Donkey standing in pasture

Donkeys don’t neigh; they bray. They prefer to live in pairs instead of large herds. And now, researchers have found another major difference between horses and their long-eared cousins: They have dramatically different laminitis risks.

According to recent study results, donkeys—unlike horses—that are more prone to the hoof disease laminitis are younger than those that aren’t, do not necessarily receive extra concentrated feeds, and don’t always have other health problems, said Nicola Menzies-Gow, MA VetMB, PhD, DipECEIM, CertEM(IntMed), FHEA, MRCVS, Dipl. ECEIM, lecturer in equine medicine at the Royal Veterinary College, in Hatfield, the U.K.

This runs counter to standard risk factors for ponies and horses (Equus caballus). In horses and ponies, laminitis is most likely to strike animals that are overweight, receive too many high-starch concentrates, or are undergoing certain medical treatments or dealing with lameness. This study highlights the importance of recognizing donkeys (Equus asinus) as a unique equid species with its own host of risk factors, said Menzies-Gow.

“Unfortunately for a lot of conditions, including laminitis, it is assumed that donkeys are just small horses or ponies,” she said.

Laminitic Donkey and Horse Records Compared

Menzies-Gow and her fellow researchers investigated 42 months of records for 707 donkeys living at the Donkey Sanctuary, which cares for 35% of all donkeys in the U.K. on 11 sites across the southwestern U.K. In that time nearly 50% of the study donkeys experienced at least one episode of laminitis—compared to up to 34% found in studies involving horses and ponies, she said.

A little more than 40% of those donkeys had at least one recurring episode of laminitis in that same time frame—similar to recurrence rates in horses, Menzies-Gow said. Overall, 65% of the donkeys with laminitis had chronic, rather than acute, disease. About 9% died as a result of laminitis during the study period.

The donkeys that had their first episode of laminitis in this study were younger than those that did not, Menzies-Gow said. While the study population was relatively old—given that it was a refuge—the age results were nonetheless significant, she explained. The donkeys experiencing laminitis—averaging 19 years old in this study—were older than the average age of horses and ponies experiencing laminitis—on average 14.8 years in earlier studies.

Furthermore, and contrary to findings in horses, donkeys experiencing acute laminitis were “significantly less likely to get too much feed in comparison to their nutritional needs, to have another medical condition, or to have undergone dental work, movement, or diagnostic imaging in the month preceding the laminitic episode compared with the control group,” Menzies-Gow and her fellow researchers reported.

Donkey Management Considerations in the Study

“It is not surprising that donkeys are different compared to horses and ponies,” Menzies-Gow told The Horse. “Evolutionarily, they were designed to live in very different environmental conditions to those that they are kept in the Western world. Food is abundant, and they undertake minimal physical exercise.

“Prior to undertaking the study, I thought the laminitis risk might be related to insulin dysregulation; however, it was not significant when the statistical analysis was undertaken,” Menzies-Gow continued. “However, it must be remembered that dynamic testing for insulin dysregulation was not performed in any of the donkeys, and basal insulin concentrations were not measured in all animals, so further studies are warranted.”

As for the effect of pituitary pars intermedia dysfunction (PPID, aka Cushing’s disease), 20% of the study donkeys and 22% of the laminitic study donkeys had PPID based on basal adrenocorticotropic hormone (ACTH) concentrations, Menzies-Gow said.

While horses usually experience laminitis in spring or late summer, when grass has the richest sugar content, the researchers saw the most laminitis cases in donkeys in January, February, October, and November, Menzies-Gow said. Because that corresponds to the period when many donkeys come into the stables off pasture for the winter, the episodes might be related to dietary and management changes, including spending more time standing on concrete, she said. Lameness related to laminitis might simply have been easier to detect once the donkeys were walking on concrete, Menzies-Gow added.

Furthermore, because the donkeys were generally dewormed in January, she hypothesized a potential link between the gut microbiota changes related to anthelmintics and the development of laminitis in donkeys—a theory she said deserves more in-depth research.

Since donkeys tend to be more stoic in reaction to pain, it’s possible that the experienced veterinarians managing these study donkeys missed some laminitis cases, said Menzies-Gow.

“The Donkey Sanctuary works hard to keep all the donkeys under their care at an optimal body condition and uses all available methods to prevent laminitis,” she said. “However, laminitis can affect any donkey, horse, or pony, even if everything is done right to try and prevent it.”

The study appeared in the Equine Veterinary Journal, online ahead of print, in September 2021.