Food and water, of course. Depending on the type of food they are being fed, some horses require a mineral supplement to maintain good health. Other horses who may have a health issue or injury require treatments, bandage changes, or hand walks daily or twice daily. And I honestly believe that in order for a horse to maintain their mental and emotional health, they need to have some form of contact (whether with a human or other horses) every day. Some horses require more stimulization than others; what I mean is that some horses have to stay busy. They do best with a job that takes up good portions of their day and keeps them thinking. Usually, these are the same horses that develop behavioral issues when kept stalled; cribbing, windsucking, weaving, pacing, pawing(digging), etc.