lab mix gaining weight

Question
Hi I have a 1 1/2 year old lab mix. He is on the smaller side, we think hes mixed with a terrier like a jack russel. His weight and size stabled off at about 9 months, he was about 40lbs. But recently we've noticed that hes putting on some more weight. He seems to be bulking up around his ribcage. We have not changed his food or diet in any way. We were just wondering if this is typical of labs and lab mixes and if we should be concerned. Thank you!

Answer
I think often it happens a little sooner, but you do need to take action.  Your dog definitely should be narrower at the waist than the hips and chest. You should be able to easily feel the ribs, but not see them. Each dog is different. Standard recommendations are a good place to start, but each dog must have its food and exercise adjusted to its individual needs. Here is a link to a good illustrated guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx