5 min read


Why Do Dogs Go In Heat



5 min read


Why Do Dogs Go In Heat




Your female dog seems to be licking her private parts and needing to urinate more often. She also seems a little more active, anxious, and flirtatious. You may have also noticed some bloody discharge. She is in heat and is ready to reproduce. All female dogs have a cycle, called estrus and it is perfectly normal. When a dog has her first cycle, the length between the cycles, the length of the cycle, and the age at which to breed or spay are all pretty standard though they can vary among breeds. It is important to know her signs and take care of her to avoid an unwanted or dangerous pregnancy. If you do not plan to breed your female dog, literally called a bitch, then plan to have her spayed as soon as possible as it can also decrease her chances of developing certain diseases.

The Root of the Behavior

A female dog can start her first cycle by as young as four to six months old and as late as two years old. It generally takes 18-24 months for it to become a bit more regular. Her cycle will last about one month and will come once or twice a year. The smaller the dog, the earlier her cycle will start and the more often she will go into heat in a year. The more giant breeds such as St. Bernard, Irish Wolf Hound, and Great Dane tend to have their estrus only once per year. Estrus begins with vulva discharge and when the vulva swells. She may also begin licking her vulva at this time. Blood in the discharge typically lasts the first two weeks, with her most fertile period being towards the end of the month. The discharge is not typically heavy or messy, though many female dog owners do purchase and use doggy sanitary napkins to protect furniture. Males tend to want to mate with a female dog in heat for an estimated 18 days though she may only be receptive to his advances for about nine of those days. Due to the shift in her hormones, she may appear alert, easily distracted, and at times nervous. She will flirt with males when she is ready to mate, by lifting her hind quarters up into his face, tense her backside, and flick her tail to one side or the other. She will urinate more often, and her urine is full of pheromones and hormones that signal to male dogs that she is in heat and will be ready to reproduce soon. If she is too young to mate, or you do not wish for her to mate but do not wish to spay her, it is important to keep her away from any males for the entire time she is in heat. Even dogs that are neutered will want to mate with her and it can cause stress and confusion for them. Experts recommend avoiding all dog parks, doggie daycares, and grooming salons while your dog is in heat. If you have a male dog in your home, it is also recommended to keep them separate as much as possible at this time. Nature is a strong force and coming between two dogs mating is not easy.

Need advice about your pet's health?

Get answers fast from a veterinary professional 24/7 in the Wag! App.

Get Vet Chat

Encouraging the Behavior

Prior to mating your dog, it is best practice to wait until she has passed through her third heat and has had genetic testing by your veterinarian to ensure she is ready. Most dogs are receptive to mating and have ovulated around the 11th day of their cycle. There are two tests you can perform to estimate the best time for her to mate, which are the serum progesterone test and vaginal smear test. The progesterone test measures progesterone levels and the vaginal smear tests analyzes cells over several days looking for changes that indicate fertility. Your dog will also tell you whether or not she is ready based on her reaction to your presenting her with a male dog. A male dog can reach mating maturity age by four to six months and will rarely turn down a female dog in heat. Male dogs tend to be the more sensitive of the two, so typically the female is brought to the male. They can mate once or twice over a twenty-four to forty-eight hour period.

Unless you plan on breeding your dog, it is recommended to spay her as soon as possible, ideally prior to her even starting her first heat cycle. Untying two dogs mating is nearly impossible, and a dog in heat has one thing on her mind so an accidental pregnancy is likely to occur unless you can be diligent about sequestering your female dog while she is in heat. If you rescue your dog after she has started her cycle, it is recommended to delay spaying her until she is at least eight weeks away from the end of her last cycle. Spaying requires removing the uterus. Because it is larger and more vascular when the dog is in heat, it is more difficult to remove and there is a greater chance of complications. Spaying your dog does more than eliminate the chance for an unwanted pregnancy. Dogs that are spayed have a decreased chance of mammary cancer and of developing pyometra, a possibly deadly infection of the uterus.

Other Solutions and Considerations

There are some instances when a dog may not have a heat cycle, some of which are normal and some that may need medical attention. Typically it takes about two years for a dog to develop a regular cycle, so anything that seems irregular prior to that may just be a part of her regular maturation process. After the two years, if she seems to miss a cycle she could have had a silent cycle, which is a real cycle without symptoms. Other reasons for a missing a cycle include malnutrition, hypothyroidism, ovarian hypoplasia, or a tumor on her ovaries. Your veterinarian can work with you, running a battery of tests to determine why your dog seems to be missing her cycle and speak with you about solutions.


All female dogs go into heat, or estrus, as part of their sexual maturity. Depending on size and breed, a female dog will begin her heat cycles anywhere from four months to two years of age, and she will have a cycle one to two times per year. Her estrus will last roughly four weeks, with her most fertile period being towards the end. If you do not wish for her to mate she needs to be kept away from male dogs for the entire cycle. If you do not plan to breed your dog it is highly recommended to spay her as soon as possible, but at least 8 weeks from her last heat cycle.

By a Black Lab lover Zoe Byer

Published: 02/20/2018, edited: 01/30/2020

What do you think?

Wag! Specialist
Does your pet have a supplement plan?

Learn more in the Wag! app

Five starsFive starsFive starsFive starsFive stars

43k+ reviews


© 2023 Wag Labs, Inc. All rights reserved.