i'll have to stay out of this one, we have over 4 dozen.
The first time I read this I didn't process "Oh, she has a lot of horses.", as an owner of 3, all I got was "Ohhh, she buys a LOT of feed."
I've done more "liking" in this thread than I have in a while..Great posts by SR, MM, MHF, and Kait..Love it.
OP, I really, really don't understand how you can say that it's abusing one horse's training when someone owns multiple horses. I own 3 QHs and they are my life, I have a 22 year old retired gelding, and two 12 and 13 year old mares.. Now, up until last year my gelding still would occasionally run barrels. He is an absolute spoiled brat and is a fantastic Supervisor now..I still ride him frequently, bareback and under saddle. He still gets a good bit of ground work and isn't neglected in anyway..If anything his fat butt lives better than a ton of horses out there...When it comes to my girls, I barrel race both of them. Nikki and Lark both bring a VERY different set of cards to the table and have different things to offer. Does that mean I love one more than the other? No..They are equally cared for and not abused in any way whatsoever. They are all ridden multiple times a week and worked as their own "person", not as just a general horse would be. They have their own personalities and it's a huge pleasure to watch all of the gears click into place when working those individual horses and our little goals coming together.
I also think that riding and caring for more than one horse makes you, as an owner/rider, a better and more experienced horse person. Riding just one horse, you get comfortable with that horse and you haven't experienced those different traits of different horses.. I've ridden every Western discipline and dabbled in English..I now barrel race full time but I seriously think that riding and showing all of those different horses and disciplines MADE me the rider I am today. I'm not just stuck with one set of skills, I can play those different cards and skills when riding my different horses..
As for owning multiple horses, like others have said, horses are herd animals. You can't expect one horse to really be happy on it's own. You aren't in it's "herd" at all times and can't replace that herd by being your horse's friend. That animal interaction is still needed between horses..