Do we think that animals are affected by the removal of their uterus/ovaries/testicals?

I've always thought of this, wondering exactly what the animals feel after a spay or neuter. After all, a man wouldn't be quite a man without his... special place. When Michael Vick was arrested, I was really hoping that they would go by popular demand and neuter him, for the sake of science. After all, everyone wants to know the true effects!