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.
The natural diet of the horse is grass. Grass contains most of the nutrition a horse requires to be healthy. It also contains silica, which is important for dental health. Primitive horses can live on sparse rations and often have to make do with less than ideal pasture and living conditions.