Which nutritional disorder is known to affect the respiratory system of horses?

Heaves, also known as recurrent airway obstruction (RAO), is a chronic respiratory condition in horses primarily caused by allergic reactions to environmental allergens, frequently found in hay, bedding, or dust. The disorder leads to inflammation and narrowing of the airways, resulting in difficulty breathing. Symptoms can include a persistent cough, increased respiratory effort, and exercise intolerance.

This condition is related to a horse's nutritional environment, particularly how the forage (such as hay) is stored and handled. Poorly stored hay that becomes moldy or dusty can trigger heaves, highlighting the connection between nutrition, environment, and respiratory health.

Other options like rhabdomyolysis are related to muscle issues typically induced by exercise or dietary imbalances, pneumonia is an infection in the lungs generally not associated with nutrition but rather with bacterial or viral pathogens, and hypoproteinemia refers to low protein levels in the blood which can be caused by various health issues but does not specifically target the respiratory system.