[help] dog weight question

My dog is a four year old, neutered spaniel/border collie mix. When we adopted him, he was 55 pounds and overweight, shaped like a bit of a barrel. He'd been at a shelter for quite a while. When his last owner had turned him in, the shelter vet had registered him at 46 pounds. Now he's gotten slimmer. He has a visible waist, a tummy that tucks up and I can feel his ribs (although not as well yet as I maybe should). But for some reason, he now weighs 61 pounds :O Also, his chest is so much broader now that the harness I originally bought for him doesn't fit anymore.He has a fitbark activity monitor, so I'm keeping track of his calories and he's not overfed. I feed him a good quality kibble and make sure he has enough activity. There are stairs in the house, and he has a game where he takes a toy to the top of the stairs, throws it down the stairs and then fetches it to do it again. He gets some extra exercise doing that, too.He seems very healthy, but I find the weight gain to be weird? I'd love some thought on this. via /r/dogs http://ift.tt/2rHMMLH