Healthy horses that are used to exercise will rarely appear winded even after a workout due to their large lung capacity. However, there are conditions that can affect a horse’s ability draw an adequate breath. These conditions can cause the horse to breathe rapidly and heavily as they try to recover.
The normal respiration rate of a resting adult horse can vary slightly depending on the size of the animal. The average resting respiratory rate is eight to 16 breaths a minute for a full-size adult horse. Foals and ponies have a higher resting respiratory rate. The respiratory rate of a horse will increase with exercise and exertion just as it does for humans. However, it is important to note that heavy or noisy breathing should not occur in a horse that is in shape and doing work that it is built to do. Being familiar with a horses’ normal respiration will help the owner notice any problems.
Hyperthermia is commonly known as heat stroke. This can occur when a horse is required to do excessive work and is unable to get rid of the generated body heat. Heavy breathing is a common symptom of heat stroke as the horse’s massive lungs work overtime to move oxygenated blood through the body to restore muscles and try to cool down.
When a horse makes a high-pitched wheezing noise at a cantor or gallop, he is said to be “roaring.” This noise is caused by an obstruction of the horse's airway due to the larynx being paralyzed on one side. It becomes noticeable at the faster gaits because of the horse's need to draw in more air. The sound will become noticeably worse as the horse continues to work and becomes fatigued. The paralyzed side of the larynx will start to sag into the airway causing further obstruction. Some horses with a roaring condition are not bothered by it while others will develop severe aversion to any kind of exercise because of it.
A horse that has a displaced soft pallet will make a sound like someone gargling mouthwash when being exercised. This breathing condition occurs when the soft palate flips up at the back of the mouth and blocks the nasal passages. The result is a gurgling sound when the horse breathes out.
Rasping can cause very heavy breathing in a horse that is working because it can greatly reduce the amount of air the horse is able to draw into its lungs. As the horse struggles for more air, it breathes faster. Rasping is a condition that is caused when the muscles that control the pharynx become weak. As the horse breathes in, the walls of the pharynx are stressed. If the muscles that hold the pharynx open are weak, the pharynx will collapse, cutting off the airway.