Border Collies do tend to be REALLY lean teenagers. Gonzo was SO skinny when we adopted him, and it took him several months to gradually get to a healthy weight. You don't want to just pack on pounds, you want to build muscle and let him fill out slowly. ;] I can't find a clear picture showing Gonzo's size... plus he's pretty furry. He has a defined waist and his tummy is tucked. He has no fat on his tummy. If I place my thumbs on his back and run my fingers down, I can clearly feel his ribs with a very thin layer of fat. I can just barely feel his hipbones. And, he is a 6 year-old BC! A 1 year-old BC is typically very lanky.

Instead of puppy food, I would add good sources of meat & fat to his diet. Raw Meaty Bones (especially chicken quarters & pork) can add some healthy calories to his diet, fed a few days a week. Satin Balls are also a good way to add calories in a healthy way (do a board search for the recipe... it's mostly ground beef).

Taggart is super-duper cute, btw!!!