Effects of dietary conjugated linoleic acids on lipid metabolism and antioxidant capacity in laying hens.

To examine the effects of dietary conjugated linoleic acids (CLA) on lipid metabolism and antioxidant capacity in laying hens, Hy-Line Brown layers (n = 384, 52 weeks old) were randomly allocated to one of four dietary treatments. Each treatment had six replicates of 16 hens each. All birds were assigned to a corn-soybean meal-based diet containing a mixture of CLA at 0%, 1%, 2% or 4% for six weeks. With increasing dietary CLA, egg weight and feed intake decreased, and yolk colour was darkened. Feed efficiency was improved at 1% and 2% dietary CLA. Serum triglyceride concentration was significantly reduced by CLA in a dose dependent manner. A linear decrease in total cholesterol and low-density lipoprotein cholesterol, and an increase in high-density lipoprotein cholesterol levels were observed after CLA supplementation. With increasing dietary CLA, the deposition of two major isomers of CLA (c9, t11; t10, c12) in yolk lipids increased linearly, the proportion of saturated fatty acids increased and monounsaturated fatty acids decreased significantly. The proportion of polyunsaturated fatty acids was highest at 1% CLA. Compared to the control, CLA supplementation significantly increased the activities of superoxide dismutase and glutathione peroxidase, inhibited hydroxyl radicals and superoxide anion production, and decreased the malonaldehyde concentrations in both serum and liver. The results demonstrated that dietary CLA meliorated serum lipid profiles and enhanced the antioxidant capacity of laying hens.