There are so many grade horses that go to slaughter every week, and so many purebred. I have two purebred, registered, gorgeous, well-broke horses that I outbid the kill buyer for. My arab is especially nice, he's my $150 wonder horse, lovely 12 year old gelding, I can put my husband on him who hardly knows the front from the back. Unfortunately, no matter how much your mustang may get false pregnancies, the horse market is very poor. There is a hormone available that eases the mare's cycles. It's really cheap and I bet it would be of great aid to your mare. Ask your vet.