA into the diet had no significant effects on egg production, egg weight and egg quality characteristics (Liu et al., 2003; Garcia-Rebollar et al., 2008; Da Silva et al., 2009). Similarly, Guo et al. (2004) have reported that diet containing 5% fish oil did not significantly influence egg production of hens. By contrast, Cortinas et al. (2003) summarized that egg production was significantly higher when laying hens were fed diets containing 4% FO or flaxseed oil. Cachaldora et al. (2008) indicated that yolk color increased in the diets supplemented with n-3 oils with respect to the control diets. Samman et al. (2009) stated that eggshell weight, expressed as a percentage of total egg weight, was highest in n-3 eggs. Ebeid (2011) also reported non-significant effects of dietary FO or LO supplementation on hen-day egg production, feed intake, egg weight, egg shape index, albumen height, Haugh units and yolk height. However, dietary FO and/or LO supplementation had a significantly positive effect on eggshell percentage, eggshell thickness and yolk color.

Flaxseed (Linseed), either oil or ground seed, is considered to be an excellent source of LA that favours its subsequent transfer into eggs. Ferrier et al., (1995) reported that feeding leghorn pullets with diets having 0, 100, or 200 g/kg ground flax seed progressively increased the omega-3 fatty acid contents, α-linolenic acid; 28, 261, and 527 mg/egg and DHA; 51, 81, and 87 mg/ egg, respectively) but did not alter the egg cholesterol concentration. Although use of flaxseed in layer feed was reported up to 30%, but its efficacy usually decreased when added in poultry diets more than 10 % (Gonzalez-Esquerra and Leeson, 2001). Unpleasant taste of eggs has been also found with greater levels of flaxseed (Jiang et al., 1992; Caston et al., 1994). Canola oil and seeds could also enhance the linolenic acid content of eggs. Eggs with more than 200 mg of omega-3 fatty acids can be produced by supplementing layer diets with 16 % canola seed (Cherian and Sim, 1991). Collins et al. (1997) used corn with pearl millet in laying hens rations and reported that pearl millet feeding significantly decreased yolk pigmentation and produced eggs significantly enriched in omega-3 fatty acids. Omega-6 fatty acids to omega-3 fatty acids ratios in eggs were 13.1, 10.1, and 8.3 for hens fed corn, corn plus pearl millet, and pearl millet, respectively. Diets containing barley and oats, wheat and maize with regular oats, supplemented with adequate amounts of blended animal fat are considered favorable to increase the level of omega-3 fatty acids and decreasing the omega-6 to omega-3 ratio in egg yolks (Kaminska, et al.,

2001).  Hayat (2009) compared canola, sunflower and full fat flax seed at different levels and concluded that the content of n-6 FA and total PUFA (n-6+n-3) was highest (P<0.05) in eggs from hens fed 15% sunflower diet. However, Flaxseed (100 g/kg diet) was found to be optimum with respect to egg omega-3 fatty acid content and feed efficiency.

Fish oils from different kinds of fish had extensively used to enrich eggs with long chain omega-3 PUFA (Oh et al., 1991; Gonzalez-Esquerra and Leeson, 2000; Shimizu et al., 2001; Güçlü et al., 2008). Fish meal (Nash et al., 1995, 1996), marine algae (Herber and Van Elswyk, 1996), or a combination of several marine sources (Baucells et al., 2000) in hen diets may also contribute to the omega-3 content in eggs. However, supplementation with fishmeal or fish oil can exert a damaging effect on the sensory attributes of the egg (Nash et al., 1996). Levels above three percent fish oil and ten percent fish meal may lead to unfavorable ‘fishy’ taste in eggs.

In general, the concentrations of n-3, n-6 and total PUFA of egg yolk is dependent upon the dietary source of these acids (Baucells et al., 2000; Grobas et al., 2001; Basmacıoglu et al., 2003; Eseceli & Kahraman, 2004; Zafar, 2009).