On average, the untreated HIV infected patient will progress to AIDS in about 5-10 years. Since 1996, the introduction of powerful anti-retroviral therapies has dramatically changed the natural progression of HIV infection to the development of AIDS.
You CAN feed your horse just hay, but you have to up the portions and it also depends upon the type of hay you are feeding. Alfalfa mix is normally the best but there again, you're goinng to have to feed more hay to make up for the not feeding grain when you are riding.
Horses under the care of humans eat a variety of diets depending on what work they do, age and health. Most horses are fed largely hay, with portions of oats given once a day. Others receive less hay and oats, but spend the day grazing grass in pastures. The mix of feed depends on how active the horse is; more work will require more calories from grains.