Thumps is sometimes seen in standardbred horses post-race and post-exercise.

Thumps is the colloquial name for synchronous diaphragmatic flutter (SDF). The flank muscles are seen to contract (flutter) in a regular manner, because the muscles are contracting at the same time as the heart.

Muscle contractions can appear on one side or both and can range from barely detectable to an obvious thumping sound (hence the name).

It is important to realise that if the flank muscles are contracting so is the diaphragm.  The diaphragm is the large muscle that separates the abdomen from the chest cavity. The muscle contractions are a symptom of a serious underlying disease process.

Horses developing thumps consistently have low potassium, low chloride and alkaline blood. They often have low calcium levels too. All these changes are consistent with acute deranged electrolyte balance.

These derangements are usually caused by acute dehydration/exhaustion or recent inappropriate electrolyte administration. Longer term over-supplementation with calcium and inappropriate bicarbonate administration in dehydrated or electrolyte depleted horses can induce thumps.

Mild cases of thumps will recover with rest and free access to water and hay. More severe cases require intravenous administration of calcium solutions. This should only be performed by a vet who can constantly monitor the heart at the same time, because this sort of supplementation can induce heart failure.

Failure to manage the underlying electrolyte derangement can result in laminitis, acute muscle damage (including to the heart) and renal failure.

Horses developing thumps post-race should be given access to food and water immediately. They can be expected to be stood down from racing pending electrolyte analysis and dietary review.

Preventing thumps is a matter of balancing dietary rations, ensuring the horse is fit enough for the level of work it is doing and maintaining adequate hydration. Horses that have previously developed thumps are more likely to do so again. Their electrolyte balance, hydration status and dietary calcium intake needs to more closely monitored than horses that have not previously experienced this problem.