Thank you, TWH, and Jill; this is so strange, but when the vet looked at the horses teeth, he said he's a lot older than she thought; he could be around 30 yrs old. I'm not sure how long she has had him, but she had him shipped here from CA. early this Spring. He was her buddy for many years, apparently.
DH had stopped in there briefly today and the vet was there, and he mentioned that he had to put him to sleep; I know he hadn't been eating for a while, and she was giving him some supplements and bought alfalfa hay for him, also, but he wasn't improving...his ribs were showing.
It sounds silly, but could he have been jealous of her other two horses, and could that have made or helped him to deteriorate like that??
When I get a chance, I'll ask just what might have been wrong; but won't ask her tomorrow unless she brings it up. I know she's still upset, as I would be for a long time, I'm sure.