Enhancing phagocytic capacity in layer chickens: a one health approach to sustainable production through improved disease resistance and reduced antibiotic dependence.

BACKGROUND

Reducing antibiotic dependence in poultry production is critical to mitigating antimicrobial resistance (AMR). Selective breeding for stronger innate immunity may provide a sustainable alternative under a One Health framework. This study investigates whether enhancing monocyte/macrophage phagocytic capacity in layer chickens could improve disease resistance without compromising production performance under antibiotic-free conditions.

METHODS

Phagocytic capacity was assessed using multiple assays. Phagocytosis product (PP) was measured using the MTT-HCT-8 method, pHrodo-labeled E. coli, and FITC-labeled S. pullorum, whereas the phagocytic index (PI) was determined using O. aries erythrocytes. Chickens were divergently selected into high (HPPG) and low (LPPG) phagocytosis product groups based on monocyte/macrophage phagocytic capacity at 16 weeks of age (wk). Production traits, immune-related gene expression, oxidative stress-related markers, and pathogen-clearance ability were compared between groups using Student's t-test.

RESULTS

PP measured by the MTT-HCT-8 method was significantly correlated with PP or PI using the other methods (P < 0.05, R 2 > 0.70). HPPG hens showed significantly higher laying rates at 40 and 60 weeks and greater hatch weight than LPPG hens (P < 0.05), whereas fertility, hatchability, or semen quality did not differ between groups. HPPG birds exhibited higher interferon-gamma receptor (IFNGR) and Toll-like receptor 2 (TLR2) expression and, after S. pullorum challenge, showed reduced tumor necrosis factor α (TNF-α) and increased microtubule-associated protein 1 light chain 3 alpha (LC3A) expression (P < 0.05), indicating enhanced pathogen clearance and autophagy without exacerbating oxidative stress or inflammation.

CONCLUSION

Selecting for proper high phagocytic capacity (with a preliminary estimated PP range of 1.58-2.74) improves resistance in layer chickens reared antibiotic-free without reducing productivity and exacerbating oxidative stress or inflammation. These findings support phagocytosis-based phenotyping as a potential balanced-breeding strategy consistent with One Health goals for sustainable poultry production.