- Incomplete expansion of the lung at birth (congenital) or collapse of previously air-filled lung (acquired)
- Failure of lung tissue to expand at birth
- Ranges from total in stillborn animals to patchy areas in the case of weak neonates, showing more in the dependant lobes in recumbency
- The neonatal respiratory syndrome
- Best documented in foals but reported in other species
- Also features extensive atelectasis
- These animals are called 'barkers' due to the noise made during forced expiration
- Gross pathology:
- Red fleshy appearance to the affected part, depressed below the surface if there are adjacent normal aerated areas
- Cut surface oozes blood, perhaps some froth in 'barkers'
- Affected areas sink or are submerged in fixative
- Micro pathology:
- Close approximation of capillary walls
- Little normal alveolar pattern
- 'Barkers' may have a proteinaceous fluid in alveoli with hyaline membranes in lower airways
- Cause:
- In weak neonates -inadequate respiratory effort or damage to the respiratory centres in the brain, aspiration of amniotic fluid or meconium
- In 'barkers'- defective production of surfactant by the Type 2 alveolar epithelium
- Foals that survive may have hypoxic damage to their brain, walk aimlessly and lack normal sense of fear - "wanderers"