Putting weight on...and KEEPING it on!?

I have a coming 6yr old APHA mare standing 14.3hh and weighing in at about 900lbs. She is built very lean, but does muscle up nice. She is leggy but thin, and is always ribby. Like I said, she is built lean but it bothers me and I have done everything to get weight on her, I would just like some opinions from others about the best possible options.

Right now she is on a certified high mountain grass hay (very rich, she can't be on alfalfa because she is prone to colic) as well as XTRME grain which is a 12% crude fat grain/oat mix. She loves both and this is the most recent combo we have had her on. For awhile she was eating Safe Choice, but it didn't do anything except make her a bit hot and she didn't seem to be gaining any weight. This current combo she both likes and seems to be putting on a few pounds, but Im not sure that alone will do the trick.

Someone told me that Rice Bran is perfect for both weight gain as well as getting a coat/mane sheen and slick. I would like to try it out, it supposedly works very well and cuts your grain bill in half...but I am just worried about switching and trying too many things as well as the fact that a bag lasting only 2-3 months runs about $76.99 around here.

Before anyone says vet check etc, she has 6 month check ups and is UTD on all vaccines, worming, floating etc and has been passed by my vet as healthy. I would just like to see her put some weight on and not be so ribby as we ride hard all spring/summer for trails as well as shows and competitions every to every other weekend...any suggestions would be great, perhaps your own horse stories to go along with? Thanks so much and God Bless.

If you've resently changed her diet, give it a month to see how she responds to it. It's all about adding more calories. She might also benefit from extra protein to build up the top line. Just adding the high fat feed might do the trick. Rice bran is not the silver bullet. It only has 20% fat and is high in NSC. I wouldn't add more than a cup per day. You're better off adding roasted soybeans, 20% fat, 40% protein and $20/50#, flax seed 38% fat, 24% protein and $32/50# (great for coat and skin as well) or just top dress some veg oil 100% fat. Have you ever tested your hay?

I've had good luck with adding Wheat germ Oil to my horses grain. They get about 2-4 tbs per feeding. The oil is very high in fat, about 98% or so if I remember right. It's never made mine "hot". I'd also add a few flakes of alfalfa to her diet.

I agree with Horsecrazy and Percherons. Maybe try beet pulp, it helped my mare a lot :)