Cryptosporidium spp. cause diarrheal disease worldwide. Innate immune responses mediating resistance to this parasite are not completely understood. To determine whether MyD88-dependent pathways play a role in resistance to Cryptosporidium parvum, we compared the course of infection in MyD88 ؊/؊ mice to that in their wild-type (WT) littermate controls. Three-to 4-week-old mice were infected with C. parvum, and infection was monitored by quantifying fecal oocyst shedding. Twelve days postinfection, the histology of the intestines was examined to quantify intestinal parasite burden and to determine if there were any pathological changes. Fecal oocyst shedding and intestinal parasite burden were significantly greater in MyD88 ؊/؊ mice than in littermate controls. Nonetheless, both WT and MyD88 ؊/؊ mice cleared the infection within 3 weeks. These results indicate that MyD88-dependent pathways are involved in mediating initial resistance to C. parvum. Since gamma interferon (IFN-␥) is known to mediate resistance to C. parvum, we also studied infection in MyD88؊/؊ mice and WT controls in which this cytokine was temporarily neutralized. Fecal oocyst shedding, as well as intestinal parasite burden, intestinal inflammation, and mortality, was significantly greater in MyD88 ؊/؊ mice in which IFN-␥ was neutralized than in IFN-␥-neutralized WT mice or in MyD88 ؊/؊ mice in which this cytokine was active. These results suggest that MyD88 and IFN-␥ had an additive effect in conferring protection from C. parvum infection. While this study confirms the importance of IFN-␥ in conferring resistance to infection with C. parvum, it suggests that MyD88-mediated pathways also play a role in innate immunity to this parasite.

The heterophil/lymphocyte (H/L) ratio has been extensively studied to select poultry that are resistant to environmental stressors. Chickens with a low H/L ratio are superior to the chickens with a high H/L ratio in survival, immune response, and resistance to Salmonella infection. However, this disease resistance ability is likely to be associated with enhanced intestinal immunity. Therefore, to expand our understanding of these underlying resistance mechanisms, it is crucial to investigate the correlation between the H/L ratio as a blood immune indicator in live chickens and the intestinal barrier function and immunity. Jinxing yellow chickens H/L line one-day-old were divided into non-infected (NI) and Salmonella enteritidis infected (SI) at 7-days old. After dividing the birds into NI and SI, blood samples were taken for H/L ratios determination, and subsequently, birds from the SI group were infected with Salmonella enteritidis (SE). We assessed the effects of SE infection on the (i) goblet cells number from the ileum and caecum gut-segments, (ii) ileal mucosa morphology, and (iii) immune gene mRNA expressions from the ileum and caecum of NI and SI chickens at 7 and 21 days-post-infection (dpi). We found that the H/L ratio was negatively correlated with most intestinal immune indices, particularly with the goblet cells number and with IL-1β, IL-8, and IFN-γ ileal expressions. In conclusion, these results suggest that the H/L ratio is associated with the intestinal barrier and immune response for SE clearance and that the chickens with a low H/L ratio displayed enhanced intestinal immunity. This study expands the current knowledge that is related to using the H/L ratio to select and breed resistant broiler chickens.

The gastrointestinal microbiota plays a vital role in ensuring the maintenance of host health through interactions with the immune system. The Heterophil/Lymphocyte (H/L) ratio reflects poultry’s robustness and immune system status. Chickens with low H/L ratio are superior to the chickens with high H/L ratio in survival, immune response, and resistance to Salmonella infection, but the underlying mechanisms remain unclear. This study aimed to identify microorganisms associated with resistance to Salmonella Enteritidis infection in chickens based on the H/L ratio. The 16S rRNA and metagenomic analysis were conducted to examine microbiome and functional capacity between the 2 groups, and Short Chain Fatty Acids (SCFAs) and histopathology were conducted to explore the potential difference between susceptible and resistant groups at 7 and 21 days post-infection (dpi). The microbiome exploration revealed that low H/L ratio chickens, compared to high H/L ratio chickens, displayed a significantly higher abundance of Proteobacteria (Escherichia coli) and Bacteroidetes (Bacteroides plebeius) at 7 and 21 dpi, respectively. Anaerostipes (r = 0.63) and Lachnoclostridium (r = 0.63) were identified as bacterial genus significantly correlated with H/L (P < 0.001). Interestingly, Bacteroides was significantly and positively correlated with bodyweight post-infection (r = 0.72), propionate (r = 0.78) and valerate (r = 0.82) contents, while Salmonella was significantly and negatively correlated with bodyweight post-infection (r = − 0.67), propionate (r = − 0.61) and valerate (r = − 0.65) contents (P < 0.001). Furthermore, the comparative analysis of the functional capacity of cecal microbiota of the chickens with high and low H/L ratio revealed that the chickens with low H/L ratio possess more enriched immune pathways, lower antibiotic resistance genes and virulence factors compared to the chickens with high H/L ratio. These results suggest that the chickens with low H/L ratio are more resistant to Salmonella Enteritidis, and it is possible that the commensal Proteobacteria and Bacteroidetes are involved in this resistance against Salmonella infection. These findings provide valuable resources for selecting and breeding disease-resistant chickens.

Heat stress is one of the most prevalent issues in poultry production that reduces performance, robustness, and economic gains. Previous studies have demonstrated that native chickens are more tolerant of heat than commercial breeds. However, the underlying mechanisms of the heat tolerance observed in native chicken breeds remain unelucidated. Therefore, we performed a phenotypical, physiological, liver transcriptome comparative analysis and WGCNA in response to heat stress in one native (Beijing You, BY) and one commercial (Guang Ming, GM) chicken breed. The objective of this study was to evaluate the heat tolerance and identify the potential driver and hub genes related to heat stress in these two genetically distinct chicken breeds. In brief, 80 BY and 60 GM, 21 days old chickens were submitted to a heat stress experiment for 5 days (33 °C, 8 h/day). Each breed was divided into experimental groups of control (Ctl) and heat stress (HS). The results showed that BY chickens were less affected by heat stress and displayed reduced DEGs than GM chickens, 365 DEGs and 382 DEGs, respectively. The transcriptome analysis showed that BY chickens exhibited enriched pathways related to metabolism activity, meanwhile GM chickens’ pathways were related to inflammatory reactions. CPT1A and ANGPTL4 for BY chickens, and HSP90B1 and HSPA5 for GM chickens were identified as potential candidate genes associated with HS. The WGCNA revealed TLR7, AR, BAG3 genes as hub genes, which could play an important role in HS. The results generated in this study provide valuable resources for studying liver transcriptome in response to heat stress in native and commercial chicken lines.