How do I know if my
female dog is in heat?

What is “being in heat”?

Female dogs, or bitches (the proper word for a female dog, not an insult), come into heat approximately every six months starting around six months of age.  The proper term for this process is estrus, but most dog people just call it being “in heat.”  The only time a bitch can get pregnant is when she is in heat.  However, a bitch is in heat for 21-28 days each time she come into heat.  Physiological changes due to hormone fluctuations can cause a dog to be cranky and disagreeable during this time, as well.

Dogs do not adhere to strict timelines when it comes to estrus.  The times given are approximate.  Every dog has her own cycle.  Big dogs tend to be older when they first come into heat and may have more time between heats.

Stages of estrus

Proestrus is the first stage of heat.  It is the stage where the dog begins vaginally bleeding and is when the owner first notices something is going on.  Male dogs will become very interested in the bitch and may begin fighting over her.  Other bitches may become aggressive toward her and she may be aggressive back.  This generally lasts nine days and the bitch is not considered fertile at this time, but may mate.

Estrus is the time when the bitch is fertile and may get pregnant.  She goes from wanting to rip the face off any male that approaches to standing and moving her tail out of the way for him.  This is called “flagging” and is considered a sign the bitch is fertile.  However, some females never flag and some always do, so it is not totally reliable.  The vaginal discharge lessons in this stage and turns more straw colored.  This stage lasts four to seven days.  There are tests the veterinarian can administer that will detect when the best time to breed the bitch is during this stage.

Metestrus is the last stage.  The body of the bitch readies itself for pregnancy, even if she has not mated.  Dogs are still attracted but the bitch does not want to mate.  In about 14 days, the bitch may display signs of pregnancy even if she is not pregnant.  This is called false pregnancy and can signal a problem.  A veterinarian can advise you as to whether it is a true or false pregnancy and what needs to be done about any problems.

Anestrus is the resting stage between heats.  It generally lasts about five to six months.

Problems associated with estrus

Some people think a dog should be allowed to come into heat one time, or even have a litter, before being spayed.  This is not true.  If the dog is spayed before her first heat, she will not get ovarian, uterine, or cervical cancer and is virtually immune from breast cancer as well.  If your dog is not a champion show, obedience, or working dog, consider spaying her before her first heat.

If your dog comes into heat, she must be segregated or she will mate with whatever male is available.  When that happens, the male’s penis swells and locks into the female’s body.  Pulling apart these dogs while they are “tied” can lead to severe internal injuries for the female and injuries to the genitals of the male.  Ties typically last about twenty minutes, but can last as long as an hour.  Bitches can panic, and struggle, so may need to be held still during this tie to prevent them from injuring themselves.

A litter can have multiple fathers.  Each time the bitch mates during estrus, eggs can be fertilized and the puppies can join the litter.  DNA tests can separate which puppies have which father, and the American Kennel Club will accept those results and register the litter.

One very serious complication of estrus is pyometra.  This is an infection of the ovaries that can kill a bitch.  The ovarian horn fills with puss and can burst; causing a general infection that is fatal.  Generally, the dog must be spayed when pyometra strikes.  If you see a discharge that looks like puss, get your dog to a veterinarian immediately.  This is an emergency.

False pregnancy is also a problem.  The dog does not become pregnant, but her body and her mind believe she is pregnant.  She may carry around a toy and treat it like a puppy for a long period of time.  Dogs that have false pregnancies are more prone to pyometra, so watch them closely.


Brucellosis is a disease that causes abortions of the poppies in the bitch and can kill the bitch.  It is sexually transmitted.  If you bred your bitch insist that both dogs be cleared by a simple blood test administered by your veterinarian.

In closing, the estrus, or heat cycle, is traumatic for dog and owner.  The best thing for both is to spay the dog before she is ever in heat.  If you have a dog that is a champion and will significantly add to the breed, then you will need to work closely with your veterinarian to successfully breed her.

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"Heaven goes by favour. If it went by merit, you would stay out and your dog would go in." -- Mark Twain