2021 AERC Convention Notes: Dr. Langdon Fielding on Electrolyte Problems in Endurance Horses

I love seminar notes. Rarely can I take the time to go back and watch an entire presentation, but I do re-read my scribbles for a refresher on the key points. I hope that sharing them here will be helpful to you as well. 
 
Of course, I can’t possibly share all the details from this stellar session by Langdon Fielding, DVM, MBA, DAVECC, DACVSMR, and self-proclaimed electrolyte fanatic. To really take advantage of his generosity, register with AERC to access the 2021 Unconventional Convention content, which will be available through the end of March 2021.

Sodium in Endurance Horses

Dr. Fielding began by sharing a typical lab panel taken from an “Ain’t Doin’ Right” horse at an endurance ride. The panel showed higher than normal sodium and lower than normal potassium, chloride, and calcium. He posed the question: Is the problem here too much sodium or too little water?

This horse’s sodium was high. How did it get that way? Either he was given too many electrolytes, or he lost more water through sweat then he replaced by drinking. He may also have been  dehydrated before the start.
 
If the horse’s lab panel had shown low sodium levels instead, Dr. Fielding would have been asking if we didn’t administer enough electrolytes, or if the horse actually drank too much. He observed that although it is possible (such as after a tough haul), horses rarely begin rides deficient in electrolytes.

The concentration of electrolytes in a horse's blood is different than the concentration of electrolytes in his sweat.
Potassium and chloride are much higher in sweat than in blood. Calcium and magnesium are lower in sweat than in blood, though the difference is less extreme. Sodium levels are similar in blood and sweat.

~ Dr. Langdon Fielding on Electrolytes in the Endurance Horse, AERC Convention, March 6, 2021

​Because sodium is all about the balance between electrolytes and water, identifying which side of the equation (sodium or water) got the level out of whack is key to preventing a repeat performance.

Potassium in the Endurance Horse

Moving on to potassium, Dr. Fielding said so much of this electrolyte is lost in sweat that low levels are common on lab panels taken during endurance events. Some horses tolerate low potassium better than others, and it’s not always problematic. However, low potassium is common in horses that are struggling or require treatment.
 
Dr. Fielding added that although weakness is a classic symptom of low potassium, this can be hard to differentiate from normal fatigue in an endurance horse.

Calcium and Thumps in the Endurance Horse

Dr. Fielding noted that although calcium is clearly tied to muscle and heart function, it is less consistently associated with endurance horses that are having trouble.
 
Low calcium, typically in addition to loss of potassium, chloride, and sodium (in Dr. Fielding’s words, "lots of electrolyte abnormalities colliding"), can contribute to synchronous diaphragmatic flutter, or thumps. Interestingly, thumps may be observed in a horse that is otherwise fine, as well as in a horse that is exhausted.
 
Dr. Fielding noted that feeing a horse alfalfa (which is high in calcium) can help thumps resolve within an hour or two, but cautioned that giving electrolytes to the horse could be risky if the horse is dehydrated. He said a vet would generally treat thumps with IV fluids including calcium.

Although not well documented, it is possible that a genetic component predisposes some horses to thumps.
​~ Dr. Fielding in response to an audience question

Dr. Fielding emphasized the importance of determining why a horse prone to thumps is affected. Future episodes may be preventable through changes to the horse’s electrolyte protocol.

It is possible – though this has not been rigorously tested – that feeding a low calcium diet during conditioning, then offering alfalfa just before the ride, can help prevent thumps. Dr. Fielding cautioned against doing the reverse; that is, eliminating alfalfa at a ride if a horse is accustomed to consuming it.

Final Words

Dr. Fielding wrapped up his presentation with a reminder that problems in endurance horses aren't always about electrolytes…and when they are, the answer isn’t always about changing products or administering more. 

Q&A with Dr. Fielding

Q. Where do you start on developing an electrolyte strategy?

A. As a starting place in a horse that isn't having problems, try 1/2 tube of electrolytes per vet check.

Q. Should we preload with electrolytes?
​
A. Dr. Fielding is neither for nor against this practice. Additional research on the subject is needed.

Riders should do their best to ensure that horse are hydrated before the ride and that sweat losses (both electrolytes and water) are replaced during the ride. If a particular horse is having issues, the rider should work with her vet on a targeted strategy.

​There was so much more to this presentation! For example, did you know that blood gets less acidic as chloride is lost? Or that ammonia is an electrolyte?

I highly recommend listening to the full talk. Access it by registering for the Unconventional Convention on the AERC website. Registration should be available by March 15, 2021, giving you access through the end of the month.

Did you get a chance to listen to Dr. Fielding's talk? What did you find most interesting?

You might also like: Dr. Stephanie Seheult on How Your Body Works with your Horse

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