Development of pulmonary arterial hypertension and diffuse alveolar damage in 2-month old Holstein dairy calves following an acute episode of bloody scours

Background: The goal of this study was to evaluate the effect of hypoxia on intestinal permeability and cardiopulmonary physiology in 2-month old calves.Methods: Calves were exposed to normoxic (975 m altitude; controls) or hypoxic (4,570 m altitude) conditions for 2 weeks. Pulmonary arterial pressures and intestinal permeability to mannitol and lactulose were assessed on Days 0 and 14. Calves were euthanized on Day 15. Two control calves shed occult fecal blood on Day 3; consequently, all calves were treated for coccidiosis.Results: Control calves tended to have greater mean pulmonary arterial pressure than hypoxic calves at Day 0 (P =0.17), but there was no difference between groups at Day 14 (P =0.47). On average, mean pulmonary arterial pressure increased by 16 ± 2 mm Hg from Day 0 to 14 (P <0.001). Serum lactulose was 0.8 ± 0.4 mg/L greater in the control group than the hypoxic group on Days 0 and 14 (P =0.08). Serum mannitol was 2.0 ± 0.8 mg/L greater in control calves than hypoxic calves on Day 0 (P =0.009) but there was no difference between groups at Day 14 (P =0.61).Conclusions: Hypoxia did not affect intestinal permeability, but the results were confounded by intestinal disease. Interestingly, the two calves that had bloody scours had the greatest pulmonary arterial pressures and diffuse alveolar damage. The findings of this study provide preliminary evidence that intestinal disease may contribute to the development of pulmonary diseases in cattle.