Our local group doesn't own any horses, but leases horses horse owners provide for them and boards them in a local riding center with a suitable indoor for their work.
We had two to three horses always ready for their program.
They took one for two or three months, then would bring that one back and take another.
They had two therapists working together two days a week, clients came from the hospital therapy program and one of the therapist provided one of her two horses, also rotating them and other people did the same.
A local trainer was hired to exercise the horses twice a week, so the horses were ridden four days a week and had a stall with a run to live in and turnout also.
The horses were always well taken care of and happy to go work there and happy to come home too.
The program's insurance was part of a state grant and that was cut two years ago this month in the budget cuts, so the group had to close, until that is reinstated.
My point, not all therapy centers use their horses hard, or even own horses.
Whoever wants to donate to one may find the same in other places.