minature ponies

Question
I have two ponies, age 9 to 10 yrs, that we pull at contests, when working ponies they can't seem to put on  weight have tried every thing they are turned out on paster, mixed grain three times a day, also hay,  have tried weight builder, joint supplement are given, beet pulp, afraid they will founder.feet are reset every month.
What would you recommend?
When we go to pulls other ponies with same frame structure are so much heavier than them.
Thanks.

Answer
I would love to see the ponies pull. Thats very neat. I bet they love it. Are the draft ponies? Do you live in the midwest?
The first thing that comes to mind is that the ponies may have parasites. Parasites are a very common thief of nutrients. They will take from the ponies before the ponies get a chance at what they have eaten. What is your deworming program? You certainly have tried most of what  I would recommend to try. I hope we can get this figured out.