The more your horse sweats, the greater the risk of electrolyte imbalance and thumps.

By Kathy Smith

Also known as synchronous diaphragmatic flutter, thumps looks alarmingly like hiccups in humans — a rhythmic “thump” or twitch of the horse’s flank that often matches its heartbeat. While human hiccups are harmless, thumps signals an underlying electrolyte imbalance that can affect performance and well-being.

The condition occurs when the phrenic nerve, which controls movement of the diaphragm, becomes overly excitable. Instead of responding to signals from the brain, it starts reacting to impulses from the atria of the heart, causing the diaphragm to contract in sync with every beat — sometimes as often as 60 times per minute.

Why Thumps Happens

Electrolyte imbalances are the primary culprit. When horses sweat heavily during endurance exercise, hot weather, or prolonged work, they lose essential minerals such as calcium, sodium, potassium, magnesium, and chloride. Dehydration, diarrhea, or kidney dysfunction can worsen the loss, while diuretics such as Lasix®, sometimes used in racing, may further deplete electrolytes.

Alkalosis (excessive blood alkalinity) resulting from low ionized blood calcium can cause the phrenic nerve to become hyperexcited, triggering thumps, explains Kathleen Crandell, Ph.D., equine nutritionist with Kentucky Equine Research. Treatment consists of electrolyte replenishment, and if severe enough, intravenous calcium may be required.

Treatment and Prevention

Thumps usually resolves once electrolyte levels are restored. However, the best strategy is prevention. Horses that sweat heavily during endurance events or long rides should receive electrolyte supplementation before, during, and after exercise to replace key minerals lost through sweat. Clinical studies show it is beneficial to administer electrolyte solutions about every 20 kilometres during long-distance races.

Ironically, horses that eat a great deal of alfalfa, which is high in calcium, may have more calcium lost during sweating and experience worse dehydration. Reducing calcium intake a few days before competition can help maintain proper calcium balance. Always ensure access to clean water and encourage hydration.

If thumps persist even after electrolyte replacement, consult your veterinarian. Though usually temporary, the condition can indicate deeper metabolic or organ-related issues. With attentive care and proper nutrition, horses can recover quickly — and stay thumps-free on their next ride. 

Related: How to Test Your Horse for Dehydration

Related: The Science of Sweat: Supplementing Electrolytes for Better Equine Health and Performance

More by Kathy Smith

With files from FEI, Kentucky Equine Research

Main image: Alamy-Sandy Young