This is a great topic for new horse owners and younger horse owners who are not under a parents guidance. Thank you mred for starting this.
Due to the nature of my work I had my first will in place when I was 21. I always rode whatever was available at my parents place as it was free (of course my parents still got manual labor out of me) and my parents always had nice horses that I couldn't afford and there were plenty there that needed to be ridden. As I became financially stable I bought my first horse I edited my will to include my horse. Now that I have 4 horses and am married the will has been changed many times, oh and add home ownership and a kid and..blah, blah, blah.
If something happens to me the hubby is stuck with it all, but he already claims two of the horses and I know he would never get rid of them. If something happened to both of us everything including my kid goes to my parents. If my parents are gone it falls to my brother, then aunt/uncle. I have a life insurance policy as well to cover the expense of everything.
Something younger folks don't think about is the expense of funerals, medical care, transporting, feeding until things are settled. Get a life insurance policy and state in the will that the beneficiary of the will needs to use the money to settle the expenses of said funeral/horse care/transports. A lot of youngsters can get a life insurance policy for less than 20 bucks a month and it would ease the burden on your loved ones.