Mules endure heat better than horses do. It has been scientifically proven that the donkey is similar to the camel in its ability, when water starved, to drink only enough water to replace lost body fluids. Most mules inherit this ability. Water founder in a mule is so rare as to be notable when it does occur.
Mules have fewer feeding problems than horses do.
Many farmers keep their draft and work mules together in pens with feed available at all times, yet the mules rarely overeat to the point of colic or founder. Mules from pony mares, however, may grass or grain or road founder, so the idea that a mule never founders is not true. People who buy cheaper weedy hay find that their mules clean out the weeds first. Mules eat less than horses do. Mules that are not working usually don't need grain at all.