I don't have much to add to the comments, but I did want to relay a little story: I brought home a retired broodie on October 1. She was 60 lbs, which is close to her "racing weight" (61 lbs). She looked like a sausage. A few weeks of walking later, she looked great. She still weighed 60 lbs. She apparently hadn't moved much in the few weeks before adoption--she was recovering from an emergency c-section and spay. Walking was enough to build up her butt muscles and tone up the rest, and the redistribution of the weight made her look much fitter. I recently noticed that she looked a bit thin. She was 58.2 lbs. I've increased her food slightly so that she gets back to 60 lbs.