Hi my BC is the same. I got so worried by his leanness and asked my vet was there anything i was doing wrong. He only now weights 19kg, very picky with his foods and is very active. I cant feed him wet food or we have bowel issues so we feed him dry food. My vet said she wasn't worried due to him having good rib coverage and good muscle mass in general hes very fit. she recommended i put him on a worker diet to try and keep what weight he does have on him x