Currently, research is focusing on the health of the horse's respiratory system as a primary factor for performance. An adult horse's lungs can be negatively affected by exposure to low levels of ammonia, especially if the exposure occurs at a young age.

When a horse urinates, urea is expelled in the urine which is broken down into ammonia gas. This pungent smelling gas is caustic and can burn the delicate tissues of the respiratory tract and eyes, as well as the soft tissue around the hooves.

The United Food and Commercial Workers warns that extended exposure to ammonia fumes can cause permanent lung and eye damage. Initial exposure to ammonia causes irritation and burning eyes, nose and throat, nausea, vomiting and dizziness. Continued exposure to high ammonia levels may dull the body's sensitivity to ammonia. This lack of sensitivity can mean that even horses not experiencing symptoms may still be exposed to dangerous levels of ammonia.

Foals are extremely susceptible to high ammonia levels because they spend so much time on the floors of the stalls, where the ammonia levels are the highest. A University of Kentucky study found ammonia readings at the floor level of stalls reached 228 ppm (parts per million) in some barns. Most people can smell ammonia when levels reach 20-30 ppm.

Currently, a minimum acceptable level of ammonia for horses and foals has not been established. However, research on the effects of ammonia exposure on calves has indicated that levels of low as 10 ppm may be the cause of health problems. Therefore, if horses are being exposed to those levels or higher, the probability of damage is great.

Some researchers suspect that heaves (COPD) may be avoidable if horses are not exposed to high levels of ammonia, especially when they are foals. Horses with COPD have increased respiratory problems when they are housed in stalls with high levels of ammonia.

A study was conducted in a 40-stall boarding facility during February and March of 2007 to determine the effects of Stall Fresh on the production of ammonia gases. The results below show a reduction in ammonia of up to 50%.