Can equine eyeballs reveal stress levels — and do semi-feral ponies suffer from gastric ulcers? Peter Green MRCVS explains all in his research round-up

The eyes have it

Stress response is a normal, healthy process involved in the switch from “resting and digesting” to “up and ready for action”.

Scientists have demonstrated that in a number of species, including horses, the temperature of the eyeballs correlates with the level of stress the animal is experiencing.

Research has proven that the stress levels of showjumpers can be measured by this method. Without touching the horse or taking any samples, scientists can assess stress by pointing a sensitive thermography camera at the eye. The temperature of the eyeball goes up when a horse is stressed.

Spanish scientists have just published work on dressage horses. They measured eyeball temperatures during dressage competitions in 343 stallions aged between four and six. They then compared these temperatures with the dressage scores and analysed the breeding of each stallion.

The first part of the study was as expected: for individual horses, eyeball temperature went up during the test and came down again afterwards. This confirmed that dressage tests are stressful.

But when they compared achievement with stress levels they found that the stallions who appeared more stressed were the ones more likely to score highly. This seems to show that youngsters with an enhanced stress response make better dressage horses — they are literally more “on their toes” when they need to be.

Finally, the scientists showed that there were strong indications that both eyeball temperature and stress in response to performance were highly heritable. This suggests that young potential dressage horses might be screened for future achievement by measuring the rise in the temperature of their eyeballs when they are in training as juveniles.

New findings on ulcers

Gastric ulcers are a well-recognised problem in domesticated horses.

Glandular ulcers affect the bottom part of the stomach submerged below the acid gastric juices, while squamous ulcers occur higher up where acid sloshes up only during exercise and immediately after eating.

Current wisdom is that ulcers are caused by stress, exercise and relatively unnatural intensive feeding for performance.

So we would predict that semi-feral Exmoor and Dartmoor ponies, animals that live a life just about as close to that of a wild horse as possible, would not be bothered by gastric ulcers. After all, they simply eat, breed and mooch about like the wild horse before domestication.

A recent study had surprising results. Scientists carried out postmortem examinations of the stomachs of 60 horses that had been kept in fully domesticated conditions, and 29 feral ponies from the moors. The samples were all taken from animals slaughtered in mid-summer, when grazing was at its best and the predicted environmental stress at its lowest.

When the stomachs were examined, both kinds of ulcer were found in more than 60% of fully domesticated horses — a higher figure than expected. Even more unexpected was the finding that one or other kind of ulcer occurred in more than 20% of the wild ponies.

There are several possible explanations for this. Perhaps ulcers can form really quickly and the moorland ponies developed them between round-up and slaughter. Or maybe they are not living such an idyllic, stress-free, wild lifestyle after all.

It could be that gastric ulcers are a product of domestication, reflecting the fact that moorland ponies are domesticated ponies that have become feral — rather than truly wild equids such as zebras.

Ref: Horse & Hound; 21 January 2016