Although breeding and reproduction in dogs is not a passion of mine in veterinary medicine, I have managed to learn a lot over the years. When left to their own devices, dogs and cats typically don’t have too much trouble getting pregnant. Interestingly, however, when we try to control the process, it usually starts becoming more complex.
To be fair, I’m usually only involved when a breeding pair of dogs is not getting the job done. Either there are some “performance issues,” some “won’t get pregnant” issues, or some “this is probably not physically possible” issues, such as with some Bulldogs.
To be able to help effectively, you’ve got to learn about the female heat cycle, which is quite fascinating.
Remember that all of our dogs evolved from wild wolves. It may be pretty far back in the ancestry tree, but even your 6-pound Yorkie traces its forebearers back to Canis lupus.
I find the canine/wolf heat cycle so interesting because it is a biologic phenomenon that is influenced by genetics, environment, and social dynamics.
Let’s go to Yellowstone.
For much of the year, the hormonal status of female wolves is quite inactive. They are not going through monthly cycles like humans do. Then, in January and February, that changes. They will start their estrus cycle, which starts mating and breeding behavior. This is clearly influenced by the environment; there is something about the colder temperatures and the decreased sunlight that happens each winter that somehow triggers their ovaries to start waking up and producing estrogen. This is a really neat reminder for us humans that our natural health and wellbeing as a species is likely tied to a LOT of time spent outdoors. We often look at spending time outdoors as “recreation,” but perhaps paying attention to the other animals on this planet can remind us that we, too, can trace our roots back to earlier times when the outside environment played a much bigger part in who we are.
After a surge in some other hormones, the females will ovulate and become fertile. These same hormonal changes are also making them very receptive to mating.
Also fascinating is that wolves are very social creatures with some very instinctual “rules” that all the members of a pack play by. Namely, in a pack with several female wolves, only the alpha—the most dominant female wolf—is allowed to actually mate, despite the fact that all of the females are going through the same hormonal changes.
If the alpha female does indeed get bred and gets pregnant, it will take about two months for the pups to be born, compared to our 9-month gestation as humans. And so, every April and May, we are hopefully celebrating the birth of more wolf pups in Yellowstone, at a time of year when temps are warming up and food is relatively abundant.
Another fascinating thing about the female wolf cycle is that even the lowly female wolves who do not mate have the same pregnancy hormones rising in their bodies, just as if they were pregnant. After a few weeks of estrogen, the ovaries start making progesterone, which is the “hormone of pregnancy.” These non-pregnant dogs will start to develop mammary tissue and can even lactate. And indeed, if something goes wrong with Alpha Mom, there are some other females who are willing to step in and nurse to ensure the survival of the pups. Nature is amazing.
Our domestic dogs, even after we have tried our best to make them not-wolves, still follow a very similar cycle to their ancestors. Most of our domestic dogs will “go into heat” about twice a year, and as you might guess, the timing of this is not always so well-lined up with the seasons of the year. However, they all have a very similar hormonal story happening all through their cycle which makes figuring out the timing of when they need to be bred fairly easy to predict.
We will typically start to measure the female’s progesterone level after about 5 to 7 days of “signs of heat,” which typically includes some bloody discharge and swelling from the vaginal area. Once the progesterone levels start to rise, we know they are about to ovulate and can predict to the day when they should be bred and even when their due date will be.
However, just like with us humans, all the timing can work out perfectly and the male and female can be very healthy, but it simply doesn’t always work out. If you have any interest in breeding your dogs, you should come to the table with a lot of humility and patience and remember that we can never outsmart mother nature.
Of course, I can’t talk about this subject without giving a broad recommendation that everyone spay and neuter their dogs and adopt dogs from a shelter when possible. There are plenty of dogs out there, and did I mention that breeding dogs and doing all that progesterone testing is expensive? Also, if you want to breed your dogs, be sure to put away around $1,500-2,000, because you never know if your dog is going to be the one who needs a C-section at the emergency hospital, at midnight on a Saturday.
One more fact—the average survival of a wolf in the wild is only 3 to 5 years. So, dying this young, all of their reproductive organs are typically still healthy. The average age of our domestic dogs is more like 12-13 years, and if your dog is not spayed or neutered, it is extremely uncommon for them to make it to these ripe golden years without some major problems with their reproductive organs such as mammary cancer, uterine infections, and prostate infections and testicular cancer.
To the brave who will breed—good luck, and respect the cycle!