Infrared thermography put to test for assessing equine temperature

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Researchers find that maximal eye temperature differs between breeds and sexes but not with age and size.
Photo by Anna Jannson et al (CC by 4.0)

Measuring equine eye temperature by Infra-Red thermography (IRT) is a popular technique as it is non-invasive and does not require direct contact with the individual, but it does not appear to be sensitive enough to monitor fever in the horse, a recent study has found.

In horses, Maximal eye temperature (MaxET) has been applied to detect body temperature/fever, stress from competitions, the fit of different bridles, aversive management (e.g. clipping), fear, housing system, physical exercise/fitness and poor performance.

The method has been extensively used in equine research, but fresh research indicates it is affected by endogenous (sex and breed) and environmental factors and shows no relationship to rectal temperature.

A study, by Anna Jannson and colleagues, published in the journal Physiology and Behavior, investigated factors influencing eye temperature in horses when measured using infra-red thermography (IRT) under field conditions.

The research team took 791 maximal eye temperatures (MaxET) measurements from 32 horses in Sweden in five different months and on five farms over a 12-month period.

They found that in horses observed at rest in their home environment, MaxET is affected by endogenous and environmental factors (farm, location, and month of the year).

The authors point out that these findings have relevance in both clinical and research settings.

“This indicates that eye temperature does not appear to be a sensitive method to monitor for example fever, where rectal temperature is traditionally used.”

They found no linear correlation between IR eye temperature and rectal temperature (measured using conduction) but said that this was “not surprising since the accuracy of the IR camera, according to the manufacturer, is 2 °C. However, it is also possible that a non-linear behaviour between eye temperature and rectal temperature exists”.

They add “endogenous (sex and breed) and environmental variation between months were major factors influencing eye temperature and should be considered in the modelling and design of future field experiments”.

The work was carried out by Jansson, who is with the Swedish Department of Anatomy, Physiology and Biochemistry in Uppsala; Gabriella Lindgren, from the Department of Animal Breeding and Genetics at the Swedish University of Agricultural Sciences; Brandon Velie, from the School of Life and Environmental Sciences at the University of Sydney in Australia; and Marina Solé, from the Department of Biosystems Faculty of Bioscience Engineering at the Katholieke Universiteit Leuven in Belgium.

The work was supported by the Swedish Research Council for Sustainable Development – FORMAS (Research and development projects for future research leaders).

An investigation into factors influencing basal eye temperature in the domestic horse (Equus caballus) when measured using infrared thermography in field conditions. Anna Jansson, Gabriella Lindgren , Brandon D Velie , Marina Solé. Physiol Behav (2021); 228:113218. doi: 10.1016/j.physbeh.2020.113218.

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