A mini solution
In “Help for a Lonely Mare” (Consultants, EQUUS 477) someone had a lonely mare and was having difficulty finding a suitable pasturemate. I have dealt with the same issue, with both a mare and a gelding. The solution was simple and worked equally well with both horses: My farrier suggested that a miniature donkey might do the trick. He was correct; my mini donkeys have been absolutely ideal as pasturemates. They are easy to get along with, inexpensive to keep and my horses loved them.