The eyes of horses are a window to their soul – and their physiological status

Researchers in Italy find a correlation between rising body temperature and decreasing eye pressure in showjumping horses.
Photo by Myprofe

Exercise in horses induces both an increase in eye temperature and a drop in pressure within the eye, researchers in Italy have found.

The University of Messina study team, writing in the journal Animals, suggest eye temperature could be a good replacement for other methods to monitor body temperature where the recording of rectal temperature is not possible.

It would be interesting, they said, to consider both pressure within the eye and eye temperature as ways to determine, in a simple and noninvasive way, the physiologic status of horses during physical exercise.

Francesca Aragona and her fellow researchers said physical exercise is a natural stressor that produces a series of biological responses affecting a horses’ thermal welfare and metabolic balance.

During physical exercise, a horse’s metabolic rate increases to transport oxygen, water electrolytes, nutrients and hormones to the contracting muscles. Blood pressure rises, the heart rate increases, and thermoregulatory mechanisms kick in to dissipate excess heat.

Too much heat induced by physical exercise may be hazardous to health and physical performance.

The researchers said eye temperature, which is easily measurable using infrared technology, is used as a physiological parameter as it may reflect body temperature changes in response to events and stimuli.

“As it reflects body temperature, the measurement of ocular temperature can be used to monitor acute and chronic stress levels in horses during physical exercise and competition,” they said.

Intraocular pressure – pressure within the eye – is a fundamental parameter of eye health and disease and it is part of routine investigations in eye examinations.

It is used to ensure the diagnosis and management of glaucoma in humans and domestic animals when pressures appear, whereas lower values point to anterior uveitis and the post-operative management of corneal, lenticular and vitreoretinal diseases.

In their study, the researchers investigated changes in eye temperature and pressure in response to physical exercise in showjumping horses participating in morning and afternoon sessions, and any correlation with rectal temperature.

Fourteen Italian Saddle Horses, with an average body weight of about 520kg, were enrolled in the experiment. Each underwent a complete clinical check and eye exam beforehand, with blood chemistry also analysed.

The morning and afternoon workouts at the training center involved a specific hour-long protocol, with a warm-up and warm-down. Air temperatures during the workouts were mild.

The study team found that eye and rectal temperature increased after exercise as a result of muscle metabolism activation, increasing blood flow in several regions of the body to improve oxygen supply and heat dissipation.

Pressure within the eye significantly decreased after exercise, probably due to dilation of surrounding blood vessels arising from the workout.

The results, they said, showed a correlation between increased body temperatures and eye pressure variations during exercise, so they can probably be considered indicators of athletic horses’ physical fitness during exercise.

There was also a significant correlation between eye temperature and rectal temperature.

“Both core and surface temperature of the body can reveal how animals cope with the surrounding environmental changes,” the researchers said.

“Our findings suggest that ocular temperature may be considered as an alternative tool for non-invasive central temperature measurement as an indicator of horses’ physical fitness after a day of work.

“The superficial areas of the eye are rich in capillary beds, innervated by the sympathetic system, thus representing an ideal place to measure local changes in blood flow as a consequence of the activation of the autonomic nervous system.”

The use of a thermo-camera allows for the rapid recording of the eye temperature, compared to the digital thermometer used for measurements of rectal temperature, they said. “The results of this study support the use of infrared technology as an additional, rapid and non-invasive method for measuring body temperature.”

The study team proposed further studies in order to standardize the workload and the different physical effort intensities that may affect horses’ physical fitness after exercise and athletic horses’ welfare during competitions.

The full University of Messina study team comprised Aragona, Simona Di Pietro, Francesca Arfuso, Francesco Fazio, Giuseppe Piccione, Elisabetta Giudice and Claudia Giannetto.

Aragona, F.; Di Pietro, S.; Arfuso, F.; Fazio, F.; Piccione, G.; Giudice, E.; Giannetto, C. Correlation between Ocular and Rectal Temperature with Intra Ocular Pressure in Horse during Exercise. Animals 2022, 12, 1850.

The study, published under a Creative Commons License, can be read here

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