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Golden Retriever laying in the grass

A female dog reaches sexual maturity at around six months old. The stage of the cycle when she’s receptive to mating is called estrus, or heat. During this stage, there’s an increase in estrogen levels, then a sharp decrease and then her ovaries release eggs. Although six months old is the average age of a dog’s first heat, this can vary widely. Some dogs can go into heat as young as four months, while larger breeds may be as old as two years before their first heat. Responsible breeders never breed a dog on her first or even her second heat. It is considered best practice to wait until her third heat, at about 18-24 months. Your vet will perform any necessary genetic testing and will also be able to tell you when your dog is ready.

How can you tell if your dog is in heat?

There are distinct signs of estrus, both physical and behavioral. She may urinate more than usual. There will also be a blood-tinged discharge and swollen vulva. She may seem nervous or distracted. She’ll be receptive to male dogs and may initiate sexual contact, including raising her rear towards male dogs and deflecting her tail to one side, which is called ‘flagging.’ During the middle stages of the cycle, a female dog will actively court males and this may continue until the cycle is over.

How often will my dog go into heat?

Female dogs cycle into heat on average every six months. But this can vary, especially in the beginning, so it’s a good idea to keep track. It can take some dogs 18-24 months to develop regular cycles. Small dogs will tend to go into heat more frequently, as much as three or four times a year. Very large breeds, like Great Danes and St. Bernards among others, may only go into heat every twelve months.

The estrus cycle usually lasts an average of three weeks, although this can vary from 2-4 weeks. It begins with swelling of the vulva and vaginal discharge and ends when all bleeding has stopped. A female may allow a male to mount her at any time during the cycle, although most not only only accept mounting later in the cycle, but actively seek it.

Your dog will continue to go into heat throughout her life, although the length of time between estrus will increase as she gets older. With experience, pet owners become more adept at recognizing the onset and taking good care of their dogs during this natural life cycle.
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