In North America and Europe, donkeys are often used as 'guard' anaimls and are expected to protect livestock from coyotes and wolves. In the Middle East, South America, Mexico, and Africa, they are often used as pack animals and forced to carry loads far exceeding their capacity.
Donkeys have varying strength in their limbs and backs, just like people. They are not designed anatomically to carry large loads. But because of their gentle nature, and their apparent sure footedness, they are often forced to work until they collapse.
The misconception that a donkey is a good 'guard' animal is based on a donkey's keen senses of sight and smell. It is also based on their ability to stand their ground when confronted by something new or dangerous. But at the same time, this misconception exploits a donkey's sense of fear. Donkeys are often loyal to their herdmates and to themselves. When a fox or coyote threatens them, they may react in fear. To take advantage of their sense of fear is exploitative and cruel. What is the solution for people who need a 'guard' animal? Improve the fence around your property. There are some great options in fencing available now.
If you see donkeys with overgrown hooves, or who have no access to shelter, hay, or water, call the local Society for the Protection of Cruelty to Animals immediately. Tell the representative about what you have seen, document the condition of the donkeys. If the donkeys seem in extreme duress, call the police. It is against the law in Ontario to withhold vet care, food, shelter, and water.