Chronic heat stress inhibited the growth performance of broilers.
Growth performance indexes of broilers are mainly reflected in body weight growth and feed conversion capacity. The daily body weight and feed intake of broilers were monitored in this study, and the results were shown in table 2. Compared with the control 1 group, the body weight gain of broilers in the HS1 group were significantly decreased (P < 0.01), and the feed intake and gain feed ration also inhibited by heat stress but it is no significantly. With the enhanced of adaptability, these adverse reactions gradually ameliorate, and there is no significant difference between control 2 and HS 2 group, however, the performance of HS2 group still affected by heat stress.
Effects of heat stress on liver weight, index and pathological changes of broilers.
The liver of broilers after necropsy was observed (Figure. 1A). It showed that the texture of the liver surface in the control 1 group (a) and the control 2 group (c) broilers were uniform, without obvious bleeding and necrosis points. HS1 group (b) and HS2 group (d) broilers showed obvious blutpunkte on the liver surface. The results showed that heat stress had a promotion on liver tissue damage. We also measured the body weight, liver weight and liver index, and the results showed that the above 3 indicators were significantly reduced after 2 weeks of heat stress, compared with control 2 group.
Chronic heat stress enhanced proteins expressions of TNF-α and IL-6 in liver of broilers.
As shown in Figure.2, compared with the control 1 and 2 group, heat stress significantly increased the protein expression of IL-6 in liver after 1 and 2 weeks of heat stress (P < 0.01, P < 0.01, respectively). The TNF-α protein levels in broilers with heat stress for 1 and 2 weeks were higher than that of in control 1 and 2 group broilers (P < 0.01, P < 0.01, respectively).
Chronic heat stress activated the NLRP3 pathways in liver of broilers.
As shown in Figure 3. compared with the control 1 and 2 group, the NLRP3 and caspase1 protein levels in HS1 and HS2 group both significantly increased (P < 0.01, P < 0.01, P < 0.01, P < 0.01, respectively). The level of cleaved-IL-1β/pro-IL-1β in liver of HS1 and HS2 group broilers were obviously higher than that of in control 1 and 2 group (P < 0.01, P < 0.01). The trend of cleaved-IL-1β/pro-IL-1β was consistent with proteins expressions of NLRP3 and caspase1.
Chronic heat stress strengthened NF-κB pathways in liver of broilers.
We simultaneously detected the expression of NF-κB, IκB-α and their phosphorylated protein levels. The results were shown in Figure 4. Compared with control 1 and 2 group, 1 and 2 weeks of heat stress significantly increased the ratio of phosphorylation of NF-κB to NF-κB (P < 0.01, P < 0.01, respectively), and also enhanced the ratio of phosphorylation to non-phosphorylation of IκB-α (P < 0.01, P < 0.01, respectively).
Chronic heat stress promoted the proteins expressions of TLR4 and HSP70 in liver of broilers.
As shown in the Figure 5, the proteins expression of TLR4 and HSP70 in the liver of broilers were measured. Heat stress for 1 and 2 weeks significantly up-regulated the protein expression of TLR4, compared to control 1 and 2 group (P < 0.01, P < 0.01, respectively). HSP70 protein has a protective effect on cells, and its nonspecific expression can be increased when the body is subjected to stress. Our results found that, compared with the control 1 and 2 group, the protein expression of HSP70 in HS1 and HS2 group were significantly increased (P < 0.01, P < 0.01, respectively).
Chronic heat stress up-regulated the genes expressions of TLR4, HSP70 and NF-κB in liver of broilers.
As shown in the Figure 6, heat stress for 1 and 2 weeks enhanced TLR4 gene expression (P < 0.01, P < 0.01, respectively), especially at 2 weeks of heat stress. An increase in HSP70 mRNA was observed in the liver after heat stress for 1 and 2 weeks, compared to control 1 and 2 group (P < 0.01, P < 0.01, respectively). Consistently, NF-κB gene expression was also significantly upregulated during heat stress.