Ahh, very simple then!
It's an eyeball and feel test, you should be able to feel his spine and all his ribs but only able to see two of his ribs. There should be what's called a "tuck" behind the rib cage which is a narrowing of the body like a V. Much like the ideal proportions on a male human, broader chest / shoulders, narrow waist.
Feed him more or less to stay in that range, the food estimate on the side of the bag are just that "estimates". Just like the recommended food intake for humans, doesn't matter as long as they're getting all the essential nutrients and a healthy weight.
ETA Of course humans aren't a perfect comparison as they can eat poorly enough despite their weight, exercise levels, and essential vitamins and mineral intake to give themselves diabetes like Patrick Peterson. But I don't think that's an issue here lol.
Last edited by Tennessee; 07-25-2017 at 05:03 PM.