Heat is the part of a dog's reproductive cycle where hormonal changes cause swelling of the vulva, bloody discharge, and eventually a period where she can mate and become pregnant. Here's what you should know about when it comes, how long it lasts, and what's normal during it.
When does a dog have its first heat?
The first heat often comes around six months of age, but the timing varies considerably with size and breed. Large and giant breeds may have their first heat considerably later, some not until close to two years of age.
The first heat is a sign that the bitch is approaching sexual maturity. It does not mean that she is fully grown or that it is a suitable time for mating.
Signs that your dog is in heat
- swelling of the vulva
- bloody discharge, often spotted as stains on the floor or in the dog bed
- that she licks herself more than usual
- more frequent marking on the trip
- that male dogs show clear interest
Some bitches keep themselves very clean and lick away the discharge, making the bleeding easy to overlook. Dog panties are available and can be handy for limiting stains indoors.
How often and how long does the term last?
Most female dogs come into heat approximately every six to eight months, or about once or twice a year. The interval varies between individuals and breeds.
The actual heat period – the visible part with swelling and discharge – usually lasts around three weeks, but there is a lot of variation. Older bitches do not stop having heat as humans go through menopause, but the intervals can become longer over the years.
The bitch's reproductive cycle
The cycle is divided into four phases, only in one of which can the bitch become pregnant.
Proestrus – pre-estrus
The vulva swells and there is a bloody discharge. Male dogs show interest, but the bitch rejects them. She cannot become pregnant during this phase.
Typical duration: around nine days, but from a few days to three weeks.
Estrus – heat
The bitch becomes receptive to mating and moves her tail to the side when a male dog approaches. Ovulation occurs during this phase. The discharge often becomes lighter, more watery or straw-yellow, but this varies between individuals.
Typical duration: around nine days, but from a few days to three weeks.
Diestrus
The progesterone-dominated phase after estrus. It occurs whether the bitch is pregnant or not, and the hormonal picture is largely the same in both cases.
It explains two things that many owners wonder about: why a bitch who has never been mated can get imaginary pregnancy, and why uterine inflammation typically develops in the weeks following menstruation.
Typical duration: two to three months in a non-pregnant bitch. If she is pregnant, pregnancy occurs throughout this phase.
Anoestrus
Reproductive rest between cycles. It is the length of this phase that largely determines how often the bitch comes into heat.
Typical duration: highly variable, usually several months.
| Phase | What’s happening | Typical duration |
|---|---|---|
| Proestrus | Vulva swelling, bloody discharge, male dogs interested | Often around 9 days, highly variable |
| Ostrus | The bitch may be receptive to mating, ovulation is occurring | Often around 9 days, highly variable |
| Diestrus | Progesterone-dominated phase, regardless of whether the bitch is pregnant | 2–3 months |
| Anoestrus | Reproductive rest before the next cycle | Several months |
When can a bitch become pregnant?
The bitch can become pregnant in estrus, but the timing varies significantly between individualsShe may be fertile for several days, and both the amount of bloody discharge and the number of days since the bleeding started are unreliable clues.
Calculating your "safe days" therefore does not work as contraception.
When planning mating, the veterinarian can use vaginal cytology and repeated progesterone measurements to assess the timing much more precisely. Read more about reproduction and insemination.
How to avoid unwanted mating?
The most important thing during the heat is to prevent contact with fertile male dogs. Keep the bitch on a leash, avoid areas with many stray dogs, and expect that the recall may be worse than usual. Male dogs may take considerable detours to get to a bitch during heat.
Has the bitch mated by accident: Contact your veterinarian as soon as possible. Do not attempt to forcefully separate the dogs if they are stuck after mating. Your veterinarian can assess further follow-up and what options are available.
Imaginary pregnancy after term
Because the hormonal profile is approximately the same in pregnant and non-pregnant bitches, a bitch that has never been mated may develop signs of pregnancy. This typically occurs a few weeks after the heat.
- swelling of the udder, sometimes with milk production
- nest building – she digs in carpets or makes a nest
- that she carries and guards toys
- restlessness, clinginess or changes in appetite
Mild cases resolve on their own. Contact your veterinarian if symptoms become severe, if milk production is significant, or if the udder becomes warm, hard, or tender.
Behavioral changes during the term
Some bitches become calmer, more social, or more restless. Others show almost no behavioral change. Appetite and activity levels may also vary.
Interest in other dogs increases, and the recall may become less reliable. This is hormonally related and will go away once the heat is over.
When symptoms should not be explained by the menstrual period
A bitch may behave differently during her heat, but obvious pain, pronounced lethargy, persistent vomiting or diarrhea, fever, or markedly reduced general condition should not automatically be explained by hormonal changes.
Contact your veterinarian if your dog seems ill, or has symptoms that are more pronounced than the usual changes around the time of the heat. Be especially careful in the weeks by period: increased thirst, lethargy, vomiting or abnormal discharge may be signs of uterine inflammation, which can be life-threatening.
Silent or irregular periods
Some bitches have a so-called silent heat, where the hormonal changes and ovulation occur without any obvious external signs. This means that she can become pregnant without the owner having seen any bleeding.
If a bitch does not have her first expected heat, the intervals change significantly, or she has prolonged or abnormal discharge, the veterinarian should assess whether there is a reproductive or hormonal disease.
Can maturity be postponed or prevented?
Hormonal drugs can in some cases be used to influence or postpone the period, but this is not a risk-free option. Such treatments can, among other things, affect the risk of uterine and udder disease, and should be assessed by a veterinarian.
In Norway, castration of healthy dogs is not routinely performed unless the conditions in the Animal Welfare Act Section 9 are met. The veterinarian assesses whether there is a medical or other special reason in the individual case. Read more about dog castration, and about the regulations at The Norwegian Food Safety Authority.
When should a veterinarian be contacted?
Contact us if you experience unexpectedly long or heavy bleeding, discharge outside of your cycle, missed first heat, a clearly changed interval, or if your bitch seems ill during or after the heat.
