Mitigating high-density housing stress in broilers: a comparative evaluation of vitamin E vs. Zinc on immunity, molecular markers, carcass yield, and profitability.

The present study investigated the effects of stocking density (StD) on growth traits, carcass cuts, immune responses, and economic efficiency in broiler chickens, and evaluated whether dietary supplementation with vitamin E (Vit E) or zinc (Zn) could mitigate the adverse effects of high StD. A total of 636 one-day-old male Cobb chicks were allocated to seven experimental groups representing low (LStD; 23 kg/m²), moderate (MStD; 34 kg/m²), and high (HStD; 39 kg/m²) stocking densities. Selected MStD and HStD groups received either zinc or vitamin E supplementation at 100 mg/kg dietary dry matter (DM). Medium and high stocking densities significantly reduced feed intake, cumulative weight gain, carcass yield, and economic returns, while increasing stress indicators and hepatic HSP70 gene expression (P < 0.05). Birds reared under these stocking densities also showed impaired humoral immunity, reflected by lower plasma IgM, IgG, and IgA concentrations and reduced expression of interferon-γ, IL-1β, IL-4, and SOD mRNAs. Supplementation with either Zn or Vit E effectively alleviated these adverse effects by improving growth performance, immune function, antioxidant status, and economic profitability. In conclusion, the findings indicate that dietary Zn supplementation at 100 mg/kg DM allows the stocking density to be increased from 23 to 34 kg/m² while maintaining productivity. In addition, supplementation with either Zn or Vit E provides a practical nutritional strategy for maintaining health, immunity, and production efficiency under intensive rearing conditions.