New study highlights difficulty of detecting gastric ulcer pain in horses

A new study led by Australian veterinarians has exposed the challenge of identifying pain in horses with gastric ulcers and highlights an urgent need to better detect when horses are suffering.

Gastric ulcers affect a large proportion of horses – particularly racehorses – but scientists still cannot reliably tell which animals are experiencing pain or how clinically significant the ulcers are.

Now, Adelaide University researchers have tested a potential new blood-based method for detecting the biological changes associated with gastric ulcers.

The study, published in The Veterinary Journal, investigated whether immune cells taken from a horse's blood could provide a measurable signal of Equine Gastric Ulcer Syndrome (EGUS).

Researchers collected blood from 77 horses and exposed immune cells from the blood to substances designed to trigger an immune response. They then measured production of a molecule called interleukin-1 beta (IL-1β), which has been linked to pain and inflammation in other species.

However, the test failed to reliably distinguish horses with gastric ulcers from those without them.

Dr Gustavo Ferlini Agne, from Adelaide University's School of Animal and Veterinary Sciences, said the result highlights just how difficult it can be to identify pain in an animal that cannot tell us where it hurts.

Horses can't tell us when they are in pain, and signs of discomfort can be subtle, inconsistent or easily overlooked.

We need objective ways of identifying when a horse is suffering, particularly with gastric disease where the presence of a lesion does not necessarily tell us how much pain or discomfort an individual horse is experiencing.

Our study shows that this particular blood test is not yet the solution, but it also gives us important information about where we need to look next."

Dr. Gustavo Ferlini Agne, Adelaide University's School of Animal and Veterinary Sciences

Of the 64 horses included in the final analysis, 59 – or 92.2% – had gastric lesions.

The researchers found that only 25% of horses showed a measurable response in the blood-cell test. There was no significant association between that response and the presence of EGUS, and the test could not reliably distinguish horses with or without the disease.

The researchers also found no significant difference in facial pain scores between horses that responded to the test and those that did not.

EGUS is particularly difficult to assess because horses may show few obvious outward signs, while behavioral indicators of discomfort are not always consistent.

The condition is highly prevalent, particularly in the Thoroughbred racing industry, with previous studies reporting gastric disease in 80–100% of racehorses for one major form of the disease.

"Being able to identify clinically important pain could have major implications for horse welfare, allowing veterinarians and owners to make better-informed decisions about treatment and management, Dr Ferlini Agne said."

The researchers stress that the findings should not be interpreted as evidence that gastric ulcers do not cause pain.

Instead, the results suggest that the immune response measured in circulating blood cells may not be sensitive enough to detect the effects of gastric ulcers – particularly if inflammation or pain is localised to the stomach.

Dr Ferlini Agne said larger studies and horse-specific testing methods will be needed.

"This is an important step because knowing what doesn't work is just as valuable as identifying a promising test.

"The next challenge is to develop approaches that are better suited to horses and combine biological measures with careful assessment of pain-related behavior and inflammation.

"Ultimately, the goal is to give veterinarians better evidence to recognize and manage presumptively painful conditions, rather than relying on guesswork."