What happens if a female dog never has puppies?

A female dog not having puppies causes no harm to the body; rather, having puppies increases physical burden and changes the figure. But if she neither has puppies nor is spayed, repeated heats over time raise the risk of uterine fluid, pyometra, and mammary tumors, shortening her life.

Therefore, if the owner has no plan to breed her, spaying is recommended as early as possible.