Could your dog be lactating because another dog is pregnant in the house?

A dog should only lactate (produce milk from her mammary glands) if she is about to have puppies or is actively nursing puppies. However, a non-pregnant dog may lactate due to a pseudo-pregnancy; when the reproductive organs reset to "not pregnant", the lactation will cease as well. There is a slight risk that the lactation could be due to a medical issue such as a tumor or infection, so it may be helpful to have your dog seen by a veterinarian.