Older, intact female dogs -- those who haven't been spayed -- don't experience menopause in the way aging women do, but their fertility decreases as they age. Although dogs do bleed during part of their heat cycle, they don't experience periods every month as women do. The only true sign of "menopause" in a female dog is less frequent estrus cycles. That generally starts about age 7.
Canine Estrus Cycles
A dog's estrus, or heat, cycle lasts between two and three weeks, and is divided into three phases. Proestrus, the first phase, is the time when the dog experiences bleeding. The second, or estrus, phase is when ovulation occurs and the dog can become pregnant. The third phase, diestrus, occurs whether or not the dog is pregnant, as far as her hormones are concerned.
Most dogs experience their initial estrus cycle around the age of 6 months, although it is often later in large breeds. For the next few years, unless spayed, the dog will go through estrus approximately twice a year, although some breeds only cycle annually and smaller breeds might cycle three times a year. As the dog ages, her cycle becomes more erratic, but they don't completely stop as they do in human females.
If an older dog conceives, she's likely to produce a much smaller litter than a younger animal, or as many puppies as she had in her youth. After age 5, most dog breeds produce fewer puppies per litter, according to the American Kennel Club. Small breeds are an exception, but small breed dogs produce fewer puppies per litter -- often significantly so -- than medium or large breeds. Other signs of decreased fertility include lower conception rates and more frequent puppy deaths in litters.
Pyometra in Older Dogs
If you have an older, intact female and have no intention of breeding her, consider having her spayed. While it's major surgery, most older dogs in good health recover well. Spaying prevents pyometra, a potentially fatal uterine infection most often occurring in aged female dogs. Older dogs who have gone through many heat cycles without pregnancy are most vulnerable, as changes in the uterine wall allow bacteria to thrive.
Signs of pyometra include pus emanating from the vulva, along with possible fever and lethargy. As gross as seeing pus come out of your dog's genitals may be, the prognosis is far worse if a closed cervix doesn't allow infected material out. Closed pyometra rapidly develops into a life-threatening condition, requiring emergency surgery to save the dog's life. Animals suffering from closed pyometra are obviously very ill.