
Some excellent breeders have quite a number of dogs, and 10 wouldn't be considered a large kennel, especially if a lot of the dogs are oldies.
If a breeder has a puppy a year or two and keeps each until its death then they would very quickly have 10, as they can live to 15 years.
When my youngest bitch has her litter I will have five dogs, all living in the house, and this is really as many as I can keep in an average domestic set up without kennel facilities and land, if I wasn't strict with myself I could easily have more. my girls range from nearly four years to 11 1/2 years, I don't keep males, as I would not be able to seperate them when the bitches are in season.
Also when a larger number of dogs is kept they often have paddocks/runs where they spend their time outside, and usually rotate with indoor time. some breeders keep their old dogs as indoor dogs and young ones as kennel dogs. All may be really well cared for and loved.
On the other hand you could find a breeder with one dog and one bitch kept purely to produce puppies at each season, no sign of breeding to establish a line and improve the breed.
A breeder will use whichever dog is the best mate for a particular bitch, and this is often not a dog they own themselves.