Every equine veterinarian has encountered a patient whose temperament makes them weigh the risks and benefits of taking a rectal temperature as part of their complete physical exam. Digital rectal thermometers can take up to 60 seconds to report a temperature reading, exposing practitioners to the risk of a kick injury.
Noncontact infrared thermometers became common for measurement of human body temperature during the COVID-19 pandemic and may be a reasonable option in situations where obtaining a rectal temperature is deemed to be unsafe. However, the accuracy of these thermometers in comparison to digital (contact) thermometers for use in clinical settings has been questioned.
Project Design
As there is little information about the utility of infrared thermometers in horses, we designed this project to assess the repeatability of infrared thermometer temperature readings and evaluate the correlations between digital rectal temperature and infrared thermometer temperatures measured at different anatomical locations in healthy horses.
A cohort of 101 healthy horses over 1 year of age presenting to the Veterinary Teaching Hospital for elective procedures had a rectal temperature obtained, and then an infrared thermometer was used to collect temperature readings at the gingiva, eye, axilla, perineum, and neck.
Findings
Of these locations, only the eye and perineum were both repeatable and moderately positively correlated with the rectal temperature, although both were lower than the rectal temperature. Thus, an adjustment factor would be needed to use these measurements for estimation of true rectal temperature, similar to what is done in pediatric medicine when an axillary temperature is used for children who cannot yet hold a thermometer in their mouth.
Based on the data in this study, an adjustment of +2.3°F (1.23°C) for the eye and +1.4°F (0.77°C) for the perineum would be recommended to approximate rectal temperature.
Continuing Research
It is important to note that these results were obtained under climate-controlled conditions (average 72°F). When a smaller group of horses were evaluated outdoors at 20°F and 48°F, the infrared thermometer readings were highly variable at the perineum, making that a potentially less useful location for field evaluation. The eye still provided a good estimation of rectal temperature, and a larger study is under way to validate these findings under different environmental conditions.
There is also additional work to be done evaluating the utility of infrared thermometer readings in horses with fevers and in young foals. However, while the digital rectal thermometer will remain the gold standard to assess temperature in a clinical setting, noncontact infrared thermometer measurements offer a viable alternative in situations where safety is a concern.
By Chelsea Zovrist, DVM, Rebecca Bishop, DVM, MS, DACVS-LA, and Annette McCoy, DVM, MS, PhD, DACVS-LA
Editor’s note: This article was first published in J Am Vet Med Assoc 2024 Mar 8;262(6):791-797. doi: 10.2460/jav-ma.23.12.0714. Print 2024 Jun 1.
