My TB is a hard keeper. When I had him at the barn, he was on a dry lot for a few hours a day and then stalled for much longer. So I can see why it was difficult to get weight on him.
Then I moved him to a farm and on 25 acres of pasture - he get full range of grass in the summer, and during the winter he is on free feed of round bales.
I feel him Purina Senior. He gets 4 pounds a day. 2 in the A.M and 2 in the P.M and he is doing really, really well on this program. Very well.