Abstract INTRODUCTION: This experiment was conducted to study the effects of different levels of flaxseed (0, 5, 10 and 15% of diet) and copper (in the form of cupric sulfate pentahydrate, 0 and 250 ppm of diet) on fatty acids and cholesterol in egg yolk of laying hens. methods: A total of 128 White Leghorn layers aged 50 weeks were used in a factorial design and randomly assigned to 8 treatment groups. The experiment lasted 120 days. The birds were fed ad libitum on the experimental diets. Cholesterol concentration and fatty acids in plasma and egg yolk were measured monthly and bimonthly, respectively. Egg yolk cholesterol was extracted using modified Folch procedure and measured using Zak's method. results: The results showed that experimental diets had no effect on plasma cholesterol. The different levels of flax had no significant effect on egg yolk cholesterol but the presence of copper with flax at levels of 5 and 10 percent decreased cholesterol in egg yolk (mg per gram yolk) significantly (P<0.05). The egg cholesterol (mg per egg) in the group treated with 15% flax without copper also decreased significantly (P<0.05). The unsaturated fatty acids of egg yolk increased significantly in all experimental diets (P<0.05). The highest ratio of omega-3 to omega-6 fatty acids was observed in groups treated with 10% and 15% flax diets. DISCUSSION: This experiment showed that feeding flaxseed to laying hens can increase omega-3 fatty acids of egg yolk. Keywords • Laying hen • Egg yolk • Flax • Copper • Plasma • Cholesterol • Fatty acid

A. Azarbayejani

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