Alteration of growth performance and characterization of pathological lesions in long-term ammonia-exposed pigs

Ammonia (NH₃) is a major cause of odor emissions from swine farms, and exposure to high concentrations of NH₃ in short-term periods has been reported to cause respiratory and systemic disorders in pigs. However, the impact of long-term NH₃ exposure on pig health and productivity remain unknown. This study aimed to assess the impact of long-term NH₃ exposure on growth performance and pathological outcomes in pigs. Pigs were reared in the treatment room [34.8 mg/m³ NH₃ concentration (50 ppm); TRT group, n = 40] and the control room [5.6 mg/m³ (8 ppm); CON, n = 40]. The experimental period was 107 days (from weaning piglets to market age). Our findings revealed that long-term NH₃ exposure results in severe respiratory and systemic pathological lesions, including chronic tracheitis, epithelial metaplasia of the trachea, severe interstitial pneumonia, myocarditis, and interstitial nephritis. In addition, the TRT group exhibited reduced productivity, with two deaths, indicating that uncontrolled NH₃ concentrations on pig farms could be linked to a decline in growth performance and even death. Transcriptomic analysis revealed significant changes in immune and inflammatory pathways in lung from TRT pigs, including dysregulated cytokine signaling and incomplete inflammatory responses. The enrichment of DEGs in pathways, such as Cytokine-cytokine receptor interaction, JAK-STAT, and Toll-like receptor signaling, indicated chronic NH₃ exposure disrupted immune homeostasis, contributing to chronic inflammation and impaired tissue repair. In conclusion, this study provides valuable insights into the detrimental effects of NH₃ exposure on pig health and productivity under farm conditions.