I'm a first-time rabbit owner, have had my minirex for over three years and I was shocked at how lean and lanky they are. I could feel his ribs and bumps in his spine, but the vet said he was a good weight at 4.5 pounds. (Just over 2 kilos for the rest of the world) Though if you are that concerned, like others are saying give some extra pellets to be safe until the vet weighs in.