Comparative lobe-specific histomorphometric evaluation of pulmonary architecture, fibrosis, and alveolar macrophage distribution in swine raised under different management systems.

BACKGROUND AND AIM: Swine housing and management systems strongly influence respiratory health through their effects on air quality, ventilation, and environmental exposure. However, quantitative, lobe-specific evidence describing how different management systems affect pulmonary microarchitecture remains limited. This study aimed to compare alveolar structure, fibrosis, collagen deposition, and alveolar macrophage distribution in swine raised under hygienic, beta-agonist-free rearing, and free-range systems.

MATERIALS AND

METHODS

Fifteen clinically healthy male crossbred (Large White × Landrace) swine were allocated to three management systems (n = 5 per group): hygienic, beta-agonist-free rearing, and free-range. Lung samples were collected from the right cranial, middle, and caudal lobes following humane slaughter. Sections were stained with Masson's trichrome for collagen visualization. Quantitative histomorphometric analyses included alveolar wall thickness, alveolar space area, fibrosis distribution (%), semi-quantitative fibrosis score, collagen intensity (mean gray value) in bronchial hyaline cartilage, and alveolar macrophage density (AMD). Image analysis was performed using ImageJ, and observers were blinded to group allocation. Data were analyzed using one-way analysis of variance with Tukey's post hoc test (p < 0.05).

RESULTS

Marked lobe-specific differences were observed among management systems. Swine raised under beta-agonist-free rearing exhibited significantly thicker alveolar walls, reduced alveolar space area, higher fibrosis distribution and scores, increased collagen accumulation, and elevated AMD, particularly in the middle and caudal lobes. In contrast, free-range swine demonstrated thinner alveolar septa, wider alveolar spaces, lower fibrosis indices, and reduced macrophage infiltration, indicating preserved pulmonary architecture and reduced inflammatory remodeling. The hygienic group consistently showed intermediate values across most parameters, reflecting balanced structural adaptation under controlled housing conditions.

CONCLUSION

Swine management systems are associated with distinct patterns of pulmonary structural and immunological adaptation. Beta-agonist-free rearing was linked to early fibrotic remodeling and increased immune activation, whereas free-range management supported structural preservation and lower inflammatory burden. This study provides the first quantitative, lobe-specific histomorphometric comparison of pulmonary remodeling across different swine management systems, offering valuable insights for welfare-oriented and sustainable livestock production strategies.