Why Does A Dog Gain Weight After Being Spayed Or Neutered?

I have noticed with my other dogs that after being spayed their belly started to sag, why is this?

 When we spay or neuter a dog we are actually removing organs and stopping a lot of hormone production. This leads to a change in metabolic rate since the dogs body is no longer supporting those organs or their function. You should reduce the dogs intake by about 10% after recovery from the surgery to prevent the weight gain that you see as a sagging belly.