Effect of stocking density and alpha-lipoic acid on the growth performance, physiological and oxidative stress and immune response of broilers

Objective: The study was conducted to evaluate the effect of stocking density and alphalipoic acid (ALA) on the growth performance, feed utilization, carcass traits, antioxidative ability and immune response of broilers. Methods: A total of 1,530 22-day-old male broilers (Arbor Acres) with comparable body weights ($731.92{\pm}5.26$) were placed into 18 cages ($2.46{\times}2.02m$) in groups of 75 birds ($15birds/m^2$, $37.5kg/m^2$; low stocking density [LD]), 90 birds ($18birds/m^2$, $45.0kg/m^2$; high stocking density [HD]) and 90 birds with 300 mg/kg ALA added to the basal diet ($18birds/m^2$, $45.0kg/m^2$; HD+ALA, high stocking density+${\alpha}$-lipoic acid); each treatment was represented by 6 replicates. The experimental period was 3 weeks. Results: The results showed that the high stocking density regimen resulted in a decreased growth, feed conversion ratio, carcass weight, thigh yield and bursa weight relative to body weight (p<0.05) on d 42. The abdominal fat yield in the HD+ALA group was lower (p = 0.031) than that of the LD group at 42 d. The superoxide dismutase and glutathione peroxidase activities in serum were increased, and malondialdehyde content decreased after adding ALA product (p<0.05) on d 42. Additionally, the serum concentrations of immunoglobulin A (IgA) and IgG were decreased (p<0.05) and the level of diamine oxidase was higher (p<0.01) in the HD group on d 42. Conclusion: The high stocking density significantly decreased broiler growth performance, feed utilization and carcass traits, increased physiological and oxidative stress and induced intestinal mucosal injury. The supplementation of ALA product in broiler diet at 300 mg/kg may reduce the adverse effects of high stocking density-mediated stress by maintaining the antioxidant system and humoral immune system.