TheIT said:
How do horses establish their pecking order? What about horses interacting with mules?
It's very complex. Not only do horses have individual status (lead mare is lead mare because she knows the best grazing sites and when to move where for water; lead mare's foals are likely to grow up having higher status than foals of subordinate mares; and so on), they have status related to certain activities (Horse A drinks first, but Horse B eats first, and Horse C gets the best place to sleep) and status related to who their pair bond is (Horse A is best buddies with Horse D, so even though Horse D is dominant to no one, he probably doesn't get picked on much). Pecking order is often established through biting, shoving, and kicking, or threatening to bite or kick, and reinforced by the dominate horse proving it can place the subordinate's body anywhere it wants to relative to the dominant's.
In my WIP, one of the main characters has a mule. She gets a visitor who then stables his horse with the mule. Would the mule defer to the horse? Would they need to be separated?
Whichever is dominant will depend on the personalites of each. My 7-year-old, 16-hand horse was bullied unmercifully by a 3-year-old, 13.3-hand pony. Any equines you put together are going to have an adjustment period when they work out who's in charge. Keeping them physically separated (like with a fence, or in separate stalls, where they can still interact) while they get to know each other lessens the chances that one of them will end up injured when they finally do get together.
How much space do you need to keep a horse/mule? Would it have problems being stabled in a cave (at least part of the time)?
Keep them, how? Keep them stabled? Modern stalls are usually 12 feet by 12 feet, with 10 feet by 10 feet considered the minimum. This size lets the horse move around and lie down (horses can doze standing up, but can only sleep lying down; a too-small stall can result in a horse getting "cast," or unable to get back up). For a long time, especially in Britain, stalls were barely bigger than the horse, and horses were tied when standing in them. How the poor things slept, I don't know.
As for caves, horses have Issues-with-a-capital-I about enclosed, dark places. Getting them to load into horse trailers can be a real adventure. Getting them to walk into a dark cave which probably smells like lots of predators (because good caves don't go unused)...um. I don't know. If the horse was very easygoing and trusted you, maybe. Keeping it in a cave is going to bring up other problems, too, like waste disposal (horses drink gallons of water per day, which is going to become urine in due time, and they eat lots and lots of roughage, which becomes bulky manure) and carrying food and water to it. Nor is air circulation the greatest, which leads to respiratory problems. And if the floor is uneven, not only would that make cleanup harder, but you'd stand a good chance of their bruising the soles of their feet, and you really don't want to have to deal with abscesses and the like.
Have I mentioned that many things can go wrong with horses? Many, many, many. Feet and digestion are often the biggies. Horses can die of colic, they can founder, they get splints and ringbone and azoturia and chronic obstructive pulmonary disease and I have to stop before I cry.