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Dietary conjugated linoleic acid (CLA) causes adverse effects on quality of eggs by modifying the fatty acid composition of the yolk. Supplementing oils prevent CLA-induced changes, but cause a decrease in the level of egg CLA. The objective of the study was to investigate the incorporation of CLA into the egg and its effect on the fatty acid metabolism when laying hens were fed diets containing different levels of canola oil. Hens (15 per group) were assigned to six groups and were fed for 50 days diets containing 0.5% canola oil (Group A), 0.5% CLA (Group B), 0.5% CLA plus 1.25% canola oil (Group C), 0.5% CLA plus 2.5% canola oil (Group D), 0.5% CLA plus 5% canola oil (Group E) or 0.5% CLA plus 10% canola oil. Eggs were collected daily. Three eggs per group were used for fatty acid analysis. Eggs laid on days 1 to11 were stored at 4 °C or room temperature for 30 days, and were separated into yolk and albumen for pH analyses. Yolk from Group B had increased concentrations of C16:0 and C18:0 and decreased concentrations of C18:1(n-9) compared to Group A. Adding 5% or 10% canola oil (Groups E or F) to the diet prevented an increase in C16:0 and C18:0 and a decrease in C18:1(n-9) concentrations. Relative amounts of CLA in eggs from Groups A, B, C, D, E and F were 0, 2.38, 2.33, 1.68, 1.36, and 1.17%, respectively. The concentrations of C18:3(n-3) in Groups A, B, C, D, E and F were 0.23, 0.25, 0.61, 0.70, 1.23 and 1.58%, respectively. The ratios of UFA/SFA in the eggs from Groups B, C and D decreased. When the eggs were stored at 4 °C, the yolk from Groups B, C and D had higher pH values than the other treatments, while the albumen pH of eggs from Groups B, C and D were lower. However, when eggs were stored at room temperature, no abnormal pH changes were observed in the yolk or albumen. This study suggested that adding a certain level of canola oil rich in n-3 fatty acids restored the level of egg yolk SFA to UFA, prevented CLA-induced abnormal changes in egg quality and thus led to a higher level of C18:3(n-3) and CLA in the egg. Keywords : Conjugated linoleic acid; unsaturated fatty acids; egg yolk and albumen pH; chickens South African Journal of Animal Sciences Vol. 35 (3) 2005: pp.172-179

The effects of conjugated linoleic acid (CLA) and canola oil on the fatty acid composition and quality of eggs from laying hens