Donkeys are more likely to enjoy the heat and sun of summer than horses, according to researchers.
However, when winter bites, horse are better suited to the colder conditions.
New research from the University of Portsmouth shows that donkeys are keener on hotter periods of the year, preferring sun and warmth.
The research, published in the Journal of Applied Animal Behaviour Science, is the first to examine the conditions under which healthy non-working donkeys and mules seek shelter in hot, dry climates.
The research by the university’s equine behaviour expert, Dr Leanne Proops, found that while mules would prefer to seek shelter from heat and insects, donkeys enjoyed the sunshine and warmth for longer.
“We found that donkeys are less likely to seek shelter from the heat and light than mules. The sensitivity of mules to higher temperatures and sunlight may be due to the geographically different evolution of horses and donkeys and their adaptations to different climates.
“Donkeys are better adapted to arid, hot climates and hence higher sunlight levels.
“In contrast, horses are more adapted to cold conditions, and our previous research has shown that donkeys seek shelter far more often than horses in cold, wet conditions.
“As a hybrid, mules often display attributes that are a mixture of both species, such as their winter hair coat growth. Therefore, it might be expected that mules are less adapted to conditions of high temperatures and sunlight levels than donkeys, as we found in this study.”
It is known that the effect of heat in the environment becomes physically challenging for animals once the ambient temperature surpasses their thermal neutral zone (TNZ).
The TNZ is different for every species. An important method of controlling heat stress from solar radiation is for an animal to seek shade.
For the research, a total of 130 donkeys and mules were studied in two locations in southern Spain in a seven-week period during the summer. In both locations, researchers recorded the animals’ need for shade.
All the animals in the study were healthy, had free access to shelter and were regularly monitored by vets from British charity The Donkey Sanctuary.
Temperatures during the study period ranged from 14 to 37 degrees Celsius and information was collected between 8am and 4.15pm. For each location outside temperature, wind speed, light levels, rainfall, insect density and harassment levels were recorded.
Emily Haddy, a PhD student who worked on the project, said: “It has been very interesting to see the results from this study. Despite what equid owners may think, it is clear that different equid species have specific needs and so should be given free access to shelter — there is no ‘one size fits all’.”
Dr Faith Burden, the director of research and operational support at The Donkey Sanctuary, and co-author on the paper, points out the importance of these findings.
“The majority of working equids worldwide are exposed to hot climates and as a consequence may suffer from issues such as dehydration and heat stress.
“By establishing the natural shelter-seeking behaviour of healthy donkeys and mules across climates we hope to be able to inform welfare guidelines and encourage good management of these animals.”
Anyone with domestic donkeys facing the bite of a northern hemisphere winter is urged to keep them warm and dry.
Donkeys found to struggle in cold winters
In earlier research published in 2017, it was found that donkeys are not as able to keep as warm as horses in Britain’s cold, damp winters.
The study, by scientists at the Universities of Portsmouth and Canterbury Christ Church University, recommended that the animals be given extra winter protection.
Proops, who was one of the authors of the study, published in the Equine Veterinary Journal, said: “The common perception is donkeys are hardy and capable of enduring challenging environments.
“While it’s true they’re highly adapted to the harsh, semi-arid environments, it would be wrong to assume this hardiness allows them to thrive under all conditions.
“Our results showed that unlike horses, donkeys are not able to adjust their hair coat weight, hair length and width in response to colder, winter weather, which suggests donkeys need welfare guidelines separate to those for horses.
“We’d suggest they need man-made protection from wind and rain.”
The researchers also found the intermediate nature of mule hair coat properties should also be considered.
The research examined the insulation properties of the hair samples (weight, length and thickness) which showed that donkeys’ coats do not change significantly across the seasons and that their coats were significantly lighter, shorter and thinner than that of horses and mules in winter.
In contrast, the coats of horses and ponies changed significantly between seasons, growing much thicker in winter.
Dr Burden, from The Donkey Sanctuary, said: “For many years it has been the ‘common sense’ advice given by The Donkey Sanctuary to ensure that donkeys and mules are given the right protection from our cold winters.”
The 2017 study provided the scientific evidence to show why the welfare needs of donkeys and mules differ slightly to those of horses and ponies, and how owners can act to give them better protection from the elements, she said.
When do donkeys seek shelter?
So, what sort of conditions might see donkeys opting for shelter?
That was answered in research published earlier this year in the Journal of Veterinary Behavior.
It was found that most donkeys seek shelter when it starts to rain and when temperatures drop below 14 degrees.
In contrast, across all weather conditions observed, most horses can be found outside.
Proops, who was involved in the research, said donkeys were much more likely than horses to seek shelter when it was windy, rainy or cold.
“This makes a lot of sense when you consider the evolutionary history of each species – horses are thought to have been domesticated in the temperate regions of Eurasia, while domestic donkeys originated from the African wild ass in semi-arid regions of Northeast Africa.
“This means that horses tend to be better adapted to the temperate climate of the United Kingdom, whereas donkeys are better suited to hotter, drier climates.
“We hope these findings can be used by those who care for either species to better protect them from conditions they’re not suited to.”
For that study, researchers studied 208 healthy, semi-free ranging donkeys and horses in Somerset and Devon over 16 months.
The temperature, wind speed, rainfall, light and density of and degree of harassment by flying insects at each site were measured to assess which factors prompted the animals to seek shelter.
All the donkeys and 30 of the 73 horses and ponies were owned by The Donkey Sanctuary, which funded the research. None of the animals were clipped or wore rugs and they had a mixture of coat colours, from light to dark.
In the data collected, the temperature varied from 1 to 33 degrees Celsius.
Overall, unless it was hot and dry, donkeys spent a great deal less time outdoors than horses, preferring the sanctuary of a shelter. When it rained, donkeys were three times more likely than horses to stay indoors.
The two species reacted very differently to wind, too, with a fresh to moderate breeze sending 61 percent of donkeys and only 5 percent of horses inside.
On bright days, donkeys were most often outside, while in the same light conditions, horses preferred to seek the shade of trees or man-made shelter.
Some significant differences in behaviour were seen in different combinations of weather conditions, too, with rain and wind together being the most likely combination to drive both species inside.
When insect harassment rose, horses went inside, and donkeys went outside, though that could be due to insect harassment increasing at higher temperatures.
Burden said it was interesting to see such a disparity in shelter-seeking behaviour between the two species.
She said it validated the sanctuary’s long-held belief that donkeys need shelter from inclement weather.
“What we didn’t necessarily anticipate finding was the horses’ preference to be sheltered from insects in the sunny summer months … it is clear that each species requires shelter at different times and for different reasons.
“We would encourage all equine owners to consider providing appropriate shelter to their animals throughout the year so that they can choose when they use it giving them the ability to manage their own needs.”
The study’s partners included Canterbury Christ Church University, the Dartmoor Pony Heritage Trust and Natural Horse Management expert Lucinda McAlpine.