March 10, 2026, 5:38 am | Read time: 6 minutes
Your female dog is almost two years old, but she still hasn’t gone into heat? Maybe that’s why you’re worried. Female dogs should be going into heat at this age, shouldn’t they? PETBOOK asked a veterinarian if this is a cause for concern.
How Often Do Female Dogs Go Into Heat Each Year?
How long is a “normal cycle” anyway? It’s hard to say exactly, says veterinarian Dr. Joachim Hölter from Stade. “The time between two heat cycles can be as short as five months or as long as twelve months—both are within the normal range,” says the doctor. Small dogs generally have shorter cycles than large breeds, so the cycle duration should always be assessed individually, and there’s no such thing as “normal” at first.
The duration doesn’t remain the same throughout life, as the veterinarian reveals. “Even in female dogs with a regular cycle, the time between two heat cycles can vary by more than a month without it being a cause for concern,” says Hölter. As they age, from about seven to ten years, the time between heat cycles can further extend, or the heat cycle may even stop altogether.
When Is It Considered a Delayed Cycle (Anestrus)?
The interval between two heat cycles in most female dogs is between five and twelve months, averaging about seven months. A delayed or absent cycle is considered when:
- The female dog is older than 18–24 months and has never been in heat (primary anestrus).
- More than 12–18 months have passed between two heat cycles (secondary anestrus).
The causes for a missing cycle are varied and include endocrine (hormonal), nutritional, environmental, and genetic factors. “There are many causes for a pathologically prolonged cycle interval, such as ovarian cysts or hormonal disorders like hypothyroidism or Cushing’s syndrome,” says veterinarian Dr. Hölter.
The Main Causes for the Absence of Heat Cycles
The reasons why a female dog’s heat cycle is absent can be divided into four main areas.
1. Age and breed-related factors
It doesn’t always have to be a disease. Especially in young animals, the normal range of first heat for the breed should be considered.
- Delayed puberty (breed/size): As mentioned above, large and giant breeds (such as Great Danes, Newfoundlands) have a significantly longer juvenile phase and often go into heat for the first time at 18 to 24 months.
- Seasonal cycles: Although female dogs do not go into heat strictly seasonally, environmental influences or contact with intact males can subtly affect the cycle.
2. Hormonal and endocrine disorders
The heat cycle is primarily controlled by the hormones estrogen and progesterone, as well as pituitary hormones (FSH and LH). An imbalance in this axis is a common cause.
- Hypothyroidism: A reduced function of the thyroid gland can slow down the entire metabolism and negatively affect the reproductive cycle. In such cases, the heat cycle either does not start at all or the cycle is drastically prolonged.
- Pituitary disorders: The pituitary gland controls the maturation of eggs and the production of sex hormones through the release of LH and FSH. Dysfunction can block the cycle.
- Ovarian cysts/tumors: Diseases of the ovaries can disrupt or prevent normal hormone production, preventing the heat cycle from being correctly triggered.
- Persistent corpus luteum: If the corpus luteum, which produces progesterone after ovulation, remains active beyond the normal duration (which is rare but can occur), it can prevent the onset of a new cycle.
3. General medical and nutritional factors
The entire organism must be in a healthy state for reproductive processes to occur.
- Malnutrition/underweight: Severe underweight or malnutrition (especially of essential fats and nutrients) signals the body that resources for pregnancy are insufficient. Nature instinctively prevents the onset of the cycle in such cases.
- Chronic diseases: Severe systemic diseases (such as kidney failure or diabetes) can burden the body so much that the cycle is suppressed.
- Stress and environmental changes: Extreme stress (such as moving, new pets, the death of the owner) can temporarily lead to a cycle shift, but is rarely the sole cause of an anestrus lasting many months.
4. Anatomical and genetic causes
In rarer cases, congenital or acquired physical problems can prevent the heat cycle.
- Intersexuality (pseudohermaphroditism): This is a genetic anomaly where the female dog appears outwardly female, but the internal sex organs are not fully or correctly developed, disrupting hormone production.
- Undetected spaying: For female dogs adopted from second-hand or rescue situations, it must always be clarified whether a spaying may have been performed that is not documented.
- “Silent heat” (subestrus): The female dog was actually in heat, but the external symptoms (swelling, bleeding) were so weakly pronounced that they were overlooked by the owner. This is a regular “cause” for secondary anestrus. The female dog is then in the resting phase without it being noticed.
Hair Loss in Dogs: What Owners Need to Know
Hormone Chip for Contraception in Dogs? What Experts Advise
When to See a Veterinarian
An absent heat cycle is not always a cause for concern, but it should not be ignored. “If a female dog does not go into heat as expected and shows disturbed general well-being, such as reduced appetite, increased drinking, lethargy, or vomiting, she should be examined by a veterinarian,” says veterinarian Dr. Hölter.
In the case of pyometra, purulent or bloody vaginal discharge may also occur. The disease is quite common and is considered the most common gynecological disease in female dogs, affecting every third to fourth intact female dog. “The disease usually occurs in middle-aged to older female dogs,” says veterinarian Dr. Hölter.
Conclusion
The absence of a heat cycle can have many causes—from completely harmless breed-specific characteristics to hormonal or anatomical problems. It is important to observe your female dog closely and take changes seriously without worrying prematurely. Especially in large or late-maturing breeds, a first heat beyond 18 months is not unusual.
If your female dog has never been in heat by the age of over two years or if the interval to the last heat cycle becomes significantly longer than usual, you should seek veterinary advice. Modern diagnostics, such as hormone profiles, ultrasound, or vaginal cytology, allow your veterinarian to reliably narrow down the cause and treat it if necessary.
The most important thing is to establish clarity early on. This way, you can ensure that your female dog remains healthy and any disturbances in her reproductive cycle are detected in time.