Female dogs, will generally go into heat during puberty, at around 6 to 24 months of age depending on breed. Smaller breeds generally come into heat earlier than larger breeds.
This can help you decide if it’s likely she’s in heat. For example, if she was in heat one month ago, it’s unlikely she’s in heat again so soon and something might be wrong. While most dogs come into heat twice a year, is every six months, as with any hormonal event some dogs are more regular than others. Some dogs come into heat as regular as clockwork every six months, whilst others are highly variable. A window of 4 - 8 months is considered normal. Dogs are usually in heat for three to four weeks.
This is also the week when she is most interested in finding a boyfriend, and so far from relaxing your vigilance, if you do not want the dog to have puppies you should tighten up on security. Around days 14 - 21 into the heat, the bloody discharge returns, but gradually lightens and dries up completely. However, the vulva often remains larger than normal for another couple of weeks (although she cannot get pregnant now her heat is over).
If a dog is scrupulously clean and licks away the discharge, it can be tricky to know if a discharge is present or not. A useful tip is to cover her bed with a white sheet or pillowcase. That way when she is asleep you will see blood spots on the white cover. If you plan on breeding your dog, write down the day that the bleeding begins. Breeding is best done on the 10th or 11th day after the first day of bleeding and then every other day after that for three days.
Some dogs will also bark more or become more aggressive with people and dogs around them.
However, dogs can mount legs or each other for behavioral reasons, such as masturbating, dominance, or bizarrely from submissive behavior, so this does not automatically mean a dog in heat.
You may also elicit this behavior by giving her a vigorous scratch on her rump. If she stiffens her back legs and diverts her tail to one side she is flagging. Never insert anything into the dog’s vulva or vagina to test out if she is ready. You can inadvertently cause harm to the delicate, inflamed tissues and cause huge distress to her.
The only way you can really confirm if a silent heater is in heat is by observing the interactions between male dogs and the female dog in question. Male dogs will detect even low levels of female reproductive hormones, which will arouse their intense interest and attention. Be aware that some dogs do “skip” a heat. If they are unwell or their health is below par, or if they have lost weight recently, their body may save its energy and she won’t come into heat when expected. This is nature’s way of saying her body needs all its reserves to look after number one, rather than being in a state of flourishing good health where she could care for puppies.
Although this is not foolproof and you need to interpret this in the context of the dog’s physical changes and the male dog’s usual behavior when kept apart from his female pal. Some dogs experience anxiety when separated from a close playmate and this is difficult to differentiate from sexual frustration.
However, allowing another dog to mount her, can also be a sign of submissive behavior, so once again, you need to interpret the whole picture and ask questions such as is her heat due and how does she normally behave around dogs. Remember, sniffing bottoms is something dogs like to do a lot, at the best of times, just to work out who is who! If your male and female dogs don’t normally interact, keep your male dog on a leash when you bring him near your female dog. One or both dogs may become aggressive if they are not familiar with each other.
The alternative is a test used in research establishments. It measures the level of Luteinizing hormone (LH) in the bloodstream, which rises prior to ovulation. However, this is not commercially available as a test kit.
A dog in heat has a typical pattern of large, cornified cells plus red blood cells that are typical of being in heat. This along with physical signs is enough to decide if the dog is in heat.
Is the dog due to be in heat? If yes, then heat is more likely than a health problem. Was she recently in heat? If yes, then another heat is unlikely and there may be a health problem. Is she in good spirits, eating and drinking normally, and normally active? If yes, heat is more likely. Is she not quite herself, is her appetite is reduced, is she more thirsty than usual, or does she keep vomiting? If yes, a health problem is likely and urgent veterinary attention sought.
If you have an older dog, who has recently been in heat (4 - 8 weeks before) and she develops a discharge, seek veterinary attention because this is the peak risk period for a pyometra developing. In the early stages the dog may be more thirsty or lack a good appetite. As the condition becomes more serious, the toxins causes kidney damage, and left untreated, can be fatal. Each time the dog has a heat it weakens the lining of the womb slightly and makes a pyometra more likely. This condition mainly affects aging dogs (the more cycles she has, the more likely it is to happen) and no breed is exempt from being at risk.
