As an important respiratory organ, the lung is susceptible to damage during heat stress due to the accelerated breathing frequency caused by an increase in environmental temperature. This can affect the growth performance of animals and endanger their health. This study aimed to explore the mechanism of lung tissue damage caused by heat stress. Broilers were randomly divided into a control group (Control) and a heat stress group (HS). The HS group was exposed to 35°C heat stress for 12 h per d from 21-days old, and samples were taken from selected broilers at 28, 35, and 42-days old. The results showed a significant increase in lactate dehydrogenase (LDH) activity in the serum and myeloperoxidase (MPO) activity in the lungs of broiler chickens across all 3 age groups after heat stress (P < 0.01), while the total antioxidant capacity (T-AOC) was significantly enhanced at 35-days old (P < 0.01). Heat stress also led to significant increases in various proinflammatory factors in serum and expression levels of HSP60 and HSP70 in lung tissue. Histopathological results showed congestion and bleeding in lung blood vessels, shedding of pulmonary epithelial cells, and a large amount of inflammatory infiltration in the lungs after heat stress.

The spleen is the largest peripheral immune organ of the organism, accounting for 25% of the total lymphoid tissue of the body. During HS, the spleen is damaged due to the elevated environment, which seriously affects life performance and broilers’ health. This study aimed to investigate the mechanism of chronic HS damage to broiler spleen tissues. The broilers were typically raised until they reached 21 days of age, after which they were arbitrarily allocated into two groups: an HS group and a cntrol group. The HS group was subjected to a temperature of 35 °C for 10 h each day, starting at 21 days of age. At 35 and 42 days of age, spleen and serum samples were obtained from the broilers. The results showed that after HS, a significant decrease in productive performance was observed at 42 days of age (p < 0.01), and the spleen index, and bursa index were significantly decreased (p < 0.01). T-AOC of the organism was significantly decreased (p < 0.05), GSH-PX, SOD, and CAT antioxidant factors were significantly decreased (p < 0.01), and MDA was significantly elevated (p < 0.01). HS also led to a significant increase in cytokines IL-6, TNF-α, and INF-γ and a significant decrease in IL-4 in the spleen. The histopathologic results showed that the spleen’s red-white medulla was poorly demarcated. The cells were sparsely arranged after HS. After HS, the expression of TLRs, MYD88, and NF-κB genes increased significantly. The expression of HSP70 increased significantly, suggesting that HS may induces an inflammatory response in broiler spleens through this signaling pathway, which may cause pathological damage to broiler spleens, leading to a decrease in immune function and progressively aggravating HS-induced damage with the prolongation of HS.

Capsular type A and D strains of Pasteurella multocida are the main epidemic serogroups in pigs in China. In this study, we preliminarily evaluated the immune protective efficacy of the two traditional vaccines, an inactivated C44-1 aluminum-hydroxide-gel-adjuvanted (Alh–C44-1) vaccine and a live EO630 vaccine, against currently circulating strains of P. multocida in a mouse model. Mice immunized twice with conventional vaccines generated higher antibody titers, and significantly higher levels of IgG were observed in the mice inoculated with the inactivated Alh–C44-1 vaccine on day 35 (p < 0.05) than those with the live EO630 vaccine. The mice immune protection test showed that the vaccination groups had a 57% or 71% protection effect against the serogroup B strain, but had no protective effect against epidemic strains. In conclusion, our study found that the widely used traditional P. multocida vaccines in China provide good protection against homologous strains, but could not provide cross-protection against heterologous strains in a mouse model.

Background: High-temperature environment can cause acute kidney injury affecting renal filtration function. To study the mechanism of renal injury caused by heat stress through activates TLR4/NF-κB/NLRP3 signaling pathway by disrupting the filtration barrier in broiler chickens. The temperature of broilers in the TN group was maintained at 23 ± 1 °C, and the HS group temperature was maintained at 35 ± 1℃ from the age of 21 days, and the high temperature was 10 h per day, and one broiler from each replicate group at the age of 35 and 42 days was selected for blood sampling, respectively. Results: The ELISA results demonstrated that in comparison to the TN group, serum CORT content of broilers in the HS group was all remarkably elevated (P < 0.01); the levels of IL-6 and TNF-α in the serum were remarkably elevated (P < 0.05 or P < 0.01); serum CAT and SOD activities were all remarkably reduced (P < 0.05 or P < 0.01), and serum LDH activity and MDA content were all remarkably decreased (P < 0.05); serum BUN and CRE levels were remarkably elevated (P < 0.01). Pathological sections and transmission electron microscopy demonstrated that the structure of the renal filtration barrier in the HS group damaged gradually with the prolongation of heat stress in comparison to the TN group, but the damage was reduced at 42 days of age; the levels of TLR4, MyD88, NF-κB, NF-κB-p65, NLRP3, caspase-1 and IL-1β mRNAs were all up-regulated (P < 0.05 or P < 0.01) in renal tissues of the HS group, indicating that heat stress caused damage to the morphological structure and function of the renal filtration barrier and that TLR4/NF-κB/NLRP3 pathway was also affected by heat stress, leading to increased activity (P < 0.05 or P < 0.01). Conclusions: It demonstrated that heat stress caused detrimental effects on both the morphological structure and function of the renal filtration barrier, and the initiation of the TLR4/NF-κB/NLRP3 signaling pathway exacerbated the inflammatory damage, leading to increased thermal damage to renal tissues and glomerular filtration barriers; however, with the prolongation of heat stress, broilers gradually developed heat tolerance, and the damage to the renal tissues and filtration barriers triggered by heat stress was mitigated.

The liver accounts for almost 95% of lipid metabolism in broilers and serves as a crucial metabolic organ. Stress, which occurs when broilers are exposed to a heated environment, inhibits liver metabolism, significantly impacting their growth. This experiment investigated the combination of GBE with TP to improve hepatic lipid metabolism in heat-stressed broiler chickens by inhibiting the AMPK/SREBP-1C/ACC pathway. Three hundred broilers were reared usually until 21 days and randomly divided into six groups, namely CON group, HS group, TP group (300 mg/kg), GBE100 group (GBE100 mg/kg + TP300 mg/kg), GBE300 group (GBE 300 mg/kg + TP 300 mg/kg), GBE600 (600 mg/kg + TP 300 mg/kg) groups, where the CON group was kept at 23 °C, and the HS group and the TP, GBE100, GBE300, and GBE600 groups of each medication group were kept at 35 ± 2 °C for 10 h per day. Liver and serum samples were extracted at 28 and 42 days of age, respectively. The results showed that, at 42 days of age, the GBE600 group exhibited significantly superior performance to the HS group in ADG, ADFI, and F/G (p < 0.01). Serum TG, TC, and LDL-C levels were significantly lower (p < 0.01), while HDL-C levels were significantly higher (p < 0.05). Additionally, the mRNA expression levels of LKB1, AMPK, SREBP-1C, and ACC were markedly reduced (p < 0.01). In contrast, the mRNA expression of HSL and CPT1A was significantly elevated (p < 0.01), indicating that the GBE600 was more effective in mitigating heat stress in broiler chickens at 42 days of age. It showed that the GBE600 was more effective in ameliorating heat stress in broilers at 42 days of age, thus providing an ethical basis for ameliorating the flocculation of hepatic lipid metabolism in heat-stressed broilers.

Heat stress is a major environmental stressor in poultry production that reduces growth performance and induces oxidative stress, inflammatory responses, and lung tissue injury. This study investigated the protective effects of dietary supplementation with Ginkgo biloba extract and tea polyphenols against heat stress-induced lung injury in broilers. A total of 320 one-day-old broilers were reared under standard management conditions until 21 days of age. Subsequently, 300 birds with similar body weight were selected and randomly allocated into six groups: a thermoneutral control group, a heat stress group, a heat stress group supplemented with 300 mg/kg tea polyphenols, and three heat stress groups receiving 300 mg/kg tea polyphenols combined with 100, 300, or 600 mg/kg Ginkgo biloba extract. The analysis of the results showed that heat stress significantly reduced the average daily gain and feed intake while increasing the feed conversion ratio. It also markedly increased serum lactate dehydrogenase activity and malondialdehyde levels, while decreasing antioxidant-related indicators, indicating the occurrence of oxidative stress and inflammatory responses. Histological examination revealed lung injury characterized by alveolar wall thickening, epithelial cell shedding, and disruption of the endothelial barrier, accompanied by upregulated expression of heat shock proteins and inflammation-related signaling genes. Supplementation with tea polyphenols alone partially alleviated these changes. Notably, the combined supplementation of Ginkgo biloba extract and tea polyphenols exerted more pronounced protective effects, significantly enhancing antioxidant capacity, attenuating inflammatory responses, and maintaining pulmonary barrier integrity. Among the tested levels, the groups receiving 300 mg/kg Ginkgo biloba extract in combination with tea polyphenols showed the most evident improvements. These findings suggest that the combined use of these plant-derived extracts effectively mitigates heat stress-induced lung injury in broilers.