By Mark Andrews

Horses undertaking strenuous or prolonged exercise in hot and humid environments may produce heat more quickly than they can lose it, putting them at risk of postexercise exertional heat illness. Early detection of the clinical signs of exertional heat illness and adequate treatments are important to prevent severe hyperthermia and irreversible thermal damage.

Investigations into heat production and cooling require a way to accurately monitor body temperature. Ideally, this should be easy and safe to do in an excitable horse after exercise. In practice, reading the rectal temperature with a thermometer is a common starting point - but may not be ideal, particularly if repeated readings in excited horses are required. The gold standard for monitoring is to record the central venous temperature (CVT) using a thermocouple introduced into the jugular vein.  

Horses cool themselves primarily by sweating, but in hot, humid weather sweat evaporation doesn’t allow sufficient cooling, and horses can become overheated, with serious consequences. A hot horse can be cooled two degrees in ten minutes by pouring on water and scraping it off, then repeating the process. Photo: Shutterstock/Kertu

Temperature sensitive microchips - percutaneous thermal sensing microchip (PTSM) - can be used to measure tissue temperature in a non-invasive manner. But how does the site of implantation affect the accuracy?

Researchers at the School of Agriculture and Food Sciences, and the School of Veterinary Science, at the University of Queensland, Australia investigated the use of PTSMs for monitoring temperature in horses after strenuous exercise.

Nuchal ligament in the neck (indicated by the yellow line) Photo: Canstock/Wehzet

Microchips used for identification purposes are generally implanted in the nuchal ligament in the neck. In a preliminary study, the research team found that temperature recorded by a PTSM chip implanted in the nuchal ligament correlated poorly with the CVT during and immediately after exercise. They suggest that this was probably due to the poor vascular supply of the nuchal ligament compared to other muscles.

The researchers also found poor correlation between rectal temperature and CVT immediately after exercise, and for at least eight minutes after exercise. Because of this, and for safety reasons, they suggest that rectal temperature should not be used to measure temperature after exercise.

Of the implantation sites they tested, the researchers found that the most reliable was the pectoral muscles, which closely matched the CVT, followed by the gluteal muscles and the splenius muscle.

Researchers found that the pectoral muscles were the most reliable site for implantation of the PTSM chip to accurately measure tissue temperature. Photo: Shutterstock/Cheryl Ann Quigley

They conclude that PTSMs provide a simple, safe, quick, accurate, and non-invasive way of measuring body temperature of horses immediately after high-speed exercise. They recommend further studies to validate this method under field conditions and in equine athletes working in extreme environments and intensive activity in various equestrian sports.

For more details, see: The Use of Percutaneous Thermal Sensing Microchips for Body Temperature Measurements in Horses Prior to, during and after Treadmill Exercise

Published with the kind permission of Mark Andrews, Equine Science Update.

Main photo: Shutterstock/Rolf Dannenberg