When you are moving, a vacuum is created by the trailer resulting in the exhaust fumes being "sucked" into the cabin through the vents, cracks and open spaces, creating a concentrated toxic environment. Exhaust fumes contain Carbon Monoxide (CO) which causes a variety of health problems in horses and even death. Depending on the levels of toxic and irritant substances breathed in from the air, horses can develop symptoms ranging from a mild headache with lethargy and poor performance, to pneumonia or travel sickness. Have you noticed your horse with any of these symptoms? CO enters the bloodstream and impairs exercise capacity, visual perception, dexterity, learning functions and causes a wide range of respiratory problems. Exhaust fumes contain many individual gases and particulate matter that range form mildly toxic to deadly. Inhalation of these gases leads to a wide range of symptoms that range from mild nausea and headaches to pneumonia, chronic respiratory disease, or even sudden death from the inhalation of Carbon Monoxide.