Equine 'Thumps' Are More than Mere Hiccups

One of the best known cures for relieving someone of the hiccups is a good, old-fashioned scare. However, what do you do when it seems that your horse has a case of the hiccups? Sneaking up behind a 1,000 pound Thoroughbred and yelling "Boo!," is not advisable for several reasons. For one, you might get a surprise of your own.

The medical term for the noise we commonly refer to as hiccups is synchronous diaphragmatic flutter or singultus. But in horses it has been specifically called thumps since 1831 when a veterinarian first reported a thumping noise coming from the abdomen of a horse that just ran 13 miles.

"Thumps in and of itself is not a problem," said Cristobal Navas de Solís, LV, an equine internal medicine resident at the University of Illinois Veterinary Teaching Hospital. "But if a horse does have thumps, there is usually an underlying cause that needs to be treated."

Many horses that present with the anomaly are endurance athletes that have an electrolyte imbalance and significant fluid loss after an exhaustive workout. For example, thumps is common in Arabian horses competing in long distance races that last 25, 50, or even 100 miles.

"Typically these patients are dehydrated and have low blood calcium levels," mentioned Navas de Solís, "but once you treat the underlying problem the thumps usually disappear on their own."

Thumps in horses, and hiccups in humans, although both referred to as synchronous diaphragmatic flutter to the medical experts in each field, are slightly different variations upon the same theme. For one, hiccups in humans are not commonly associated with electrolyte imbalances.

Secondly, the location from which we hear the characteristic noise coming also differs in horse and man. The "hic" we hear in humans is caused by the closure of the vocal chords after the diaphragm spasmodically contracts, quickly inflating the lungs. In horses, however, veterinarians and owners that have witnessed the ailment can attest that the abnormal noise comes from the animal's side.

Low blood calcium levels are the classic abnormality associated with thumps. This may make the phrenic nerve, which runs along both sides of the heart and controls diaphragm movements, more easily excitable. But it is also a good idea to check all electrolyte levels, especially magnesium, potassium, sodium, and chlorine.

In a typical scenario with a dehydrated horse and abnormal electrolyte levels, the phrenic nerve might begin to fire at the rate at which the atria of the heart contract. In short, the nerve is inappropriately obeying firing instructions from the heart, instead of the brain, to control diaphragm movements.

"Usually we see the horse's abdomen contract 40-50 times per minute," said Navas de Solís. Typically, each contraction occurs at the same time the heart beats, but in rare cases that does not always happen, nor do the thumps have to occur on both sides of the horse.

Although hiccups in humans are quite harmless, thumps in horses are usually linked to an abnormality that warrants attention. If you hear the telltale sounds--and don't suspect your horse has merely gotten into the Kentucky bourbon--contact your veterinarian as soon as possible.--Ashley Mitek, University of Illinois College of Veterinary Medicine

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