Infrared thermography is a non-invasive technique used to quantify body temperature of various tissues. Thermography has many applications in equine medicine. A unique one is that of measuring the maximum eye surface temperature. A Brazilian study set out to use eye surface temperature as a parameter for defining physical fitness of ranch horses [Trindade, P.H.E.; Ferraz, G.C.; Lima, M.L.P.; et al. Eye surface temperature as a potential indicator of physical fitness in ranch horses. Journal of Equine Veterinary Science Nov 2018].
The physical fitness of 16 horses working on a beef cattle ranch was evaluated through specific biomarkers: eye surface temperature maximum (EST), respiratory rate, creatine kinase (CK), total protein, plasma cortisol and lactate. Also assessed were each horse’s heart rate during exercise, the duration of the exercise, the average speed, distance, and ambient temperature and humidity. Ten of the study horses worked half a day; six worked both morning and afternoon with an hour or so break for lunch. The predominant proportion of work was done aerobically at low speeds. Daytime temperatures were high during the summer months of the study. Thermography was performed on the eyes with the horses in the shade in order to eliminate solar radiation effects on eye temperature.
Analysis of the results demonstrated that there was no difference in EST between dehydrated and non-dehydrated horses. What was observed is that there was a difference in EST for horses having high (> 350 U/L) or low CK values. Creatine kinase elevations in serum generally correlate with muscle damage following exercise.
It is thought that an increase in eye surface temperature is associated with vasodilation of the ocular tissues in response to increased body heat. Based on the study results, the correlation of EST with CK might yield information about muscle fatigue. The authors suggest that this could help determine the interval of rest to allow muscle recovery following exercise activity.
A Smartphone app that captures thermograms might be a helpful and affordable tool in future to determine physical fitness in equine athletes and to help manage appropriate recovery time to avoid further muscle damage. More studies are needed for corroboration of these findings and to prove thermography's effectiveness.