I free feed my boys so I really have no idea how much they eat. I put 3 big scoops in their bowl (they share) and sometimes it lasts for 2 days and sometimes 1. I am soooo not used to a picky eater so not sure what you could do to get him to gain a little. I wonder if they make a doggy supplement for this? I know like with my neice who was under weight the dr had my sis give ensure to add a little so maybe there is a dog friendly addition like that you could do? How nice to be able to leave him with your breeder! That must make you feel like he is being WELL taken care of.