Effects of conjugated linoleic acid on growth performance and physiological responses of broiler chickens reared under high stocking density

This study investigated the biological effects of dietary conjugated linoleic acid (CLA) in broiler chickens raised at different stocking densities. A total of 540 feather-sexed female broiler chicks (Ross 308) were randomly assigned to one of 28 floor pens in a 2 × 2 factorial arrangement with two stocking densities (800 cm² and 1,300 cm² per chick) and two levels of dietary CLA (0 and 10 g/kg). Each treatment consisted of seven replicates and the experiment lasted for five weeks. Dietary CLA lowered the feed intake (P = 0.038) but improved the feed conversion ratio (P = 0.035) in broiler chickens at day 21. Broilers raised under high vs. low stocking densities ate and gained less during the finisher and whole phases. In contrast, high vs. low stocking densities improved (P < 0.001) feed conversion ratio at the starter phase. None of the main factors (stocking density and CLA) affected the rectal temperature and secretory immunoglobulin A content of the ileal mucosa (P > 0.05). Tibial characteristics were negatively affected by stocking density at day 35. Dietary CLA increased the concentration of glutamic oxaloacetic transaminase (P = 0.009) and total cholesterol (P = 0.079) in serum samples compared to the control group fed a CLA-free diet. Antioxidant parameters, including superoxide dismutase and malondialdehyde, were not altered (P > 0.05) by the stocking density or dietary CLA. Dietary CLA tended to increase corticosterone levels in the serum samples of broiler chickens raised under a high stocking density, exhibiting a partial interaction between the main factors (P = 0.086). Dietary CLA, but not stocking density, altered the fatty acid composition of thigh meat (P < 0.05). In summary, dietary CLA improved the fatty acid composition of broiler meat while maintaining normal growth performance, and its efficacy was independent of stocking density.