I don't breed dogs for a living, my dogs are family pets. I have 2 girls and a boy. The girls will hopefully have 2 litters before I get them spayed, and I leave at least a year between each litter.
One girl is 4.5kg/10lb and she's small, so I have to find an equal sized mate for her. My other girl will mate with my boy dog, he's 12 in July.