By Jennifer Coates, DVM
Women have a distinct time period during our lives when it is possible to have children. We begin our monthly menstrual cycles as puberty hits, but at some point they stop. Menopause signals the end of our child-bearing years. It’s natural to wonder if dogs experience something similar.
Some aspects of the human and canine reproductive cycles are similar. Females of both species experience regular fluctuations in their hormones, but the timing, duration, and effects of these changes are very different. We’ll focus on estrogen and progesterone, even though there are several other hormones that play important roles.
A woman’s monthly hormonal cycle goes something like this:
Week 1: Her period has just ended and estrogen and progesterone levels are low.
Week 2: Estrogen levels are increasing in preparation for ovulation.
Week 3: Progesterone levels are increasing in preparation for pregnancy.
Week 4: If pregnancy has not occurred, both estrogen and progesterone levels drop.
Dogs do not go through a monthly menstrual cycle. Instead, they go into “heat” every four to 12 months or so. Assuming a six- to seven-month cycle, this is what a dog’s hormonal fluctuations look like:
Months 1-4: Low estrogen and progesterone levels. No reproductive activity.
Week A (may last days or weeks): Estrogen levels are increasing in preparation for ovulation. The dog’s vulva is swollen and a bloody discharge is present.
Week B (may last days or weeks): Estrogen levels are decreasing. Ovulation has occurred. The dog is willing to mate. The vulva remains swollen but discharge may decrease. Progesterone levels are increasing in preparation for pregnancy.
Months 5 and 6: Estrogen levels are low. Progesterone levels are high to maintain a pregnancy. The dog may experience a false pregnancy even if mating did not occur since her hormones are the same regardless.
When a woman experiences menopause, her monthly cycles stop and her body produces very low levels of estrogen and progesterone for the rest of her life. This does not occur in dogs. Healthy female dogs will continue going into heat on a regular basis throughout their entire lives. Reputable reports exist of dogs as old as 16 becoming pregnant. This is equivalent to an 80- or 90-year-old woman!
Changes in Pregnancies and Heat Cycles with Age
This is not to say that dogs typically retain high levels of fertility to such an advanced age. Usually around age 5 or 6, they will begin to become less able to maintain healthy pregnancies. This may occur sooner in larger breeds and later in smaller breeds due to the differences in their aging rates and life expectancies. A dog’s overall health status can also play a role.
One study in laboratory beagles used for breeding showed a dramatic rise in the death of newborn puppies with the increasing age of the mother. By age 9, around 80 percent of the puppies died before weaning. The situation may not be exactly the same for pet dogs, but the trend probably remains similar. The incidence of serious problems for the mother, like a difficult birthing process or low blood sugar and calcium levels, also appears to be higher with increased age.
Even though female dogs are supposed to continue cycling throughout their lives, it sometimes appears as if their heats have stopped or become irregular. Some dogs will experience “silent” heats. The typical signs (vulvar swelling and the presence of a bloody discharge) may be minimal or simply not observed. Some dogs naturally have an extremely long period between their heats—up to 13 or 14 months can be normal. But when an older dog truly stops cycling, a health problem is probably to blame. For example, ovarian cysts or ovarian cancer can disrupt a dog’s hormonal production and prevent the expression of a normal heat cycle.
Benefits of Spaying
Does nonstop cycling have a detrimental effect on a dog’s body? Yes! In essence, dogs are “built” to become pregnant with every heat. They experience a “hormonal” pregnancy (two months of high progesterone and low estrogen levels) after every heat regardless of whether or not they have mated. This puts them at high risk for developing a potentially fatal uterine infection called pyometra after each heat, and this risk increases with advancing age.
The risk of mammary (breast) cancer is also very high in older, intact females. Spaying a dog before her first heat provides virtually complete protection against mammary cancer throughout her life. Other benefits of spaying include eliminating messy heat cycles, unwanted pregnancies, and the risk of ovarian and uterine diseases (cancer, benign tumors, infections, cysts, etc.).
Of course, spaying is not without potential downsides, including an increased incidence of incontinence and some types of orthopedic disease and cancer. It can be difficult to assess all of the risks and benefits associated with spaying, but a big study looked at the bottom line (life expectancy) and found that, on average, dogs who were spayed lived longer than those who were not. A veterinarian familiar with an individual dog’s situation is in the best position to recommend whether or not (and when) she should be spayed.
Do Dogs Experience Menopause-like Symptoms After Spaying?
Many of the symptoms women experience around the time of menopause are related to declining levels of estrogen and progesterone. Since spaying results in a similar situation for dogs, the question of whether they experience something akin to menopause can arise. The truth is, we simply don’t know. However, since most dogs are spayed when their estrogen and progesterone levels are already quite low—before puberty or when they are not in heat—and they normally go through months when their bodies produce few reproductive hormones, it seems unlikely that they would be troubled by hot flashes, mood swings, or other symptoms commonly associated with menopause.