Oestrus

Oestrus is the fertile phase in a female dog’s reproductive cycle, during which she is ready to mate and can become pregnant.

In Switzerland, this means for dog owners: approximately every six to twelve months, the female dog’s behaviour changes noticeably. She is courted by male dogs, shows bloody discharge and can become pregnant if mated unintentionally. The oestrus cycle comprises several phases with different symptoms and lasts two to four weeks in total.

How does the oestrus cycle work in female dogs?

The cycle consists of four consecutive phases:

Prooestrus (7-10 days): The vulva swells, bloody discharge begins. The female dog attracts male dogs but does not yet allow mating. Oestrogen levels rise.

Oestrus (5-9 days): The actual oestrus phase. The discharge becomes lighter and more watery. The female dog stands for male dogs, meaning she lifts her tail to the side and allows mating. Ovulation occurs during this time.

Metoestrus (60-90 days): Progesterone levels remain high, regardless of whether the female dog is pregnant or not. This is why pseudopregnancies can occur.

Anoestrus (4-5 months): The resting phase. No signs of fertility, the body prepares for the next cycle.

When do female dogs come into heat for the first time?

The first oestrus occurs between the sixth and twelfth month of life. Small breeds such as Yorkshire Terriers or Chihuahuas often come into heat as early as six months. Large breeds such as Great Danes or Bernese Mountain Dogs take longer, sometimes until the 18th month.

After the first heat, the cycle repeats every six to twelve months. Most female dogs come into heat twice a year, but individual variations are normal.

What are the typical signs of oestrus?

Bloody vaginal discharge is usually the first visible sign. Many owners notice it because the female dog suddenly leaves traces on carpets or resting places.

The vulva swells noticeably, in some female dogs so much that sitting becomes uncomfortable. At the same time, the female dog begins to mark more frequently. What is normal for male dogs is shown by females in heat as a signal of their fertility.

Behavioural changes are very individual. Some female dogs become more affectionate and seek more physical contact. Others react unusually irritably or restlessly. From the oestrus phase, the female dog shows the typical “standing reflex” when touched on the hindquarters; she presses her hindquarters upwards and lays her tail to the side.

How do I prevent an unwanted pregnancy?

During the fertile phase, the female dog must be kept separate from male dogs. This means: leash requirement, no off-leash runs in dog parks and attention when walking. Male dogs can smell a female in heat over kilometres and will pursue her persistently.

Ovariohysterectomy is the only reliable long-term solution. The ovaries (and usually the uterus) are removed. The oestrus cycle ends permanently.

Hormonal contraception by injection or tablets is possible but controversial. Side effects can be serious, from uterine inflammation to diabetes. Reputable vets usually advise ovariohysterectomy rather than hormonal suppression.

What happens in a pseudopregnancy?

About six to eight weeks after coming into heat, female dogs can develop a pseudopregnancy, even without mating. The reason lies in the particular hormonal situation: progesterone levels remain high for weeks after oestrus, as if the female dog were actually pregnant.

Typical signs are milk production, nest-building behaviour and “adopting” toys as replacement puppies. Some female dogs become particularly affectionate at this time or protect their “nest” aggressively.

In most cases, the symptoms disappear on their own after two to three weeks. In cases of heavy milk production or pronounced behavioural changes, the vet can provide supportive treatment.