Changes in hormones, or the body’s signal molecules, are responsible for variations in your dog’s body and behavior during the heat cycle. Several female dog hormones work together, and their balance is what your dog’s body tell what to do.
If you want to understand the estrus cycle (commonly known as the dog heat cycle) in female dogs, a basic understanding of how those female dog hormones work is necessary. These are estrogen, progesterone, and luteinizing hormone. These may sound familiar as these are commonly known as sex hormones.
In this article, you’ll learn about the three most important hormones for your dog’s heat cycle, how they support pregnancy, and do dogs go through menopause.
Table of Contents
- What is Estrogen?
- Luteinizing Hormone and it’s role in the heat cycle
- Progesterone assists implantation and maintains pregnancy
- The Importance of Hormones in the Female Dog’s Body
- Hormonal Changes During Pregnancy
- Do dogs go through menopause?
What is Estrogen?
Estrogen is a steroid hormone primarily produced in the ovaries. It’s what your girl dog (also known as a bitch) needs for her sexual development, behavior, and it’s what makes her reproductive system work. During the first days of her heat, there is a significant rise of the estrogen hormone. As the name implies, it has something to do with the estrous cycle and one could say that it initiates it. For more detail on the 4 stages of the estrous cycle, please refer to our article which has much more information on What are the 4 stages of the dog heat cycle.
Humans also have estrogen just like all vertebrates do. Instead of estrogen, testosterone is what a male dog has also like us humans. As a side note, estrogen is actually a group of hormones of which the most known is estradiol. The list of estrogen’s functions is quite long; you can look it up at Wikipedia.
Estrogens are important in the sexual development of females. In regards to your dog’s heat cycle, estrogen promotes swelling of the vulva and creates the bloody vaginal discharge from the lining of the uterus to lubricate it. This is when you notice the red discharge, which is the first sign of a female dog in heat. Don’t worry. Your beloved four legged fur baby isn’t bleeding. The lubrication of uterine is essential for later implantation of a fertilized egg.
Your dog’s estrogen level continues to climb steadily, usually reaches its maximum two days before the beginning of the second phase of the heat (Estrus stage) and then decreases rapidly. The peaking of her estrogen level induces a sudden surge in another hormone, LH.
Luteinizing Hormone and it’s role in the heat cycle
The other hormone that regulates the heat cycle in female dogs (and not only dogs) is the luteinizing hormone (LH). The peaking of your dog’s estrogen level triggers the increase in production of LH. During the first days of the heat, the hormone stays at the base level but suddenly surges dramatically and drops back to slightly elevated levels within a day. This LH surge is what causes ovulation and not only in dogs, it does for us too.
Besides ovulation, the surge of LH also induces the production of corpus luteum or, a yellow body. This yellow body develops in the ovarian tissues in the ovaries after the egg leaves it. Its primary function is to promote and maintain pregnancy. It basically makes the uterus a nice place for a fetus to develop. It does this through a release of several hormones including estrogen that you already know and progesterone which you will learn about next. If you’d like to learn more about LH, you can learn more in Science Direct’s article on the Luteninizing Hormone.
Progesterone assists implantation and maintains pregnancy
Progesterone is another of female dog hormones. It is mostly produced by the yellow body corpus luteum. Your dog’s progesterone levels start to climb right after the above mentioned surge of the luteinizing hormone. Progesterone makes the lining of the uterus receptive for implantation and helps maintain the pregnancy.
If you are planning to breed your dog, measuring her progesterone levels can become invaluable. As said, her progesterone levels starts to climb right after the surge of luteinizing hormone. This means that when the progesterone starts to rise, you can predict that ovulation will occur within two days. More importantly, three days after ovulation is the most fertile time for dogs. This is critical information to understand to time the breeding or artificial insemination. When we mated our first Chocolate Labrador Retriever (male dog), the owner of the female didn’t measure her progesterone levels so we had to do 3 breeding sessions and artificial insemination just to make sure. We now know that if the owner had done that, we would have been known the ovulation timing and it would have been way less stressful on both dogs and us pet parents. For what ever reason, our male dog would come home exhausted and in desperate need of a bath.
However, progesterone levels are measured by blood tests. To catch the moment when it starts to climb, you should measure it daily (or according to your vet’s instructions) from the moment you first notice the signs of heat. Of course, the test has a price tag. Therefore, it is usually done when previous breedings have failed.
Progesterone level stays higher than usually about two months after the heat, regardless of whether the female dog got pregnant or not. Leutneizing hormone and estrogen, on the other hand, fall back to base levels well before the heat is over.
The Importance of Hormones in the Female Dog’s Body
Aside from their role in the estrous cycle, hormones play a vital role in the overall health and behavior of female dogs. Hormonal imbalances can cause a range of problems that can affect your dog’s quality of life and even shorten her lifespan.
Thyroid hormones for example, are responsible for regulating your dog’s metabolism. An imbalance can cause weight gain or loss, lethargy, or hyperactivity (similar to that in humans). In contrast, an excess of the cortisol hormone, known as Cushing’s disease, can lead to hair loss, skin problems, and an increased risk of infections.
Another more common hormone related problem is with spayed female dogs. They can develop urinary incontinence. While this usually occurs in spayed dogs, in can happen in a neutered male dog. Urinary incontinence is a hormone-responsive condition where the dog urinates normally but leaks urine when at rest. To learn more, you can read the University of Washington College of Veterinary Medicines article, Urinary incontinence in dogs.
It’s essential to monitor your female dog’s hormonal levels throughout her life, especially as she ages, to catch any imbalances early and address them promptly.
Hormonal Changes During Pregnancy
The hormones that regulate your female dog’s heat cycle continue to play a crucial role during pregnancy. As the fertilized egg implants into the uterus, progesterone helps to maintain the pregnancy and prevent the female dog from going back into heat.
During pregnancy, her estrogen level rises. This causes your bitch’s mammary glands to prepare for lactation. However, it’s essential to note that not all female dogs show physical signs of pregnancy until later stages. Thus, it’s best to have your veterinarian confirm a pregnancy to ensure proper care for the mother and her puppies. We recommend working with your veterinarian through the whole process. Before conception, we do a thorough exam to ensure she is happy and healthy. We continue to monitor her from insemination to the birth of those amazing little fur babies. Male dog owners also should have them checked fully for any genetic defects or other health issues which could potentially be passed on to the new puppies.
Do dogs go through menopause?
No. Unlike humans, female dogs don’t undergo menopause as they age. The ovaries can continue to produce eggs. She can still get pregnant and may cycle less as she ages. Unfortunately as she ages, hormonal imbalances can occur leading to changes in her behavior and health.
During this time, estrogen levels decrease, leading to a higher risk of urinary tract infections, incontinence, and weight gain. Female dogs may also experience behavioral changes such as increased aggression or restlessness. We recommend that our female dog patients be spayed once they are done breeding. Especially as the dog reaches the age of 8 years old as pregnancy at that age or above because she is more at risk of developing pyometra. This is a bacterial infection of her reproductive tract and can be life threatening. For more information on this, you can refer to the University of Illinois Champagne Urbana’s article Pyometra: Infection of Dog’s Uterus.
It’s important to monitor your dog’s health closely during menopause and make necessary adjustments to her diet and lifestyle to ensure she remains healthy and happy.
Hormones, including estrogen, progesterone, and luteinizing hormone play a critical role in your little girl’s heat cycle. Understanding how these hormones work and their importance in your dog’s overall health and behavior can help you care for your dog better.
Regular checkups with your veterinarian, including blood tests to monitor hormonal levels, can help detect any imbalances early and prevent health problems down the line.
You have learned about the three most important hormones for your dog’s heat cycle, how they support pregnancy, and do dogs go through menopause. This will go a long way towards a healthy and long happy life for your pet dog. And keeping your Pet Happy is what we all want.
If you are an owner of an intact female dog, you can find more information in our series about the heat cycle in female dogs: Dog Heat Cycle: A Comprehensive Guide for Pet Owners.