The dog heat cycle, to many of us, is a bit of a mystery. They differ from the human cycle we know in many ways, but it is an important topic to understand if you have an intact female dog around.

The canine estrous cycle (aka heat cycle) consists of four phases. It takes an average of six months to complete the entire cycle, though this varies from dog to dog. A female dog will experience her first cycle when she reaches puberty, usually at 6 to 12 months of age.

Proestrus is the first phase where the body is preparing itself for mating, lasting 3 to 17 days. At this stage, the vulva will swell, and you may notice bloody discharge. Males will be attracted to females experiencing proestrus, but she will likely not be receptive to mating yet and may even respond to the advances with aggression.

The next phase is estrus. Many people refer to this phase as a dog being “in heat”, “in season” or “standing” because this is the mating phase where a female can get pregnant. This phase normally lasts anywhere from 3 to 18 days and you may notice that any swelling or blood flow seen in proestrus will decrease. In this phase, females ovulate, which is their most fertile time. She will attract males and if a male dog is near, she will likely present herself for mating at this time. Sometimes, females in this phase can be unpredictable. Some dogs will run away from home, others may become aggressive towards other dogs, while some might urinate in unusual places to spread their scent. It is important to get familiar with your dog’s hormonal behaviours and quirks to stay better prepared. Intact male’s behaviour is also affected when they sense a female in heat, they become very focused on mating and will do almost anything to get to a bitch in heat. Jumping fences, jumping through screen doors, digging their way into your yard and more are all things a male dog will do easily to get to a bitch in heat.

Following estrus is diestrus, lasting an average of 60 days (2 months). The body will either proceed with pregnancy or return to resting. At this stage, the swelling of the vulva and any discharge will have gone back to normal and disappeared.

The last phase is anestrus, being the phase with the least reproductive activity, in which no sexual or hormonal activity is present. It is the uterine repair phase, where the body rests and recovers from the previous phases or pregnancy. This phase lasts anywhere from 60-200 days, ending when proestrus begins again.

The only way to prevent a female dog from going through the estrous cycle is to have her spayed! Spaying your dog has many benefits, but if you choose to leave her intact, make sure you know the signs and patterns to look for, so you are aware of when your dog is in heat. Knowing when your dog is in heat is key in preventing unwanted pregnancies, planning for puppies if you do want them, avoiding dangerous situations, and being better prepared for the experience in general. If you have an intact male in the home as well, the chances of an unwanted and unplanned pregnancy increase dramatically. Even careful management and ‘crate and rotate’ often fail. Some handlers find it easiest to board their male dogs while their female is in heat so both dogs get a nice relaxing vacation.