Heat in female dogs and cats

The complete anti-scare manual for guardians

One of the most disconcerting moments for many guardians is their pet’s first heat. Suddenly, your dog starts behaving unusually, becoming more restless, more dependent or even somewhat aggressive. Or your cat, who until recently slept peacefully, now won’t stop meowing, rubbing herself all over the house or trying to escape. What is happening?

These behaviours are neither coincidental nor a behavioural problem: they are natural manifestations of the oestrous cycle, a biological phase that prepares the female for reproduction. For decades, reproductive management relied almost exclusively on observation by the guardian or breeder. The modern leap forward came when clinical tools were developed that connect external signs with cellular and hormonal changes, greatly reducing errors in calculating the fertile period.

Recognising these signs is key to anticipating risky situations, such as unwanted mating, conflicts with other animals, or even escapes. In addition, correctly detecting oestrus allows you to make informed decisions about sterilisation, plan visits to the vet, and adjust the animal’s environment to reduce stress. In this article, I explain, in a clear and visual way, how to identify if your dog or cat is in heat and what changes you can expect to see during this period.

How to recognise when a dog is in heat (and why it is usually so obvious)

In female dogs, what we call ‘being in heat’ corresponds mainly to two consecutive phases of the cycle: a first stage in which the body prepares itself and becomes ‘visible’ to the outside world, and a second stage in which receptivity increases.

The “male magnet” has science behind it. In an experimental study on chemical communication in dogs, males showed a clearly greater interest in olfactory signals from females in oestrus when they could smell them up close, with behaviours such as prolonged sniffing and contact responses. This is good scientific support for explaining why, on walks, some males “lose their minds” when they detect a female in heat.

During the first few days, the predominance of oestrogen causes the vulval tissues to become more congested and the typical serosanguinous discharge to appear. In practice, the initial spotting usually lasts around 7 to 10 days, although some bitches spot very little and others spot quite a lot, without this in itself indicating a problem.

Here, a short list makes sense, because it summarises very well what helps the guardian to identify it without getting confused:

Vulvar swelling and spotting (more typical at the beginning).
Sudden attraction to males, even before the bitch is receptive.
Changes in social tolerance: some bitches become more sensitive, demanding or irritable with other dogs.
More frequent urination during walks, often as a form of marking.

As the cycle progresses, a hormonal event occurs that acts as a “trigger” for ovulation (the LH surge) and progesterone begins to rise around that time. This explains why it is not reliable to calculate fertility by simply counting days from the start of bleeding. As a clinical guideline, ovulation usually occurs 1–3 days after the onset of oestrus, but the individual range may vary.

In terms of duration, the receptive phase usually lasts an average of about 9 days, although there is considerable variability between bitches.

Your vet advises you 👩‍⚕️ (more developed)

If your bitch has light bleeding, do not assume that she is not in heat. There are cases of heat that are discreet in terms of bleeding but very “powerful” in attracting males and in changes in urination or social tolerance. In homes with real risk (e.g., living with an intact male), the best way to avoid surprises is not to guess based on the calendar, but to confirm the timing of the cycle with an examination and, if necessary, reproductive tests.

How to recognise heat in cats (when behaviour says it all)

In female cats, there is usually no visible bleeding, so identification depends almost entirely on behaviour. In addition, many female cats cycle more intensely when daylight hours increase; therefore, in homes with prolonged artificial lighting, some female cats may show signs of heat for more months of the year than the owner expects.

Here, too, a brief list provides real clarity, because these are signs that appear very consistently:

Intense and persistent vocalisation, sometimes especially at night.
Rubbing and rolling, with increased contact and attention-seeking behaviour.
Lordosis posture, raising the pelvis and deviating the tail.
Restlessness and attempts to escape, especially if she detects males nearby.

Clinical materials on feline reproduction explain that many typical behaviours associated with oestrus (vocalisation, lordosis, rolling, seeking contact) correlate with cytological changes in the vaginal mucosa. In other words, it is not the guardian’s imagination: there is a biological basis that can be confirmed – DVM360 – “Feline reproduction overview” (Proceedings) summarises clinical aspects of feline reproduction and includes the idea that typical behavioural signs of oestrus (vocalisation, lordosis, rolling, etc.) correlate with reproductive findings such as vaginal cytology.

Why does it seem to ‘come on suddenly’ in female cats?

Observations cited in the literature on feline reproduction have described that pro-oestrus (a more subtle preliminary phase) is detected in a minority of cycles, which helps to understand why many owners only notice oestrus, which is the most behaviourally striking stage.

In terms of duration, each episode of oestrus usually lasts several days (with averages around 7 days, although with wide ranges), and the complete cycle can vary from one to six weeks, with averages close to three weeks according to clinical references.

One biological detail explains many “loops”: female cats are typically induced ovulators, so ovulation is usually triggered after copulation. When there is no mating, it is common for them not to ovulate and to return to oestrus behaviour relatively quickly during the breeding season.

Common “around-heat” alterations that cause confusion (and how to interpret them)

In female dogs, the main source of confusion is pseudopregnancy. After oestrus, the body can maintain a hormonal pattern similar to that of actual pregnancy for a period of time. In this context, it is not uncommon to see behavioural changes that concern the owner: nesting behaviour, adopting toys as “puppies”, protecting objects, irritability and even reactivity. A veterinary survey on pseudopregnancy describes object mothering and nesting behaviour as very common, and many vets report having observed aggression associated with this condition, which fits with what is seen in consultations when owners describe their dog as “possessive” or “unrecognisable”.

In cats, the most common issue is not clinical pseudopregnancy, but rather the behavioural impact of repeated heat on cohabitation: family stress, lack of rest, and an increased risk of escape. In these cases, environmental management is often more useful than attempting to “correct” the behaviour as if it were a training issue.

When to seek advice without delay

This is one of the few areas where a list is really valuable, because it prevents a serious problem from being confused with heat:

Lethargy, fever, vomiting, abdominal pain, or a tense abdomen.
Foul-smelling, purulent, or persistent vaginal discharge out of context.
Noticeable excessive thirst and urination, especially if they appear after heat.
In female cats: signs of heat in a cat that has already been spayed (possible ovarian remnant or other causes), or abnormal behaviour accompanied by general signs.

Practical anti-scare tips for guardians

In female dogs, the number one risk during the period of maximum attraction is not that she will ‘misbehave’, but that an open door, carelessness with the leash or an insistent male will result in unwanted mating. The most effective approach is usually to reinforce simple measures: controlled walks, avoiding parks with loose dogs, and checking escape points if there is a garden or terrace.

For female cats, the priority is the safety of the environment. During heat, the motivation to escape can increase greatly, and here it is not the one who scolds the most who wins, but the one who puts up intelligent barriers. Well-secured mosquito nets, control of balconies and doors, and play routines to relieve restlessness often make the difference.