What condition is suggested by bright red mucous membranes and respiratory distress in a horse?

Bright red mucous membranes in a horse, alongside respiratory distress, strongly suggest cyanide toxicity. This is due to the way cyanide affects the body; it inhibits cellular respiration, leading to an inability of cells to utilize oxygen. As a result, despite having sufficient oxygen in the blood, cells are unable to perform their functions, causing a characteristic bright red coloration of the mucous membranes due to the presence of oxygenated blood that is not being utilized effectively.

In contrast, conditions such as choke may cause respiratory distress, but they typically do not lead to bright red mucous membranes. Usually, choke is associated with difficulty swallowing and potentially a distended esophagus, not specific changes in mucous membrane color. Chronic Obstructive Pulmonary Disease (COPD), though it involves respiratory issues, tends to manifest differently with signs like coughing and exaggerated breathing rather than a change in mucous membrane color. Walnut toxicity is not commonly linked to these symptoms either, as it primarily causes neurological and gastro-intestinal signs rather than respiratory distress with striking changes in mucous membranes.