Just a point here that you may not realise.

Just because I may have deleted a horse from the lists this month because of injury or something, does not actually mean that you HAVE to take it out of your stable. If you already have a horse in your stable, you can theoretically leave it in there for as long as you like, no matter whether it's injured or spelling or retired or whatever.

Obviously, if it's a horse like Grand Armee, you'd be pretty damn silly not to swap it as it takes up $850,000 of your salary cap. However, with an inexpensive horse that I delete from the lists, you may decide that it's actually a better tactical move to simply leave it in there and instead swap another more expensive horse from your stable. Of course, you won't get any prizemoney from the horse, but you may still decide that it's worth doing.