A new blood analysis failed to reliably distinguish horses with gastric ulcers from those without the disease, in a study that highlights the difficulties in assessing pain in these animals. The investigation was conducted by veterinarians from the University of Adelaide, in Australia, and published in The Veterinary Journal.
Gastric ulcers affect a substantial proportion of horses, especially in the context of racing, but researchers still cannot reliably determine which animals feel pain or the clinical relevance of the lesions found.
The study sought to assess whether certain immune system cells present in the blood could provide a measurable signal of the equine gastric ulcer syndrome.
To this end, the researchers collected blood samples from 77 horses and exposed immune cells to substances intended to trigger an immune response. Subsequently, they measured the production of a molecule called interleukin-1 beta (IL-1β), associated with pain and inflammation in other species.
However, the method did not reliably distinguish horses with gastric ulcers from those without the disease.
Of the 64 animals included in the final analysis, 59, or 92.2%, had gastric lesions. Only 25% of the horses showed a measurable response in the blood cell test. No significant association was found between this response and the presence of equine gastric ulcer syndrome.
The researchers also did not identify significant differences in facial pain scores between horses that responded to the test and those that did not respond.
“Horses cannot tell us when they are in pain, and signs of discomfort can be subtle, inconsistent, or easily overlooked,” says Gustavo Ferlini Agne, from the School of Animal and Veterinary Sciences at the University of Adelaide.
The researcher emphasizes that objective ways are needed to identify when a horse is suffering, especially in the case of gastric diseases, where the existence of a lesion does not necessarily determine the degree of pain or discomfort felt by the animal.
“Our study shows that this specific blood test is not yet the solution, but it also provides important information on where we should look next,” he adds.
Equine gastric ulcer syndrome is particularly difficult to evaluate because horses may present few outward signs. Moreover, behavioral indicators of discomfort are not always consistent.
The disease has a high prevalence, especially among Thoroughbred horses used in racing. Earlier studies identified gastric disease in 80% to 100% of racehorses for one of the main forms of the disease.
According to Ferlini Agne, identifying clinically relevant pain “could have major implications for the welfare of horses, enabling veterinarians and owners to make more informed decisions about treatment and management” of the animals.
However, the researchers caution that the results do not mean that gastric ulcers do not cause pain. They suggest instead that the immune response measured in circulating blood cells may not be sufficiently sensitive to detect the effects of the ulcers, especially when inflammation or pain are localized in the stomach.
Larger-scale studies and diagnostic methods specifically tailored to horses will be needed. The team also advocates for an approach that combines biological indicators with a careful assessment of pain-associated behavior and inflammation.
“This is an important step, because knowing what doesn’t work is as valuable as identifying a promising test,” says Ferlini Agne.
The ultimate goal, he adds, is to provide veterinarians with better evidence to recognize and treat potentially painful situations, rather than relying solely on the indirect assessment of signals presented by the animals.
