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

## TL;DR

This study compares lung structure and health in pigs raised under different management systems, finding that free-range pigs have healthier lungs while beta-agonist-free rearing leads to more fibrosis and inflammation.

## Contribution

The study provides the first quantitative, lobe-specific histomorphometric comparison of pulmonary remodeling in swine under different management systems.

## Key findings

- Beta-agonist-free rearing pigs showed thicker alveolar walls, higher fibrosis, and increased macrophage density in middle and caudal lobes.
- Free-range pigs exhibited preserved pulmonary architecture with thinner alveolar septa and lower fibrosis indices.
- Hygienic management resulted in intermediate lung parameters, suggesting balanced structural adaptation.

## Abstract

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.

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).

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.

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.