Is my horse ever going to fill out?

Weight looks fine to me. You need to remember that you can't change a horse's conformation. If the horse has a narrow chest and small rump- then they will stay that way throughout their whole lives.

They DO need more muscle. As the other post said, you need to up their exercise- and that will fill out their top line and make them look more rounded.

A good indication of weight- you should be able to FEEL the ribs, but not see them. If you can't see their ribs, they are more than likely the right weight.

So yes, just need more muscle!

The vet's right...just the right weight. I don't know what you are feeding her, but she could use more nutrition and muscle building. Longing, going for walks, up and down hills, over logs...training on the trail and don't use that saddle if it fits her like that. You want it to be a good experience. Supplement minerals and vitamins. I can see that she needs them. She also needs 2.5% of her weight in hay/day. If you can get that vit/min. mix with a flax base, then that will put the shine on her.

If she's not getting fatter, then she's using it to grow. I prefer a horse that grows evenly like this. You're not at risk of having to fight the fire of physitis. Since you see her everyday, its harder to notice this growth. Its not fair to compare her growth with the other horse. It's a genetic thing. In the end, you will find that she's easier to mount, cattier with her movements and has virtues that the other horse doesn't and vice versa. Think of them as two different horses in all things, because that's exactly what they are.

That's the horse's conformation. Just because they are a quarter horse or a paint doesn't guarantee they will be stocky bulldogs.

Your black horse might pack on some more muscle and bulk, but she's not going to be a wide stout horse. She's more petite and dainty and no matter what you feed her, the conformation will not change.

I have to agree with everyone on her weight looks fine, and they you really can't change conformation.

But you might be able to help her "fill out" some.

Are you working her regularly? I know when my TB was at a decent weight, he still looked "skinny" even though he really wasn't. Riding and working them help rebuild the muscles that they don't use. If your riding 15-20 minutes a day doing walking/trotting exercises, there might be a chance she'll build muscle and fill out. My horse did and he looks amazing now. :D

Good Luck.

Not very good pictures but I can tell you the red one is probably about 15 hands and the black one is a lot shorter that that. 15 hands is 60" there is 4 inches to a hand.