lizbud, how is the cruciate problem?

All you doggies on the D word, stop making it hard for your people!!

Seriously the less of an issue you make of it, the less the dog will notice. It takes them around two meals to get used to the lesser amount of food they can expect and after that they aren't really hungry but are playing to the audience!!
For those that are do the D for hip problems try taking the dog swimming - geat excersise without the strain.
Add fibre to the dog's diet with a handful (small!) high fibre cereal (we have All Bran and Bran Flakes).
Give up the idea that treats are good for your dog - the only one they are good for is YOU! It doesn't matter if it is bacon fat or carrot...dog's don't need treats! Of course they will always take them, that's how dogs are built, but it is much better for your relationship to give rewards in the form of games, physical contact and verbal praise. You will actually like your dog even more when it does what you ask for a cuddle rather than only if you have that special biscuit.