Like humans, dogs have a reproductive hormone called progesterone that fluctuates when they’re ovulating. Progesterone testing is a blood test used to determine when a dog is ovulating and, therefore, ready to breed. Assuming the dam and sire are healthy, ovulation mistiming is the most common reason a dog fails to become pregnant.
Key Points
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Although nothing is guaranteed, progesterone testing is a helpful tool for predicting when a dog is ovulating and ready to breed. The best time to breed depends on a combination of factors including progesterone testing, monitoring a bitch’s signals, and working with a veterinarian who specializes in canine reproduction. “It might be useful to have progesterone levels tested on a heat cycle even if no breeding is planned, just to have an idea of how a bitch behaves at any given level,” Dr. Wiley says. The results aren’t always consistent from one cycle to another, but it might help when planning future litters.
Since a lot goes into planning a litter, it’s important to understand how ovulation timing works. Read on to learn about the canine reproductive cycle, including signs of estrus (i.e., when a dog is receptive to mating), progesterone testing methods, breeding timing, and reproductive function testing.
What Are the Phases of the Canine Reproductive Cycle?
Before delving into progesterone testing in dogs, it helps to be familiar with the canine reproductive cycle. Being “in heat” means that a dog is receptive to mating and can become pregnant. When female dogs are two-thirds of their adult size, they can have their first heat cycle, also referred to as estrus, says Dr. Kelly Hood, DVM, in-house veterinary expert at Pet Portraits and consultant for California Dog Kitchen. “This can range anywhere from 6 to 18 months depending on the breed of dog,” she adds.
Larger breeds take longer to come into heat. Typically, unspayed dogs have two heat cycles a year, each lasting approximately 2 to 3 weeks. “Just like with humans, a dog’s cycle is variable,” she says. The interval between estrus cycles could be six months or longer. Dogs can become pregnant during their first or subsequent heat cycle.
There are four phases of a female dog’s reproductive cycle: proestrus, estrus, diestrus, and anestrus. “Proestrus and estrus comprise a dog’s heat cycle and are characterized by a decrease in estrogen and a rise in progesterone,” she says. Estrogen is involved in the maturation and release of eggs.
Signs a Female Dog Is in Heat
During proestrus, the vulva becomes swollen accompanied by bloody discharge. “Proestrus could be considered the dog’s period, lasting 10 to 14 days on average, and can sometimes be subtle,” she explains. Dogs aren’t fertile yet and don’t allow mounting.
In the second phase, female dogs are in heat and are receptive to males. “This is when there is a spike in luteinizing hormone which causes the ovaries to release the eggs,” she says. Ovulation occurs in this phase, meaning dogs can be bred, and the eggs can be fertilized. Estrus lasts 5 to 10 days and is marked by the following changes.
Physical signs of estrus include:
- Swelling of the vulva or external genitalia
- Vulva has a golden or straw-like color
- Bloody vaginal discharge without clots
- Frequent urination especially in the presence of a male dog
Behavioral signs of estrus include:
- Playful behavior with male dogs but not yet receptive to breeding
- Releasing pheromones, vocalizing, or arching their body
- Increased physical activity
- Nervous or fidgety
- Acting clingy
- Mounting or humping other dogs
What Is Progesterone Testing?
Progesterone testing is “a blood test that can be helpful in predicting when the dog will ovulate and be the most successful in getting pregnant,” Dr. Hood says. Prior to ovulation, the level of progesterone increases in the bloodstream. When this happens, the pituitary gland, located at the base of the brain, secretes luteinizing hormone which triggers the release of eggs from the ovaries.
A dog is thought to be ovulating when the progesterone level reaches 5 to 10 nanograms (a measure of one billionth of a gram) per milliliter of blood, says Dr. Jerry Klein, DVM, Chief Veterinarian for the American Kennel Club. He explains that, in breeding dogs, ovulation timing is extremely important and often the most common thing that can go wrong. Some dogs reach the ideal progesterone level sooner than others, adds Dr. Claire A. Wiley, VMD, DACVIM.
When Is Progesterone Testing Done?
- “The first progesterone sample should be drawn 7 to 10 days after the first signs of proestrus to get a baseline,” Dr. Hood says. “Once the luteinizing hormone begins to rise, so will the progesterone levels.” Signs of proestrus include vulval swelling and discharge. She recommends taking another sample two to three days later, taking note of when there is a steady rise in progesterone. Dr. Wiley agrees, adding that progesterone should be tested every other day once the level increases.Making several trips to the veterinarian may be inconvenient, but the knowledge gained is worth it. “Knowing when a bitch ovulates as detected by progesterone testing significantly increases the chance of a successful breeding,” Dr. Klein says. “Progesterone testing also helps to determine a bitch’s due date.” This is especially important if the bitch is close to term, or you’re planning a C-section since, unlike humans, dogs don’t have a two-week window for a safe delivery.
Progesterone Testing Methods
“The gold standard for progesterone testing is radioimmunoassay (RIA) testing,” Dr. Klein says. This test detects the level of progesterone in the blood. Usually, RIA testing is only available in veterinary teaching hospitals or large reference laboratories.
“Some veterinary hospitals have a progesterone test that produces results in one hour based on chemiluminescence,” he says. This test involves light being emitted from a chemical reaction. Another option is at-home testing kits which estimate the level of progesterone through color changes. However, these tests aren’t as accurate as chemiluminescence or RIA progesterone testing, he adds.
“Alternatively, these changes in cycles and hormone levels can also be determined by vaginal cytology,” Dr. Hood says. “Vaginal cytology is a practical and inexpensive way to determine the types of cells present in a bitch’s vaginal wall at a particular time,” Dr. Klein adds. This procedure involves collecting cells from the vaginal wall with a cotton swab and examining them under a microscope.
Vaginal cytology can help determine which phase of a heat cycle a dog is in and the best time to breed. A single smear can be misleading since it may pick up on other problems like vaginitis (inflammation of the vagina). Therefore, “it is most useful to evaluate multiple smears taken from the same bitch during her cycle,” he says.
Determining if a Dog Is Spayed or Neutered vs. Intact
While physical signs may provide clues, certain diagnostic tests may be helpful or necessary when seeking to understand whether a dog has been spayed or neutered.
Ovarian Remnant Syndrome
Since spaying involves the removal of a dog’s ovaries, you wouldn’t expect these dogs to display signs of a heat cycle. Ovarian remnant syndrome is a disorder that results from a failure to remove some or all of an ovary during surgery. When ovarian tissue remains, these dogs, despite being spayed, may show signs of coming into heat.
Testing for this disorder “consists of Anti-Müllerian Hormone (AMH) and progesterone testing on a single blood sample,” Dr. Klein says. “A positive AMH test is consistent with the presence of an ovarian remnant, but a negative AMH test does not rule out the presence of an ovarian remnant.” In dogs, the corpora lutea are a collection of cells that produce progesterone but not AMH.
“If a sample is collected after ovulation, a high progesterone level with an inconclusive or negative AMH result could be diagnostic for an ovarian remnant,” he says. “So, the progesterone level is especially important when the AMH is negative.” Because treatment of this disorder involves invasive surgery, the veterinarian will want to rule out other sources of progesterone besides residual ovarian tissue.
Cryptorchidism (Retained Testicles)
Unlike females, male dogs don’t have a heat cycle. Their fertility peaks when they are fully mature. Males are receptive to female dogs in heat any time of year.
Cryptorchidism refers to when one or both testicles fail to descend into the scrotum. Cryptorchid dogs may be infertile and should not be bred. These dogs “typically have higher testosterone levels compared to a neutered dog, allowing a veterinarian to differentiate between the two conditions through a blood test” Dr. Klein says. He explains that a single testosterone test might not give you a definitive diagnosis of cryptorchidism.
The veterinarian may need to conduct further tests like “an ultrasound or a stimulation test with human chorionic gonadotropin (hCG) for a conclusive diagnosis,” he says. “For hCG testing, two blood samples are performed, an initial blood draw followed by a second draw 12 to 24 hours post-injection.” An increase of two to four in the testosterone level from the baseline suggests the dog has retained one or both testicles.
When Is It Time to Breed?
“Before trying to breed, ensure that the female dog is up-to-date on vaccines and parasite control,” Dr. Hood says. When the progesterone level is 5 to 10 nanograms per milliliter, this is a good time for breeding using fresh semen, naturally or by vaginal artificial insemination, Dr. Wiley says. Fresh, healthy semen can survive in the bitch’s reproductive tract until the eggs mature.
Breeding using fresh chilled or frozen semen should take place when the progesterone level is 20 nanograms per milliliter, Dr. Klein says. “The prime time to breed in dogs is 48 to 72 hours post-ovulation because, after ovulation, the released eggs continue to mature, reaching maturation two to three days later.” When the maturation process is complete, the eggs are ready to be fertilized. Poor timing during the three-week heat cycle can cause a missed breeding, he explains.
The next phase is diestrus “which maintains high progesterone levels,” Dr. Hood says. Lasting 60 to 65 days, this cycle is when the dog is pregnant or in a resting phase. You can detect pregnancy using ultrasound between 22 and 26 days. “Radiographic confirmation where the fetal skeletons can be visualized is after 45 days,” she adds.
Dr. Hood recommends feeding pregnant dogs puppy food which has extra calories and nutrients. They should also have a bed or nesting area that’s warm and secluded in preparation for them to whelp. It’s also a good idea to keep the numbers for emergency veterinary hospitals on hand if there are any complications during whelping.
The final phase, anestrus, is a resting period between diestrus and the next heat cycle. During this phase, estrogen and progesterone levels are low. In anestrus, the dog gives birth, or the uterus repairs itself for the next cycle, Dr. Hood says. Anestrus can last anywhere from 4 to 10 months.
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