Minimum carbon dioxide is a key predictor of the respiratory health of pigs in climate-controlled housing systems.

Background: Respiratory disease is an economically important disease in the swine industry. Housing air quality control is crucial for maintaining the respiratory health of pigs. However, maintaining air quality is a limitation of current housing systems. This study evaluated the growth and health parameters of pigs raised under different environmental conditions and identified key environmental variables that determine respiratory health. Eighty (Largewhite × Landrace) × Duroc crossed growing pigs (31.71 ± 0.53 kg) were equally distributed into two identical climate-controlled houses with distinct environmental conditions (CON = normal conditions and TRT = poor conditions). Two-sample tests were performed to compare the means of the groups, and a random forest algorithm was used to identify the importance scores of the environmental variables to respiratory health.

Results: Pigs in the TRT group were significantly exposed to high temperatures (28.44 vs 22.78 °C, p < 0.001), humidity (88.27 vs 61.86%, p < 0.001), CO₂ (2,739.93 vs 847.91 ppm, p < 0.001), NH₃ (20.53 vs 8.18 ppm, p < 0.001), and H₂S (14.28 vs 6.70 ppm, p < 0.001). Chronic exposure to these factors significantly reduced daily feed intake (1.82 vs 2.32 kg, p = 0.002), resulting in a significant reduction in average daily gain (0.72 vs 0.92 kg, p = 0.026), increased oxidative stress index (3.24 vs 1.43, p = 0.001), reduced cortisol levels (2.23 vs 4.07 mmol/L, p = 0.034), and deteriorated respiratory health status (74.41 vs 97.55, p < 0.001). Furthermore, a random forest model identified Min CO₂, Min NH₃, and Avg CO₂ as the best predictors of respiratory health, and CO₂ was strongly correlated with NH₃ and H₂S concentrations.

Conclusions: These findings emphasize the critical importance of proper environmental management in pig farming and suggest that regular monitoring and control of either CO₂ or NH₃, facilitated by environmental sensors and integration into intelligent systems, can serve as an effective strategy for improving respiratory health management in pigs.