Written by Jennifer F Johnson VMD, CVPP
Americans love horses. In 2017, the American Horse Council published an economic study concluding that there were over 7.2 million horses in the USA. The American Association of Equine Practitioners reports nearly 9300 members worldwide. Although pet horses remain popular, equine veterinarians are seeing more performance and sport patients, and the racing industry, while in some decline, is still a 5.3-billion-dollar market in 2020. These equine patients require consistent and proactive medical care to stay in performance shape, and this is where thermal imaging really benefits the equine veterinary practice.
Thermal imaging is not new to the equine industry. The first research regarding equine thermal imaging was published in 1972, where thermography was used to study the superficial flexor tendon (Stromberg 1972). In subsequent decades, veterinarians continued to explore thermography with variable success. Recent developments in thermal imaging have created a renewed interest, and the technology is now becoming standard-of-care among equine practitioners.
Thermography uses specialized imaging to measure the radiant energy from the surface of a patient. Differences in surface temperature patterns can suggest an underlying issue. Medical thermal imaging utilizes the natural thermal symmetry found in a living being and identifies any asymmetry as an indication of an area of concern (Soroco et al. 2017). Increases suggest inflammation, infection, or blood vessel dilation, while decreases signify vasoconstriction, nerve impingement or muscle atrophy.
Horses are prey species and are notoriously good at hiding signs of disease. Thermography provides an easy, non-invasive physiologic assessment which can pinpoint areas of concern before seeing changes on radiographs or ultrasound. Veterinarians can use thermal imaging to quickly screen the entire patient, allowing more rapid diagnosis of potential issues such as areas of musculoskeletal pain, stress fracture, or vascular disease. Because radiograph changes of osteoarthritis do not appear until much later stages of disease, thermography has been useful in providing early diagnosis (Vaden et al. 1980).
Horse racing has undergone intense scrutiny over the last few years, as the incidence of death among racing horses has increased exponentially. After Santa Anita racetrack in California was investigated for a particularly high death rate in 2018-2019, the state horse racing board performed an investigation and concluded that more stringent pre-race examinations should be instituted, with compulsory standardization nationwide. See the full report here.
Thermal imaging could provide clues to ensure that horses are ‘safe’ to race. A recent study looked at the use of thermography to monitor thoroughbred racehorses in training. Initially, all horses enrolled showed thermal balance, but as training progressed, four horses were withdrawn from the study and removed from training because of metacarpal thermal changes. The investigators concluded that the thermal images revealed changes before clinical symptoms of disease and suggested the tool is helpful when preparing horses for competition and for anticipation of injury or occurrence of lesions (Prochno et al. 2020).
Proper interpretation of thermal images is the key to success. Veterinarians trained in thermography can interpret images taken using specialized medial thermal imaging equipment. These devices have exceptional sensitivity of <0.02 degrees C and are calibrated differently than thermal cameras used in industry. Medical thermal images that reveal anatomical temperature differences of greater than 1 degree C are considered significant. Veterinary thermography can help the equine veterinarian focus on where to look. With great sensitivity, thermography will complement other anatomical diagnostic imaging tools, guiding diagnosis in a pain-free, economical, and comprehensive way.
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