There are almost 52,000 donkeys in the United States, including domesticated and wild animals. Experts estimate the world’s donkey population to be 40-50 million.1 A recent study2 published about free-roaming donkeys in the U.S. provides insights on their domesticated relatives.

Study: Free-Roaming Donkeys in Southern California

Feral donkeys (Equus asinus) are well adapted to arid ecosystems. The deserts of Australia and the Americas have large donkey populations.

This study looked at donkeys in the Mojave Desert in Southern California, including the contiguous area of Fort Irwin National Training Center and Death Valley National Park. Donkeys were trapped in pens using alfalfa hay as bait. Then, researchers performed health assessments and placed GPS trackers. The trackers had timed remote release mechanisms set to drop off after 130 weeks of deployment.

The study included 21 female and 11 male donkeys. The researchers did not use the male statistics because of insufficient data due to lost or damaged tracking collars.

All donkeys were assessed for:

  • nasal discharge (presence/absence),
  • cough (presence/absence),
  • ocular discharge (presence/absence),
  • skin lesions (absent, swelling, hair loss, minor wound, deep wound),
  • lameness (not lame, lame, not moving),
  • and behavioral presentation (aggressive, alert, fearful, withdrawn, apathetic, lethargic).

Researchers collected nasal swabs to test for disease while restraining the donkeys for collar fitting.

Diseases Prominent in Wild Donkeys

Both Streptococcus equi zooepidemicus (SEZ) and asinine herpesvirus 5 (AHV-5) detected in feral donkeys in Death Valley are highly infectious among equids.

“Donkeys can act as disease reservoirs,” noted the researchers. “While they might be susceptible to diseases from horses, they can also transmit them. AHV-5 has the potential to co-infect horses, presenting as equine multinodular pulmonary fibrosis.”

SEZ has the potential to affect all equids but can also affect other livestock, carnivores, and humans, causing bacteremia, meningitis, and arthritis in people, they noted. Donkeys might not demonstrate clinical signs of disease, so owners and managers should implement biosecurity measures—such as disinfecting equipment—when handling or transporting these animals from a feral to a domestic setting.

The researchers noted that infection with AHV-5 and/or SEV was inapparent when donkeys were closely observed. They said all animals appeared alert and in good condition.

Twenty-one individuals had bacterial presence of SEZ, and 11 had viral presence of AHV-5, with eight individuals testing positive for both. All other disease assays were negative. “There were no known mortalities during this study,” the researchers said.

Social Systems for Feral Donkeys

“In arid environments, donkeys have a fission–fusion social system,” explained the researchers. “In these social systems, there are no permanent social associations between adults, but individuals come together and separate as they independently forage.

“However, the social network of donkeys is saturated, as individuals are well connected with many other individuals in the population,” they explained. “Where individuals have a high number of social partners that interact with other social partners, as observed in a Sonoran Desert feral donkey population, there is an increased probability of disease spread among a population.”

Climate, Disease, and Movement

“Our results indicate that lower heat loads are relatively more important than green vegetation production for predicting space use of donkeys during the hot/dry season in Death Valley,” noted the researchers.

However, they found movement differences in donkeys that had SEZ or AHV-5.

“Donkeys with evidence of SEZ selected lower elevations relative to non-infected conspecifics [other donkeys in the study] in the wet season and closer proximity to water in the dry season,” stated the researchers. “Comparatively, donkeys with evidence of AHV-5 selected more rugged terrain in the dry season and farther distances to water during the wet season.”

Some strains of herpes virus (such as EHV-1 and -4) can be spread through aerosol transmission from nasal discharge. Infectious discharge from an infected animal can remain infectious on fomites (objects such as wood and straw) for up to seven days.

SEZ is transmitted through close contact between individuals, noted the researchers. While less congregation of donkeys is expected near water sources in the wet season, “use of these areas could promote transmission among the population,” the researchers noted.

Final Words

“Despite donkeys being arid-adapted, we showed that their movements, ranges, and habitat use were shaped by precipitation and the presence of water,” noted the researchers. “Our results imply that while there is the potential for disease to spread among the population based on donkey social structure, this is mediated by low prevalence of the disease and different habitat use by infected animals.”

References

  1. Donkey Population by Country 2026. World Population Review
  2. Movement Ecology and Disease Exposure in Free-Roaming Donkeys in California, USA. Sarah R. B. King, Amy McLean, Jacob D. Hennig, and Kathryn A. Schoenecker. Animals. 2026

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  • Kimberly S. Brown and Jewell

    Kimberly S. Brown is an award-winning writer and publisher. She founded My Senior Horse for Equine Network and Linda Mars in her retirement, and now she is an editor of the brand. Brown previously had spent 10 years at Equine Network. Prior to that she worked for three years in equine nutrition after she retired from nearly 30 years working at The Blood-Horse. Brown spent the last 15 years of her time at that organization creating and developing the award-winning The Horse and TheHorse.com.

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