I feed my girl Solid Gold Wolf Cub LBP. However, many of the members on here can give you better ways to gain weight than switching to puppy food.
Also, what is your pup's weight? Height? He may not be underweight. It is better to keep them slim than overweight. Can you post a pic?
SBD Posejpal's Leyna, HCTs 6/16/2010
SBD Posejpal's Hades, 5/9/12
At the rainbow bridge:
Zappa 12/27/00-1/23/12 You are my heart, my soul, and my best friend. You will be with me always.
Zeus 5/9/12-8/13/12 You taught me strength. Run free.