Effect of feeding different postbiotics on plasma acute phase proteins (α1-AGP and CPN), and HSP70 concentrations in heat-stressed broiler chickens. a,b,c,d standard error bars sharing different letters are significantly different (p < 0.05). Data are shown as means and standard error (n = 12). α1-AGP: alpha-1-acid-glycoprotein, HSP70: heat shock protein 70, CPN: ceruloplasmin. Diets: Negative control (NC): basal diet without any supplementation, positive control (PC): basal diet + 0.02% oxytetracycline (w/w), AA: basal diet + 0.02% ascorbic acid (w/w), RI11: basal diet + 0.3% postbiotic RI11 (v/w), RS5: basal diet + 0.3% postbiotic RS5 (v/w), UL4: basal diet + 0.3% postbiotic UL4 (v/w).