Fatty beef, lard, eggs, milk, fish, lamb, a slice of whole meal bread every meal. All these will put weight on a hard worked dog ... dogs get their energy from fats and springers are busy dogs at the best of times ... if yours has the space to be active all day it's going to need more of a source of energy ... because it hasn't got enough fat in its diet it is starting to deplete its own body to get the energy it needs ... change of diet is the only answer ........