Proestrus
Small Dog, by jbcrussell
Proestrus. Proestrus is the stage of getting ready. This is the time when a bitch's reproductive tract is preparing for the possibility of breeding with a male dog.
Proestrus is what is happening when we observe a bloody discharge from the dog's vulva. This is the result of the loss of red blood cells by leaking of the blood vessels in the uterus as it prepares for mating.
During proestrus a bitch may become attractive to males and she may play and interact with them, but she will not allow mounting or mating to occur.