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 can do well on grass or alfalfa (or other legume) hay. Important factors to keep in mind for horse hay are the nutritional needs of the animals (mature horses will not need high protein or calcium levels unless they are mares nursing foals), and the way the hay was harvested.