What is “The Thumps”?

The Thumps, more technically known as Synchronous Diaphragmatic Flutter is the excitation of the diaphragm. It’s similar to hiccups in humans and can be seen as twitching or spasms of one or both flanks. In some cases, a loud thump can be heard coming from the horse’s chest.

What causes it?

The diaphragm is a thin muscle separating the horse’s chest and abdomen. It is controlled by the phrenic nerve, which is important for regulating the horse’s breathing. Electrolyte (salt) disturbances in the body (particularly abnormalities in calcium, chloride, magnesium, and bicarbonate) can make the phrenic nerve become hyper-excited. This causes it to be more sensitive to the activity in the heart which it runs past. If the nerve conductions are not normal due to the nerve being excited, then the diaphragm begins to vibrate. Meaning that unusual noises or contractions are produced. Because the phrenic nerve runs over the heart, the unusual movements, vibrations, or thumps are a result of the heartbeat, not the breathing cycle.

Increased excitation of the phrenic nerve is most commonly associated with intense exercise. Such as endurance rides or racing as the horse usually sweats a lot, resulting in a loss of electrolytes. 

How serious is it?

Because the condition usually occurs when a horse has been sweating a lot, in most cases the signs resolve once the electrolyte level gets back to normal. Which occurs after the horse eats and drinks normally. In more severe cases, the horse may need to be given electrolytes, either via a stomach tube or in a drip (intravenously). This is in order to correct the imbalances. The prognosis is usually good but a rest period of 7-10 days is often recommended after an episode. This is to ensure that the horse has recovered fully before carrying out intense exercise again.

If the signs don’t go away after the initial treatment, or they start when the horse hasn’t been exercising heavily, you should contact your vet as there may be an underlying problem. The vet will take a blood sample to assess the hydration status of the horse and measure the level of electrolytes. 

Severe diarrhoea and kidney disease can also result in electrolyte imbalances. There are a number of conditions that can lead to a lower calcium level (hypocalcemia). Alfalfa is high in calcium and if a lot of this is fed to a horse before a competition, it may affect the body’s ability to control calcium. This increases the chance of thumps developing.

How can I prevent it?

If your vet has diagnosed a condition that causes hypocalcemia, you should take their advice on treatment and prevention of the signs of thumps. However, if it is something that you are noticing during excessive exercise then there are a few things that you can do to help to reduce the occurrence. 

These include:

  • Developing an exercise plan to gradually increase the workload. This will help to ensure that your horse is fit enough for the work that they will be carrying out.
  • Avoid riding the horse in hot weather if possible. As this will increase the amount of sweating. Therefore resulting in a higher rate of electrolyte loss.
  • Electrolytes can be added to the food or water for a few weeks prior to competition. This ensures that there will be enough in the body at the time of the intense exercise.
  • Ensure that the horse has access to fresh water regularly throughout the competition to prevent dehydration.
  • Electrolytes can also be added to the water during and after the competition to ensure that any losses are replaced. This may also stimulate a normal thirst response.
  • For horses with a diet that is high in calcium, this should be reduced for a few days before the competition to try and stimulate the body to carry out normal calcium regulation.

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