Thank you for your reply. Perhaps the hiding is one of he answers.
I have often read that humans gain weight due to stress even if they are not overeating and I had wondered if the same thing could happen to animals.
The dog is a border collie and is a beautiful intelligent dog. He is seven months old so we will give him some time and continue with obedience classes! I really do cringe at the thought of having to give him away!
Your cat may have gained the weight because she is hiding more and not getting as much energy. I hate to say this, but you may need to get rid of the dog. If cats and dogs are not "raised" together when they are both young, many times one or both do not adjust well to each other. Give it some time and see what happens. Good luck!