Morphometric examination of the equine adult and foal lung.

This research aimed to understand the standard structural characteristics of a healthy horse’s lungs to provide baseline information for studying lung inflammation associated with equine diseases such as Rhodococcus equi infection. The analysis showed that postnatal lung development in foals is driven by alveolar expansion in concert with blood vessel formation.

Methodology

• The researchers studied healthy adult horse lungs and those of one-day (5 samples) and thirty-day-old (5 samples) foals.
• The left lung was fixed via intrabronchial instillation of glutaraldehyde/paraformaldehyde fixative and sampled based on a fractionator design approach.
• The sampled lung tissues were then embedded in glycol methacrylate for further examination.

Quantitative Analysis

• The study divided the lung tissue into two categories, parenchyma (functional tissue in the lungs involved in gas exchange) and non-parenchyma.
• The median density of parenchymal tissue was calculated and found to be 81.0%, 84.4%, and 93.7% in one-day-old foals, thirty-day-old foals, and adult horses respectively.
• The volume density of alveolar airspace (space within the lungs dedicated to gas exchange) per lung were 45.9%, 55.5%, and 66.9% in one-day-old, thirty-day-old, and adult horse lungs, respectively.

Morphometric Findings

• The median alveolar surface area increased with age, and it was found that the average distance within acinar airspaces also increased with age.
• Alveolar surface area was more significant than endothelial surface area within each lung, thus indicating more surface area available for gas exchange.
• The ratio between alveolar and endothelial surface density remains steady with age, suggesting constant lung tissue remodeling for efficient gas exchange.
• The median endothelium surface area, which denotes the surface area covered by cells lining the blood vessels, amounted to 106.2 m2, 147.5 m2, and 430 m2 in one-day, thirty-day, and adult lungs, respectively.

Overall Conclusion

• The research concluded that in foals, the lung is functionally developed and postnatal lung development is driven primarily by alveolar expansion and angiogenesis (formation of new blood vessels), thus ensuring efficient mechanisms for oxygen-carbon dioxide exchange in the lungs.