Fatigue and Exercise in Horses

Any animal will get tired when exercised for too long or too hard. Fatigue, however, is the inability to continue on. When fatigue happens, it means your horse has already been worked too hard and should not be pushed any further. While some symptoms of fatigue are mild, such as sweating and panting, there are more moderate and severe symptoms that can follow such as dehydration, exhaustion, respiratory related problems, and even death. Fatigue can affect your horse physically, mentally, and metabolically. The best form of treatment is prevention, however rehydrating your horse with the proper fluids, altering his exercise habits, and ensuring he recovers completely before working him again are all important forms of treatment as well.

Exercise related fatigue is a very serious condition in any animal species. In horses, it can occur on a physical level and metabolic level. If fatigue sets in, you will need to seek immediate veterinary attention for your horse.

Symptoms typically occur after prolonged exercise. Symptoms may include:

• Panting
• Sweating
• Dehydration
• Acid-base imbalances
• Electrolyte imbalances
• Exhaustion
• Decreased motivation
• Respiratory issues
• Lethargy 
• Tiredness 
• Loss of muscle coordination 
• Death 

Types        

There are two types of fatigue a horse can suffer from. Peripheral fatigue is known as fatigue secondary to altered muscle function. Central fatigue is an alteration in the CNS signals within the body by modifying the action potential of the motor neurons. Peripheral fatigue is seen more on the metabolic level while central fatigue is seen as more clinical signs of tiredness and related symptoms.

The main cause of peripheral fatigue is the failure of ATP to resynthesize in addition to accumulation of inorganic phosphate ions and ADP. This means the metabolism of the muscle is abnormal and therefore causes metabolic discrepancies. Central fatigue is mainly caused by change of efficiency within the motor neurons of the body causing them to not work as well as they should.

When your veterinarian first arrives, she will begin by collecting a history from you and will perform a complete physical exam. A thorough history from you as the owner can give her ideas to what ailment your horse may be suffering from. Describe his symptoms and his behavior to her so that she can begin to rule out other probable causes. By performing a complete physical exam, it allows her to check out every aspect of your horse. Some symptoms may be obvious, such as pain or sluggishness, but some symptoms may not be which will lead to diagnostic testing.

To properly diagnose your horse with fatigue, the veterinarian will want to run multiple tests. These tests will include metabolic tests and blood work. Since peripheral fatigue affects many metabolites, tests can show if your horse is experiencing the typical metabolic symptoms or not. Typical test results of a horse suffering from fatigue may include abnormal ranges of glycogen levels, pH, creatine phosphate ratio, inorganic phosphate and more. The veterinarian may run serum tests to check your horse’s serum biomarkers which will include lymphocytes, lactate, ammonia, and oxidative damage to name a few. Blood work may consist of a complete blood count and chemistry panel to get a broad overlook of how the body is functioning as a whole.

The information you relay to the veterinary team, the examination, and the results of your horse’s lab work will give the information needed to make a proper diagnosis.

The results of the diagnostic tests will determine the course of treatment. If there is an actual medical condition underlying your horse’s fatigue, then it will be treated appropriately. However, if it was due simply to malnutrition, lack of water, and not enough rest, it will be entirely up to you to change his lifestyle. 

Your veterinarian will also thoroughly go over the nutrition needs of your horse and how to keep him hydrated when exercising. She will likely come up with a plan on how to safely exercise him in the future so as to prevent this from occurring again. 

When offering him water for rehydration, studies have shown a saline solution of 0.9% NaCl is best. This solution allows your horse’s body to maintain a higher plasma sodium concentration and body weight recovery occurred faster than with normal water.

The source of your horse’s fatigue and the treatment the veterinarian implements will determine his recovery. If your horse is suffering from fatigue and you do nothing or push him even further, consequences may be fatal. However, if you seek veterinary attention immediately and do the treatments she recommends, his prognosis of a recovery is good.