Ah! You're probably going to let your pets have happyness points rolling in?
Well, I can help you out a bit with that. If you have the Limited Edition of Pets you can buy at the Pet Store a special salt thingy that, when the horse licks it, provide the horse with a possitive +10 or +15 moodlet, I can't remember it correctly. It will stay there for some 8 hours I thought, which is pretty need.
The horses will lick it automatically, they can't lick it twice when the possitive moodlet is still active.
The horses (and I thought dogs and cats as well) really enjoy it when you're going to brush them. They will get a nice moodlet from it. A bath works also, if your sim has a good relationship with the pet. And taking care of the heeves of a horse also provide a good moodlet.
I think that they will be happy to, when they play with the ball, but I'm not sure about that.