Menopause is defined as the cessation of monthly cycles. Unlike humans, dogs do not go through menopause, as canines do not have a monthly cycle. Rather, they go into estrus (also known as heat) every six months or so. The regularity of their reproductive cycle depends on the age, breed, and individual dog
As a dog ages, the twice-annual estrus cycles may become irregular, but she is still fertile. Pregnancy is still a possibility, but with greater risk in an older dog.
For dogs that aren't spayed (uterus and ovaries removed is an ovariohysterectomy, removing the ovaries only is an oophorectomy), reproductive health risks increase. Here are potential problems to be aware of in unspayed female dogs.
Pregnancy Is a Risk
Pregnancy in a middle-aged or senior dog is considered a higher risk than in a younger dog, due to age-related conditions or diseases (known or subclinical) that may be present.
This condition, also known as pseudopregnancy or pseudocyesis. False pregnancy may occur at any age, regardless if she was mated or not. During a pseudopregnancy, the corpus luteum (the temporary ovarian structure that secretes progesterone after an egg is released, necessary to promote changes required to maintain a pregnancy) does not regress as it should.
With elevated levels of progesterone, the body and brain respond as if pregnant, resulting in signs seen that are common in late pregnancy: nesting behavior, territoriality, mothering behavior (collecting toys, etc.) as well as mammary gland development and milk production.
Most cases of mild pseudopregnancy resolve on their own in 2-3 weeks. Symptomatic treatment may be needed to reduce mammary discomfort and behavioral problems (anxiety) associated with this condition. If the dog will not be used for breeding purposes, spaying is recommended.
Pyometra is an accumulation of pus in the uterine cavity. It is caused by elevations in the hormone progesterone. As part of the normal estrus cycle or as part of a false pregnancy condition, progesterone levels rise, causing the uterine lining to be thick and "lush," ready for pregnancy. In the non-pregnant uterus, bacteria enter and cause the uterus to become filled with pus. The cervix may be open or closed, resulting in drainage from the vulva or not. Pyometra may be lethal if not treated. Medical therapy may be an option for some cases (never for closed pyometra), but the preferred treatment is to spay. Spaying also prevents pyometra development.
Similar to humans, mammary (breast) cancer is common in dogs who have not been spayed. Cancer may occur in any of the 8 mammary glands, or as multiple cancers in the mammary glands or associated lymph nodes.
When to See the Vet
The only way to stop the estrus cycles in the dog (without giving hormones) is to spay the dog (hysterectomy) or remove the ovaries (oophorectomy).
If your dog is lethargic, does not want to eat, and is drinking more water than usual, it is time to see your veterinarian. This is especially true for middle-aged to senior females who are not spayed, as pyometra would be one of the top medical conditions to rule out.