How to Ride Bareback on a Bony Horse
Most people ride with a saddle most of the time. Bareback riding, however, can be fun, especially in the summer. Some people hop on bareback because they can't be bothered to get a saddle, or are only going a short way. Others might be planning on taking the horse swimming. Some riders may ride bareback because their saddle needs repair or they are looking for a new one that fits better.
The truth is, though, that some horses are simply better built to ride bareback than others. Cobs and draft crosses can be particularly comfortable. Narrow horses, however, often have a spine that sticks right up where you don't want it and many Thoroughbreds and crosses have the infamous "shark fin" withers (associated with speed) that make saddle fitting difficult and riding bareback extremely uncomfortable.
Problems From Riding a Bony Horse Bareback
If your horse has a bony spine or high withers, riding bareback can be extremely uncomfortable and can even have other unfortunate effects.
I once made the mistake of hopping on a sixteen-hand Appendix Quarter Horse (Quarter Horse-Thoroughbred cross) without a saddle—the day before my annual physical. When the doctor saw my private parts she almost went and got the rape kit! I'd bounced right into his huge bony withers and bruised myself in places normally associated with sexual assault! I'd hate to think what would have happened if I'd been male...other than "Ow."
So, yeah, you can even pick up minor—but painful—injuries from trying to ride a bony horse without a saddle. Is there a solution other than picking a different horse?
The Obvious Solution
The obvious solution is a bareback pad, although these can be pricy. A bareback pad will give you quite a bit of padding. It will also buffer the horse's sweat and shed hair, which is helpful since riding bareback can soak your breeches on a hot day or cover them with hair if it's spring. When I was a kid, I used to throw a towel over the horse's back, although this doesn't help with padding much. If you do use a towel, use a thick one; they grip better.
If you don't have a bareback pad, then you can use a saddle pad, although this might slip. If you have a blanket surcingle, then the combination of that and a pad will work. However, since most modern blankets don't require surcingles they can be hard to find these days. Some people ride on top of a blanket, but I don't recommend this: Modern blankets are often designed to slip easily if the horse rolls, to reduce the risk of the horse becoming tangled. Riding on a blanket may also put extra strain on the straps and reduce the life of your blanket.
Some people, however, argue that using a bareback pad is cheating. So, what are some other things you can do?
Topline and Condition
Your horse may be bony for a reason. Horses that aren't ridden that often, aren't ridden correctly, or haven't been ridden in a while often have less muscle across their spine, which then results in boniness and prominent withers. In some out-of-shape individuals this is compensated by fat, but not always.
Getting your horse in better shape, therefore, can do something about the "bony spine" problem, and is good for your horse anyway. Going up and down hills will help your horse's top line and overall fitness a lot. Always riding the horse correctly front to rear also makes a difference. Your horse should be stepping further under himself when you're on top than when at liberty.
The only other thing that helps is practice. You may want to go from saddle to pad to nothing in graduated stages. If your legs are strong and you have a good seat, you won't bounce up and down as much, and are far less likely to end up bruising embarrassing places.
Learning to ride well bareback will help your seat in general. It really helps with developing the "velcro seat" and becoming that rider who never seems to come off no matter what the horse under them does.
Be warned, though, if you aren't used to riding bareback you are likely to get saddle sore, even if you don't when using a saddle.