Keep electrical plugs and cords out of reach of horses. Provide a vaccination program recommended by your veterinarian. A horse's digestive system is very sensitive and reacts to any sudden change in diet. Consult your veterinarian regarding the appropriate diet for the horse's age and activity level. Always provide shelter from bad weather with a clean place to lie down.
Horses really do enjoy lying down, despite the myth that they only sleep standing up.
If you don't have a barn, a 3-sided loafing shed can suffice as protection from summer sun and flies and winter wind and storms. This means scrubbing tubs and buckets regularly. Groom horse often to remove dirt and stimulate the skin and coat. Horses are happier if they have company. If you own only one horse, perhaps a neighbor's horse can suffice, or a miniature donkey, goat, or even a chicken can be a barnyard companion.