Microchips implanted in horses show promise as a simple, safe, and accurate way of measuring body temperature, with the potential to head off heat-related illness, according to researchers.
Temperature-sensing microchips inserted into the muscle through the skin provided readings that correlated well with the core body temperature of horses before, during and after exercise.
During exercise, horses produce heat from working muscles which can accumulate. Conduction, convection, radiation, and evaporation are the main heat transfer mechanisms to control body temperature.
“Horses that undergo strenuous exercise in hot and humid environments may have heat production that exceeds their ability to dissipate the heat,” Hyungsuk Kang and his University of Queensland colleagues wrote in the journal Animals.
This puts horses at risk from exertional heat illness, possibly leading to heat shock and death.
To avoid this, many Thoroughbred racehorses are cooled after racing by water, fans, or a combination of both.
The researchers said early detection of the clinical signs of exertional heat illness and adequate treatments are important to prevent potentially irreversible damage.
The researchers noted that thermal-sensing microchips have been used in several horse studies, but they wanted to take this further, exploring the chips’ performance before, during and after exercise.
An experiment was devised using eight unconditioned adult horses, comprising four Thoroughbreds and four Standardbreds, all with the research herd at the University of Queensland.
Thermal sensing microchips which each contained a passive transponder were implanted two weeks before the experiment.
The microchips were inserted perpendicular to the skin to the maximum depth allowed by the 12-gauge needle assembly containing the transponder.
The first two horses had chips installed into the nuchal ligament of the neck, halfway between the poll and the withers. A preliminary study involving these two horses showed a poor correlation between the microchip readings and the animals’ core temperature, most likely related to the poor blood supply of the nuchal ligament compared to other muscles.
The study was therefore modified, with all eight horses (including the first two) being chipped in the right splenius muscle of the neck, the right pectoral muscle of the chest, and the right gluteal muscle area of the hindquarter.
For the experiment, a probe monitored the central venous temperature — considered to be the gold standard for assessing core body temperature.
Rectal temperature was also monitored.
All horses were familiarized with the treadmill before the experiment, in which the temperature of each implant was evaluated in each phase (before, during, and immediately after the standardised treadmill exercise session).
Combining all phases, the researchers found strong positive correlations between temperature readings from all the muscle sites with the central venous temperature.
Taken individually, the chip in the pectoral muscle proved most reliable, providing a valid estimation of the core body temperature.
“These results are promising in regards to finding a simple, safe, quick, accurate, and noninvasive method to measure the body temperature of horses immediately after high-speed exercise,” the study team said.
“Future studies are needed to validate this method under field conditions and in equine athletes working in extreme environments and intensive activity in various equestrian sports.”
Further development and application of the technology might help in the detection of postrace exertional heat illness in equine athletes, they said.
Heat-sensing microchips would also aid further investigation into the most efficient cooling techniques for horses and, ultimately, the best procedures to decrease the prevalence of exertional heat illness at the racetrack.
They said the microchips proved to be a reliable way to measure body temperature. However, the optimal location within horses needs to be determined.
Discussing their findings, the authors said: “Although the different muscle sites used in the present study actively engage differently during exercise, temperature change followed a very similar pattern, with all rising rapidly to exceed rectal temperature.”
They said implantation of the microchips into muscle was minimally invasive, requiring only the injection of the microchip through a large gauge needle. “After initial implantation, measuring body temperature is completely noninvasive.”
No adverse reactions were observed concerning the microchip implantation site, and the procedure was well tolerated by all horses. No movement of the microchips was observed during follow-up. The horses showed no limitations to movement by having the microchips placed in their muscles.
The study team comprised Kang, Rebeka Zsoldos, Solomon Woldeyohannes, John Gaughan and Albert Sole Guitart, all with the University of Queensland.
Kang, H.; Zsoldos, R.R.; Woldeyohannes, S.M.; Gaughan, J.B.; Sole Guitart, A. The Use of Percutaneous Thermal Sensing Microchips for Body Temperature Measurements in Horses Prior to, during and after Treadmill Exercise. Animals 2020, 10, 2274.