Dietary Chitosan Oligosaccharides Modulate Oxidative Status, Inflammatory and Apoptosis-Related Markers in Immune Organs of Heat-Stressed Broilers

Chitosan oligosaccharides (COS) have antioxidant and immunomodulatory activities. This study characterized immune-organ responses associated with dietary COS in broilers exposed to cyclic heat stress (HS). A total of 192 birds were assigned to four groups (six cages/group; eight birds/cage): control (CON; 24 ± 1 °C), HS (34 ± 1 °C for 10 h/day), HS + 200 mg/kg COS, and HS + 400 mg/kg COS. Each treatment was replicated in three rooms, with two cages per room. One bird per cage was sampled after the final heat-stress bout and a 12 h fast (n = 6/group). Outcomes comprised organ indices and qualitative histology; serum corticosterone; splenic and thymic SOD, CAT, GSH-Px, and MDA; and heat-shock-, cytokine-, and apoptosis-related mRNA. Data were analyzed using a linear mixed model with treatment as a fixed effect and room nested within treatment as a random effect; Tukey-adjusted comparisons followed a significant omnibus test. Treatment was assigned at room level, the CON versus HS contrast was confounded with room temperature condition, and only three rooms were available per treatment, so all inferential comparisons are exploratory. Relative to unsupplemented HS, both COS doses increased spleen and bursa indices (p < 0.05), lowered serum corticosterone (p < 0.01), increased SOD and CAT activities (p < 0.01) and GSH-Px activity (p < 0.05), and lowered MDA (p < 0.05). COS groups also showed tissue- and dose-dependent shifts in mRNA. The 200 mg/kg group generally showed the largest reductions in pro-inflammatory transcripts, whereas 400 mg/kg produced the most consistent thymic apoptosis-related transcript pattern; no single dose was optimal across all endpoints. Dietary COS was therefore associated with altered immune-organ indices, measured oxidative status, and stress-, cytokine-, and apoptosis-related transcription under HS. Because no thermoneutral + COS group was included and room-level replication was limited, these findings require validation with replicated rooms, protein measurements, and functional immune endpoints.