Pet Forum

There are four stages to the female dog's reproductive/estrous cycle (heat): Proestrus, Estrus, Diestrus, and the Anestrus stage. These four stages of the female dog's reproductive cycle are important for the dog breeder to understand in-depth.

Proestrus begins when the female canine swells and begins to drop blood. It can typically last from 4 to 20 days. During this period a bitch may attract males but will not accept them for breeding. It lasts an average of nine to 11 days, but can last for as little as three or as long as 21 days. Its onset is usually accompanied by a bloody discharge from the vagina as well as swelling of the vulva. Identifying these signs depends on how much hair your dog has at her hind end and how thoroughly she grooms herself. A bitch may become attractive to male dogs during proestrus, but she’ll show little interest in the males at this stage. The walls of the bitch's reproductive tract thicken during proestrus and it’s possible to collect epithelial cells (cells from the uppermost layer of the skin) from the reproductive tract of the bitch with cotton swabs to determine approximately how far along she is in her cycle.

Estrus is a very important time in the dog reproductive cycle. Estrus is the time a bitch can be bred. This can last from 4 to 13 days. Typical this is the 9th to the 12th day of a bitch's season. But I have seen bitches bred as late as the 26th day of season. Determining estrus is critical in determining when to breed (either naturally or with artificial insemination). During this stage, she sometimes exhibits a behavior called "flagging." This involves the bitch standing in one place, sometimes shuffling her feet, while at the same time, lifting her tail to allow the male to sniff her hind end. During estrus, the vaginal discharge decreases, becoming less bloody in many dogs. None of the small round epithelial cells that were typical of early proestrus can be seen under a microscope in estrus. The progesterone level continues to rise. Near the onset of estrus, there is a very short rise in another sex hormone, luteinizing hormone (LH). Once this has peaked, ovulation usually occurs within 24 to 48 hours. The prime time to breed the dog is approximately two days after ovulation or four days after the LH surge.

Diestrus is the third stage in the female dog's reproductive cycle. Diestrus lasts from 60 to 90 days in a dog that doesn’t become pregnant or approximately 63 days in a dog that does become pregnant. As a consequence of the bitch’s long exposure to progesterone when she’s not pregnant, she’s prone to a condition called pyometra if not spayed. Pyometra occurs when the uterus fills with bacteria and white blood cells. If untreated, pyometra can lead to fatal illness due to toxins secreted into the blood stream or the uterus actually rupturing. Thus, it’s highly recommended to spay a bitch that will not be used for breeding. In diestrus, the vaginal discharge will cease and the epithelial cells of the reproductive tract quickly appear small and round again. White blood cells can be seen in very high numbers during the first few days of diestrus. This is normal since their function is to clean up the cellular debris left behind by estrus.

The final stage of the female canine's reproductive cycle is anestrus. Anestrus lasts an average of four to five months. It’s usually considered a time when the sex hormones are at very low levels, although they do continue to have small rises and declines throughout this stage.If a swab of the reproductive lining is taken and viewed under a microscope at this stage, very few epithelial cells can usually be seen. Those present will usually be small and round.