Saddle fitting is one part art, one part science and one part magic. And like anything artistic or scientific, there's an element of practice involved; the more horses you see, the more saddles you see, the better trained your eye becomes.
It is crucial that an educated and experienced professional be involved in the fitting of a saddle to a horse and rider, and by that I do not mean someone who simply reps one brand of saddle for one company.
All that said, there's something to be said for common sense. While some folks pass around the Seven Rules of Saddle Fitting like the gospel, I have a few rules for myself that I think are even easier to understand and are true more often than not.
1. Is the saddle shaped like the horse?
This isn't always so easy to see. The tree of the saddle (the wood or synthetic "frame" that gives a saddle its shape) is deep inside, and the panels (the squishy parts that make contact with the horse's back) are tacked on after, so two very different trees can look like the same shape after the panels are tacked on.
All that aside, you can still get an idea. Look at the panels. Do they make the saddle look like a banana, with the back of the saddle sweeping up and away from the back? That means less surface area on the horse, which means the rider's weight is dispersed over a smaller surface. That increases the possibility for pain.
Look at the gullet, the space between the panels that would go right over the spine. Is there a ton of space, equal from front to back, with the panels flaring away like a tabletop? Then that saddle could be a good choice for a big flat backed horse, but a terrible choice for a triangular Thoroughbred. Does the gullet look like an hourglass, lots of room in the front and back but narrow through the middle, under the stirrup bars? Then it's probably not the right choice for any horse that's got any thickness behind the withers, an area that is overwhelmingly overlooked.
2. Does it look comfy?
Give the panels a squeeze. Do they feel like Charmin, or like concrete? Hard panels are like having a hammer tapping on your back every step. Ouch.
I also always like to look at the saddle from the back. Do the panels angle away from the gullet, like single quote marks? Are they narrower at the bottom of the saddle than they are at the top, or vice versa? Panels are what absorb shock in a saddle and disperse weight. They should cover as much surface area as possible, to distribute the rider's weight over as large an area as possible.
3. When you put it on the horse, does it pinch?
General rule of thumb: Too high in front is too narrow. Too low in front is too wide.
But it's not that simple. That's only considering the front of the saddle, the part over the withers. It's easy to tell if there's wither clearance; stick your hand in there, and there you go. But what about the part under the stirrup bars, where the nuchal ligament attaches? THAT is where you get pain.
It's not so easy to do by yourself, because it's best when there's weight in the saddle, but if you're alone, girth it up tight and try to get your hand under the stirrup bars. If it's like trying to pry open a really stubborn jar of pickles, it's probably too close to that sensitive part of the back, and you may need to look for a totally different shaped tree, not merely a wider version of the saddle you're trying.
4. One size fits none.
"I can make this saddle fit any horse" is a lie. No ifs, ands or buts. Even the most forgiving of tree shapes is still a solid, welded or molded thing, and if you can think back to high school physics class, every action has an equal and opposite reaction. If your saddler widens the front of the saddle by pressing the head out, the middle of the saddle, where the stirrup bars are, gets narrower.
And most “adjustable saddles” are only adjustable at the head, the front. The rest of the saddle stays the same. Maybe you’re fortunate enough to have a horse who only gets fatter or fitter right behind the withers, and stays the same shape everywhere else, but I’ve yet to meet a horse like that.
5. Fear not the pad.
Sure, in a perfect world we could make a saddle for every horse in the world that could be used padless. But corrective pads can be a huge asset, particularly on horses who are built a little funky.
Consider Billy. At 18, he’s in stellar shape. He’s been a dressage horse all his life, and he’s strong, fit and in good flesh. He’s also, in the last few years, gotten a little lordotic – swaybacked, in layman’s terms. It’s not huge, and it doesn’t affect his work at all, but as he’s aged, his back has gotten curvier. Where there was once muscle and fat, there’s now air.
I could spend the money to get a new saddle with bigger panels, up to a point – somewhere along the line a panel gets too big to support itself – or I could get a snazzy rear riser pad from Prolite. It fills in what used to be muscle with a shock-absorbing material, returning the saddle that’s fit him for years to level. Easy-peasy.
Indy, my mom’s delightful pinto, has a very Thoroughbredy back: narrow and with high, long withers so pronounced we call him the Land Shark. Instead of trying to find a saddle that is wicked narrow in front and less-so in the middle (so as not to pinch that thick area under the stirrup bars), we got a pad with a little front riser. It basically makes him thicker in front, so a more conservatively shaped saddle will fit him without pinching those sensitive withers OR pinching the sensitive nuchal ligament.
And for young horses, who don’t stay the same shape for more than five minutes, pads are a godsend, too. I’ve found most horses get narrower as they mature and develop physically. I have a great saddle in the barn that is wide and generous, and most youngsters start out in it well.
As they get fitter and narrow, I can slip a flat Prolite pad in there to give them an extra half-inch of “weight” back, getting me another six months, maybe even a year out of the same saddle before they eventually get too narrow for it.
Ditto for horses coming back into work after time off – you don’t want to have to buy a saddle for them in their pudgy state, then have to go buy another one once he’s back in full condition.
Last but not least, all of these rules are just a starting point. Nothing, nothing, nothing is more important than having the eyes of an experienced horseman to help you, one who understands how saddles work, and how horses work, and isn’t just trying to sell you a saddle from his brand come hell or high water.