why does my dog have hard knots on her breast?

why does my dog have hard knots on her breast?

Take her to the vet and have these lumps fine needle aspirated.

Circumstances? If she's nursing a litter she could have mastitis. However, if she's not, I'm afraid you must get her looked at as soon as you can because if these are on the mammary glands, it is possible she has tumours - mammary cancer. Obviously the sooner you get a diagnosis, the better. It's not necessarily end-game - cancerous tumours can be removed, depending on the age of the b itch.