A horse's body temperature can indicate everything from an internal ailment (such as colic) to an infectious disease to hypothermia. Or it can simply confirm that a horse is healthy and ready for action. While most owners and veterinarians step to the posterior of the horse to determine temperature using a thermometer, researchers from the USDA Animal and Plant Health Inspection Service (APHIS) and Colorado State University are exploring infrared thermography as a viable option for determining temperature.

This noninvasive method could also give authorities an advantage in quickly detecting fever among a group of horses during a time of concern over an infectious disease outbreak, allowing them to intervene promptly and prevent spread of infection.

IRT Image

IRT images of equine eyes are a new method of detecting a horse's body temperature.

According to Shylo R. Johnson, MS, of the National Wildlife Research Center in Fort Collins, Colo., and certified thermographer, there are three tools currently used for determining equine body temperature: rectal thermometers, tympanic infrared thermometers (such a thermometer is inserted into ear and works by measuring the infrared radiation emanating from the tympanic membrane), and thermal microchips.

"These methods of temperature measurements have different limitations such as intolerance to the procedure, time required to obtain the measurement, or the need to have a microchip implanted in each animal and a scanner that can read the microchip," Johnson noted. "A method for measuring temperature that does not have these limitations is infrared thermography (IRT) because it is passive, remote, rapid in the hands of trained personnel, and noninvasive."

Johnson explained that IRT involves a specialized camera that measures the heat an object emits, which it displays as different colors representing different temperatures, adding that the technology is currently used to detect inflammatory responses in horses. In order for IRT to be effective in measuring body temperature, it needs to focus on a surface that correlates with changes in body temperature, such as the eye.

"Our objectives were to determine whether thermographic eye temperatures were associated with body temperatures and could be used to detect febrile (feverish) ponies," Johnson added.

Johnson and colleagues examined 24 Welsh ponies involved in another study in which investigators were testing the efficacy of an equine herpesvirus (EHV-1) vaccine. Because the ponies used in the study were experimentally infected with the virus, the researchers were able to determine when they should begin developing a fever. At that point, they began recording body temperatures measured with rectal thermometers (considered the gold standard method), microchips, and an IRT camera once daily for three days.

Upon reviewing the data, the team determined that the average temperature recorded with a rectal thermometer in the ponies with EHV-1 was 103.6⁰F; the average temperature with the microchip was 103.8⁰F; and the average temperature with IRT was 100.8⁰F. Though the average IRT temperature was lower than the rectal temperature, Johnson noted that the two methods' readings were positively correlated (an increase in rectal temperature corresponded to an increase in IRT temperature) and that the ponies with fevers could be detected using the IRT temperatures.

"To be a good replacement to other methods used to measure body temperature, IRT needs to be rapid, easily accepted by the animals, and strongly associated with body temperature as determined by ... rectal thermometer," Johnson said. "The results of this study support the use of IRT as an additional method, but not as a sole method, for measuring temperature."

Johnson noted that further studies are needed to determine if outside factors (such as the angle of the eye to the camera, the amount of moisture in the eye, any eye injuries or diseases, or ambient temperature extremes) could have influenced the outcome of the IRT readings.

Currently, Johnson believes that IRT's most practical use for measuring body temperature might be "as a preliminary screening tool" during a possible infectious disease outbreak: "The eye temperatures of all equids at an event are measured and those with temperatures higher than a (specific) cutoff value are selected for further evaluation." This would allow authorities to intervene quickly and attempt to halt the spread of disease.

The study, "Thermographic eye temperature as an index to body temperature in ponies," was published in the February 2011 issue of the Journal of Equine Veterinary Science. The abstract is available online.

About the Author

Erica Larson, News Editor

Erica Larson, News Editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado, and enjoys photography in her spare time.

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