Border collies are typically skinny and naturally lean; this is because they are a tremendously active and energetic breed. As such, keeping weight on a border collie can prove a challenge; even if they are fed handsomely. Particular foods, and talking to a vet is one of the best things you can do to ensure your border collie has sufficient weight and does not become or stay too skinny (whereby the rib cage becomes exposed and is visible).