The rule is, you should be able to feel their ribs, easily.
The vet can tell by his records if he is gaining. Since you see him and lift him everyday, you might not notice.
If you have a scale for yourself, you can weigh him with that. First weigh yourself, then hold him and weigh yourself while holding him. Do that once a week and you will be able to see if he is gaining or losing.
On a 10 pound dog, one additional pound is like a 100 pound human gaining 10 pounds. |