Most intact female dogs follow a reasonably regular schedule for their heat cycles. (I know many of you are groaning, but the average female dog goes into heat at regular intervals, whether every four months or nine months or whatever.) If your dog has had a litter, her cycle may reset on a different time frame after having the puppies.
Most dogs start their heat cycles somewhere from 6 months of age to 2 years old. Toy breeds tend to come in heat when younger, while giant breeds when older. The dog’s breeder can tell you how her line runs and that often carries over. Most of my females have started with a first heat at about 13 months old and then have a heat every nine months.
Heat Cycles Are Not Periods
A dog’s heat cycle is different from a human “period.” Both involve bleeding, but for a dog, it signals a start to a fertility period whereas in humans it is the opposite.
As female dogs age, their heat cycles may get prolonged. A dog who normally had a heat every six months may now go nine or 12 months, potentially even longer. Also, heats may become less noticeable or intense in senior females. There may be less discharge, and she may not be as attractive to male dogs as when she was younger. These senior heats may mimic what is called a silent heat in younger dogs—no discharge and no obvious vulvar swelling—but the male dogs still show interest.
This is not the same as going into menopause like a senior woman, however. In aging people, the hormonal changes basically switch off the reproductive organs. This does not happen in dogs, so even an elderly bitch may become pregnant.
Bleeding From “Private Parts”
If your dog is bleeding from her vulva, carefully assess the situation. If she is not spayed, when was her last heat? Is there any evidence of trauma that might cause bleeding? Is her vulva swollen? Male dogs are often attracted to urine with blood, even if it is not part of a heat cycle.
Older female dogs are more likely to suffer from conditions such as bladder cancer or pyometra (a dangerous uterine infection). If she is spayed or not likely to be in heat, a veterinary visit is in order. A bladder infection or bladder crystals and stones are also possible. Uterine cancer, vaginal growths, or bladder cancer are all possible causes of a bloody discharge.
Dog Bladder Infections
If your female dog is urinating more frequently and doing extra licking even though she is not due to come in heat, the odds of a bladder infection are high. Ideally, you want to do a “free catch” urine sample first thing in the morning and take it to your veterinarian. Note: Walk your dog on a short leash and carry a saucer or small ladle you can quietly slip under her as she goes to pee. The sample should go into a clean container and be kept refrigerated until you can get it to the veterinary clinic, preferably the same day.
Although you very helpfully explained how canine heat cycles and human periods are not the same, and how dogs do not experience menopause, I’m surprised that you didn’t mention spay incontinence. Since some of the symptoms can be similar to a bladder infection, it would be helpful for owners of a spayed dog to know that the effects of the hormone disruption of spaying can cause this other urinary issue, even years later.