Need help on how to fatten my pony up and build some muscle!!!!

Hi I just got a new welsh d pony about three months ago and she was from a dealer so she was quite thin. She was broken in a trap so we had to train her how to canter and all! I need her to put some more weight on and build up some muscle so she can be a wee hunter pony! Any suggestions?
Thanks in advance

Where are you located? What kind of diet is the pony on now? (hay, feed, supplements) How much working will the pony be doing?

Im in northern ireland lol and she is getting 1 1/2 small green scoops of cool and conditioning mix and a packed haynet of haylage and at the moment she is doing dressage, working hunter, show jumping, M&M classes, x country just everything I can but quite small :)

Many think that a 11-14% protein diet high in fat helps. Really it is quite the opposite. You need to find a high protein, low fat, medium fiber feed. It may be a slower process, but quite a bit more healthy gain.

Think of it this way.

You have two options, fat or protein. McDonald's or home-baked chicken breasts. Sure, you'll gain faster by eating at McDonald's versus the real meal, but imagine how much harder your body has to focus on processing that fat into energy and turning it into muscle, instead of starting with protein, eliminating the body's need to process all the fats. If you'll start with the protein, the body absorbs and uses it for energy that in turn builds HEALTHY bulk faster than packing on fat and trying to turn it into muscle.

The feed I give my mare and gelding is a 32% protein, 7% fiber, and 5%fat. They are high activity, and are NOT hotter on this feed. (they feel better, act better, and look better. They are truly themselves.)

Thanks very much will take that into consideration and try it out thanks again :)