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Five signs your dog is in heat

How to know if your dog is in heat. A golden retriever being comforted
(Image credit: Getty)

How do you know if your dog is in heat? If you have an un-spayed female dog, they will tend to come into heat about once every seven months. However, just like in humans, individual patterns will vary. For instance, smaller breeds will tend to have their first season closer to six months of age than larger breed dogs.

Recognising the signs that your dog is in heat can be really important for breeding or for preventing breeding. If you’re intending to breed from your dog then the timings of potential matings with a stud dog will rely on accurate detection of the first signs of heat. If pregnancy is the last thing you want for your pooch, then you must spot the signs of heat so that you can take the necessary precautions to avoid accidental mating. But what should you be looking out for?

1. Swelling of the vulva

When a female dog is in heat their vulva becomes very large and swollen. It can become three or four times its original size but don't worry, it's not painful for her. This swelling can continue throughout the entire season of two to four weeks but should subside when your dog comes out of heat.

2. Discharge from the vulva

When your dog is in heat, they will develop a discharge from their vulva which changes over time. Initially, it may be straw-coloured or clear, but it will gradually become more bloody, and you will likely see spots of blood around the house, on the floor, on soft furnishings, or in your dog's bed

After about a week to ten days, the discharge will gradually become less bloody, returning to straw-coloured until the end of the season. If you notice a foul-smelling discharge soon after your dog's season, you should book an appointment with a vet urgently, as it could be a sign of a womb infection known as a pyometra.

A female boxer dog is in heat and licking her rear end

(Image credit: Getty)

3. Licking more around her back end

As a result of the vaginal discharge, you may notice your dog licking around her vulva a lot more to keep clean. This rarely causes any problem and is a good indication of heat, but if the licking is excessive watch out for signs of soreness or infection of the skin. If your dog continues to lick after a season, it could be a sign that there is still some discharge being produced. This could indicate infection, so make sure you contact your vet for advice.

4. Change in behaviour

The change you might see in behaviour when your dog is in heat is two-fold. Firstly, their interaction with other dogs, especially males, might change. She will likely become more receptive and interested in male dogs, and even if she normally gives other dogs the cold shoulder, she might tolerate them more during heat. 

Secondly, she may become more irritable, nervous, or aggressive whilst in season, even if she is normally quite confident. Therefore, it is important to be prepared for a change in her personality to avoid any bites or injuries. These changes in personality associated with coming into heat are usually temporary, and she should return to her normal self at the end of her heat.

5. Frequent urination

It is quite common for dogs who are in season to pass urine more often. This sign, combined with her licking at her vulva a lot, can understandably make a pet parent worry that there is a urine infection. However, these signs are a normal part of a dog’s heat and would only need investigating if your dog seems unwell or the symptom persists after the season has finished. 

So, how do I recognise that my dog is in heat?

If your dog is in heat, aside from showing more interest in male dogs, your dog will probably show some other characteristic signs. She will likely have a swollen vulva with a discharge that becomes pink or bloody. Because of the discharge, you may notice her cleaning or licking her vagina excessively and you might also notice that she passes urine more often than she normally would. She may be more fearful or grumpier than normal, so take care when around her and ensure she has a safe space to retreat to if she doesn't want to be bothered. 

Try not to fret if your dog is showing these signs, as they are normal for a dog in heat. However, if your dog is acting unwell during or after their season, it is important to get advice from a vet to make sure there is no infection of the womb, which can be very serious.

Dr. Hannah Godfrey BVetMed MRCVS

Dr Hannah Godfrey is a small animal vet with a love of dentistry and soft tissue surgery. She lives in Wales with her partner, son, and their two cats.