The saddle is much too narrow for the horse.
Here's how I check if a saddle fits: 1.) Check the gullet.
The area in the front - the gullet - is THE most critical measurement you can make in a saddle because it tells you about what the angle of the bars are and helps suggest what kind of bars the saddle may have. We use the conchos on either side of the gullet as the measuring place, just because there's no real industry standard, but all saddles have these points and they're all about in the same place. These conchos are screwed into the the top outside front of the bars, where the bars are supposed to first make contact with the horse. The position of these conchos should be roughly on either side of the withers, just above the shoulder. In your pictures, you can see that the conchos actually sit quite high above the horse, indicating that instead of the inside top of the bars making contact behind the horse's shoulder blade, it's the middle/lower inside of the bars making contact. This means that the saddle is too narrow, which will result in pinching of the withers (and can lead to permanent psychological and physiological damage for the horse).
Picture 1 here is a side view - you can see where the conchos sit on either side of the withers instead of up above. (This is my Big Horn...it gets used A LOT so look past the mud and dust. Lol Also, it's sitting just a tad forward because it's a 7/8 rigging, but that would correct itself once I cinched it up).
Picture 2 is another way we can get a good measurement on whether or not the saddle is too wide or too narrow. The "3-finger rule". If you can fit 3 fingers comfortably inside the gullet, the gullet fits nicely. Remember that when you actually sit in the saddle, you're going to lose about an inch of space in this area. So if you can only fit 2 fingers but not 3 comfortably, it's too wide, but if you can fit more than 3 fingers, it means that the gullet is too high, meaning that unless it's a gaited or arab saddle, the bars are set too close for the horse's shoulders. I.e. They're pinching the spinal chord. You can see that my fingers are right down the very top of my horse's withers all the way in. Now, in the very front of the gullet some saddles are designed to be more open and "yawning". This isn't what you measure. You measure the lowest part of the arch, wherever it is. 2.) Check the shoulders and the twist.
Once we establish that those 2 elements fit correctly, we need to check other things. I usually move on to the shoulders to check the twist. The saddle's twist is the angle of the bars as they meet the pommel at the shoulder. The skirt of the saddle should actually look like it's over the saddle, but if you stick your hand under it, you should feel that the bars rest just slightly above and behind the shoulder blade, so the shoulder can have free range of movement. If the saddle is too narrow, instead of using the horse's entire body to distribute the load weight, it'll be like someone giving you a charlie horse right behind your shoulder blades. Ech. But while you're at the shoulder, look down the saddle and see if it follows the contour of the horse's body. It should look natural. There shouldn't be any angles between the horse and the saddle - one just flows into the other. Big Horns are cordura, so the skirts get rumpled. It doesn't matter what the skirt of the saddle does, what matters is the bars, which are right up under the seat of the saddle so that's what we're focusing on. What happens on the lower edges is usually cosmetic (Because the bars don't extend that far down and it's all flexible material down there). 3.) Check the bars against the back (flare).
The bars of the saddle are probably the hardest to check, but give the stirrups a flip and see how the saddle's fitting against your horse's body (flare). Try and run your hand under there, too. The saddle should not be putting any pressure directly on the spinal column. The bars of the saddle need to be at the same angle as the horse's rib cage because that's where it's supposed to rest - on the top of the rib cage. Too wide and the saddle sits right on their spines. Too narrow and only the bottom edge of the bars sits on the ribs - imagine carrying a camping backpack with 2x4s for a support system...the "2" part on your back supporting everything. When you stick you hand under there, if it fits right it'll feel kinda like it does on the horse's back. You'll feel the weight of the saddle, but it doesn't hurt. It doesn't feel like anything, really, and that's how it feels to a horse, which is a good thing. But if you feel like your hand is going to sleep or that part of it is getting more "push" than another, something's wrong. Lean your arm on the saddle (or have a friend do it)...now you might be able to REALLY feel if something's amiss. If it feels like it digs or if it's not uniform pressure, your horse will feel the difference, too.
Here you can sort of see that the bars (the puffy part of the cordura right under the seat) are resting nicely below the spinal column, right on the part of Ranger's back where it's sort of flat..the top of the ribcage)...it's not the greatest picture, though, because the stirrup being flung over the other side are picking up the rest of the saddle a little. But you get the idea. 4.) Is the seat level?
The last thing I check is to make sure that the saddle's seat is level. I check everything else first because there's no point in checking further if the others don't fit, first. I use the level seat as confirmation that the saddle fits well (as long as everything else checks out). If it's not level, then I may have measured something wrong, or the horse may have shifted the saddle and I didn't notice, been resting one leg when I checked something, leaning to one side, standing on an incline or unlevel ground, etc. Don't actually look at the seat, itself, though. Some saddles have barrel cantles, some have equitation cantles. I have an old, old show saddle with an equitation seat and a big rise (the part of the seat that swells up behind the pommel). Look at the contruction points of the saddle (screws, bolts, nails, conchos...whatever is holding it together). Those are the most important. If the seat is level, the bars are level, and it's the bars that we care about. In your saddle, you can see how the back of the saddle isn't anywhere near the horse's back, where it should be. It's actually making the saddle tilt forward, not because the gullet's too wide, but because it's too narrow. The one spot where the saddle is "pivoting" off the horse's back is carrying all of the weight of the saddle and yours.
Here you can see the yellow line represents the level seat. I've drawn it between the two screws that Big Horn uses to fasten the seat and jockeys to the bars. My rigging is 7/8 so without the cinch being fastened, this is how the saddle sits. If I had fastened my cinch you'd see the front screw slide to where it's supposed to and drop right down into line.)
One final thing...All over the internet (and with the people I know) I keep hearing about the sweat on the horse's back. This is a myth, and a dangerous one to use as a gauge to see if the saddle fits. I have to work with people whose saddles are clearly too big or too small, and every one of them has a uniform sweat after working...and that's what they use to justify not changing their tack. Consider this: if a saddle is too wide, that means that it does not fit snuggly against the horse, so when you're riding, the saddle WILL shift from front to back and it'll do it as the horse moves. When you take the saddle off, you'll still see a uniform sweat because the saddle has been moving around. If the saddle is too narrow, then it perches on the horse's back and teeters (shifts) from side-to-side. Same situation. The saddle is moving, and the sweat follows it. The sweat theory only works when a saddle doesn't move, but we can't really guarantee that it didn't move at all. Girths become loose, and we're human and don't have perfect balance. If you even shifted your weight once, it moved and now the horse is sweating there. Even well fitting saddles need to be given "the in-saddle twist", and if they do it, than the bad fitting tack does it for sure.
If you bought the saddle from a "discount wholesaler", they are THE WORST! The saddles are made in Asia or India, and they haven't got a clue what FQHB or SQHB actually means. They're just wage earners who probably have never even seen a horse up close. There's no industry standard on what, exactly, a FQHB or SQHB is, but the differences are really only within quarter inches for gullet widths and single degrees for bar angles, but they are never as far off as your saddle is from the "norm" (if they said it was full bars).
Again, didn't mean to write a book, but I know that buying a saddle is like buying a bathing suit. YUCK! It's such a nightmare!! It shouldn't be, but it is. I've lived my fair share of the nightmare, so I try to help as much as I can. It's really important that your tack fit properly. I could write a dissortation on the psysiological affects AND the psychological affects of ill fitting tack on a horse...maybe I'll save that for another post. LOL