When your female dog enters puberty, she begins her estrous cycles, commonly known as heat cycles. This intricate process involves four distinct stages, with proestrus and estrus being what most people recognize as “coming into heat” or “coming into season.” Understanding these stages is crucial for breeders planning a litter and for owners who wish to spay their dog to prevent unwanted pregnancies or future heat cycles.
When Heat Cycles Begin and Their Frequency
A dog’s first heat cycle can occur anywhere between 6 to 24 months of age. Generally, smaller breeds tend to start earlier than their larger counterparts. Most dogs experience two heat cycles per year, with an average interval of 5 to 11 months between them. However, some breeds, like the Basenji and Tibetan Mastiff, are exceptions, typically cycling only once annually. The most prominent indicator of a dog in heat is bloody vaginal discharge, which usually persists for 14 to 21 days.
The canine estrous cycle comprises four stages: proestrus, estrus, diestrus, and anestrus.
Proestrus: The Initial Stage
During proestrus, a female dog’s ovaries produce estrogen, with levels peaking one to two days before the onset of estrus. This elevated estrogen causes a swollen vulva and bloody vaginal discharge. While dogs in this stage may exhibit attractive behavior and playful interactions with males, they are not yet receptive to mating. Proestrus typically lasts for an average of six to eleven days.
Estrus: The Breeding Window
Estrus marks the period when a female dog becomes receptive to breeding. This stage is generally initiated by a surge in luteinizing hormone (LH), driven by decreasing estrogen and rising progesterone levels. These hormonal shifts dictate the female’s willingness to mate. Although the vaginal discharge may change to a straw color, individual variations are common. Estrus usually lasts for five to nine days but can range from one to twenty days.
Diestrus: Post-Estrus Phase
Diestrus begins once a female dog no longer displays signs of estrus, such as allowing mating. This stage is characterized by elevated progesterone levels, which peak around 2-3 weeks after ovulation. Progesterone, the hormone responsible for maintaining pregnancy, remains high for an additional 1-2 weeks before gradually declining over 10-30 days. Importantly, progesterone levels increase during diestrus regardless of whether the dog is pregnant. Female dogs are no longer attractive to males and will refuse mating during this phase. The external genitalia in diestrus are indistinguishable from the subsequent stage, anestrus.
Anestrus: The Resting Phase
Anestrus is the quiescent period a dog enters after her heat cycle concludes or following a litter. Throughout anestrus, progesterone levels remain low. Following a normal heat cycle or whelping, the uterus undergoes a crucial process called involution, which takes approximately four months to complete. This process repairs the uterus, preparing it for future estrous cycles.
Optimizing Breeding Timing and Preventing Pregnancy
For those interested in breeding their dog, consulting with a veterinarian is essential. Your vet can perform tests, such as vaginal cytology or hormone level analysis, to accurately determine your dog’s current stage in the estrous cycle. This information is vital for successful breeding.
If you do not intend for your dog to experience heat cycles or become pregnant, the most effective method is spaying. This surgical procedure removes the ovaries, and often the uterus, thereby eliminating estrogen and progesterone production and preventing heat cycles. Spaying also prevents pyometra, a serious uterine infection, and significantly reduces the risk of mammary cancers. Owners seeking to prevent heat cycles should explore information on mammary cancers to understand the full benefits of spaying.
Rescheduling a Spay Procedure During Heat
If your dog is currently in heat, it is advisable to wait approximately two months after the cycle concludes before proceeding with a spay surgery. While a spay can be performed during heat if necessary, waiting allows hormone levels to return to their baseline, leading to a simpler surgery with a reduced risk of bleeding. This health topic was developed in collaboration with the Cornell Richard P. Riney Canine Health Center and Embark Veterinary, Inc. For insights into hereditary health conditions, please visit our genetic disease resources page.
