Intermittent mild cold acclimation ameliorates intestinal inflammation and immune dysfunction in acute cold-stressed broilers by regulating the TLR4/MyD88/NF-κB pathway

To investigate the potential protective effect of prior cold stimulation on broiler intestine induced by acute cold stress (ACS). A total of 384 one-day-old broilers were divided into control (CON), ACS, cold stimulation I (CS3+ACS), and cold stimulation II (CS9+ACS) groups. Broilers in CON and ACS groups were reared normally, and birds in CS3+ACS and CS9+ACS groups were reared at 3 degrees C and 9 degrees C below CON group for 5 h, respectively, on alternate days from d 15 to 35. Broilers in ACS, CS3+ACS, and CS9+ACS groups were subjected to 10 degrees C for 24 h on d 43. Eventually, small intestine tissues were collected for histopathological observation and indexes detection. The results showed that intestinal tissues in all ACS-broilers exhibited inflammatory cell infiltrates, microvilli disruption, reduced villus length in jejunum and increased crypt depth in jejunum and ileum. Whereas these phenomena were relatively light in CS3+ACS group. Compared to CON group, mRNA expression of the TLR4/MyD88/NF-kappa B pathway-related genes (TLR4, MyD88, NF-kappa Bp65, COX-2, iNOS, PTGEs, TNF-alpha), Th1/Th17-derived cytokines (IL-1 beta, IL-2, IL-8, IL-12, IFN-gamma, IL-17), and HSPs (HSP40, HSP60, HSP70, HSP90) was upregulated (P < 0.05), and that of Th2-deviated cytokines (IL-4, IL-6, IL-10, IL-13) and I kappa B alpha was downregulated (P < 0.05) in small intestine in almost all ACS-broilers. Compared to ACS group, mRNA expression of most of the TLR4/MyD88/NF-kappa B pathway-related genes, Th1/Th17-derived cytokines, and HSPs was downregulated and that of Th2-derived cytokines was upregulated in CS3+ACS group (P < 0.05). Protein expression levels of TLR4, MyD88, p-p65/p65, p-I kappa B alpha/I kappa B alpha, IKK, TNF-alpha, IL-1 beta, IL-10, and HSPs were similar to their mRNA expression. The concentration of sIgA and activities of CAT, SOD, and GSH-px were decreased and MDA and H2O2 were increased in ACS and CS9+ACS groups compared to CON group (P < 0.05). Therefore, cold stress caused oxidative stress and inflammation, leading to gut immune dysfunction; while mild cold stimulation at 3 degrees C below normal rearing temperature alleviated cold stress-induced intestinal injure and dysfunction by modulating the TLR4/MyD88/NF-kappa B pathway in broilers.