weight gain

Question
i have two black n tan german shepards aged 3 1/2 years n there brothers i feed both the same amount of meal in the morning and night but one of them can not gain weight and u can see his ribs he's always been like this even if i feed him extra food he also has not got great back legs he never came up on them properly but he's still a very strong dog the vet told us when he was a pup we'd probably have to get him put to sleep but he has improved but could improve alot more and i'd appreciate any suggestions and help you could give me on this matter. thank you

Answer
As long as you are feeding a concentrated, meat based chow, and the vet can't help, there may not be much you could do.  You could try one of the working dog chows, or even a calorie dense puppy chow.  Feed him as much as he will eat.  Different dogs need different amounts.  You may have to accept his ribs showing a little.