PROBIOTICS IN REDUCING STRESS AND INFLAMMATION

Physiological stress in poultry, which can arise from environmental factors, overcrowding, or infection, increases the production of reactive oxygen species (ROS) and activates inflammatory pathways such as NF-κB, leading to tissue damage and reduced performance [180]. NF-κB activation increases the expression of pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6, which further exacerbates inflammation and oxidative stress [181].

Probiotic supplementation, including Lactobacillus spp., Bifidobacterium spp., and Bacillus spp., has been shown to suppress NF-κB activation, thereby reducing pro-inflammatory cytokine production and preventing excessive inflammation in the gastrointestinal tract and systemic tissues [182]. Furthermore, probiotics can enhance endogenous antioxidant capacity by stimulating the expression of enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase, thereby reducing ROS levels and other markers of oxidative stress, including malondialdehyde (MDA) [183].

Nonetheless, reductions in inflammatory markers are not universally observed across all experimental conditions. In low-stress environments, probiotic supplementation sometimes results in negligible changes in H/L ratio or corticosterone levels, suggesting that benefits may be more pronounced under stress or pathogen challenge rather than under optimal management conditions [184].

The effects of probiotics on stress are also evident in physiological indicators, such as the heterophil/ lymphocyte (H/L) ratio and corticosterone levels [185]. Studies have shown that probiotic supplementation reduces the H/L ratio, a marker of chronic stress in poultry, and also reduces plasma corticosterone levels, a glucocorticoid hormone that increases in response to stress. Thus, probiotics not only reduce physiological stress and inflammation but also help maintain immune balance and support poultry performance [186].