Split heat in dogs and other abnormal heat cycles

Is your dog not going into heat?  Is she unable to conceive? While you and her may be looking forward to a litter of puppies, sometimes things don’t go smoothly. While most dogs go into heat twice a year and stay in heat for 21 days, abnormal heat cycles do occur like a silent heat or split heat in dogs.

In this article you’ll learn what is silent heat, absent heat, split heat, and other abnormalities in the estrous cycles of dogs.

IMPORTANT: the dog heat cycle can often be disrupted by serious health issues. Therefore, you should seek for a veterinary help if one of the following occurs.

Table of Contents

4 chocolate labrador retriever puppies in an old suitcase. If their mom had a silent heat, she could still have conceived these precious puppies.
If our mom had an absent heat or other abnormal heat cycle, we may not be here to brighten your day

Why hasn’t my dog had a season?

Your dog may have a medical condition or other issue preventing her cycle. The dog heat cycle has 4 stages. Dogs with normal fertility have 2 primary stages where she is preparing to get pregnant (Proestrus stage) and when she’s able to get pregnant (Estrus stage). The period of time after these 2 stages is known as the interestrus interval. That’s a long way to say, she’s not in heat. This gives her body time to recover. There are cases where a dog may not have a heat cycle or show any signs of heat. There are medical conditions that can cause irregular heat cycles such as when an infection or metabolic disease (e.g. renal failure) that can lead to systemic diseases. This will prevent her from having her normal heat cycle. 

If you are trying to breed your dog, progesterone measurement by your veterinarian through simple blood tests can help pinpoint her most fertile period. The blood tests will measure her progesterone levels to determine if she is ovulating. This can help to predict the optimal time for mating and reduce the chances of a false pregnancy or missed impregnation. This reduces the stress on both of the pet parents and the dogs.

What is Absent heat?

Absent heat is when a dog has reached sexual maturity but doesn’t come into heat even though they should have. It can occur in young dogs who have not yet come into their first heat or in mature dogs who have cycled regularly before but suddenly stopped cycling.

Primary persistent anestrus is the condition where your dog has reached 2 years of age but isn’t going into heat. Secondary persistent anestrus is a condition where your dog has had one cycle but stops having any more. There are several possible causes for persistent anestrus. These include hormonal dysfunction, ovarian tumors, and malnutrition.

Reproductive system diseases are the most common cause of absent heat. Please work with your veterinarian if your dog is presenting these symptoms.

Absent heat can also occur due to a medicine used for treating other conditions, especially if the medicine involves hormonal therapy. Talk to your veterinarian, but in most cases, the heat cycle should eventually return to normal if the treatment is applied correctly.

In our work with local animal shelters, we have seen that poor general health in a dog can also trigger a silent heat cycle to conserve energy.

Absent heat is often confused with the dog not being fully mature yet and so it’s called silent heat.

What is a Silent heat?

Silent heat happens when the dog is in heat, is receptive, can get pregnant, but does not show heat signs. Sometimes males aren’t attracted to female dogs in silent heat, but they often are.

In most cases, the signs of heat are present but are so weak that dog owners miss them. These are the lucky ones because many people struggle with their dog’s pain. For more information on how to soothe and calm your dog, please see our article Do dogs get period cramps? How to calm & soothe a dog in heat.

It’s very common for smaller dog breeds to have one or two silent heats before the normal signs of heat appear.

Silent heat shouldn’t be confused with the owner’s inexperience at noticing symptoms of a female in heat. Bloody discharge and the swelling of the vulva may easily go unnoticed or get mistaken for something else. This is especially true if your dog is really attentive to her hygiene practices. Our girl’s first heat was hard to detect other than her constant attention to her private parts.  That’s how what tipped us off.

If your dog is in silent heat, the only way to confirm the heat cycle is to take the dog to your veterinarian. They will perform a vaginal cytology and simple blood tests. Vaginal cytology is where a sample of the exfoliated epithelial cells of the vagaina are collected with a swab and examined. The vaginal cytology test will tell your veterinarian how your dog is progressing through her heat. 

A golden retriever in the arms of a veterinarian playing with a stethoscope. If she is experiencing a silent heat, it's good she is being examined.
Your veterinarian can examine your dog to determine if your dog is having a silent heat

There is an uncommon cause of a silent heat. An autoimmune disease like oophoritis (which is inflammation of the ovaries) can affect your dogs heat cycle.

It’s crucial to note that silent heat shouldn’t be confused with the owner’s inexperience at noticing symptoms. Bloody discharge and the swelling of the vulva may easily go unnoticed or get mistaken for something else, especially if the dog is orderly about her hygiene practices.

What defines Split heat?

Split heat in dogs is when the heat cycle begins but then stops before the second phase standing heat begins.

Split heat is common in young dogs during their first heat. This is because their hormonal systems are still developing and may not induce ovulation. In this case, there is no need to worry. A normal heat cycle is likely to reoccur within two to ten weeks.

However, split heat in a mature dog should be examined by a veterinarian as it could be a sign of reproductive system diseases or other health problems. It’s essential to have your dog examined to ensure that there are no underlying health issues that may be causing this problem.

What is Persistent Estrus? 

Persistent estrus is where your dog’s heat cycle continues for 6 weeks or longer. These improper ovarian functions can be caused by a hormone imbalance or ovarian tumors. As dogs usually stay in heat for 21 days, anything longer is considered to be a prolonged heat or persistent estrus.

Prolonged heat is a relatively frequent occurrence. There’s nothing to be concerned about in younger dogs. However, if prolonged heat or persistent estrus occurs when your dog has reached maturity (2-3 years), a veterinary examination is necessary.

Most often, mature dogs stay in heat for too long because of an ovarian cyst or tumor. While it sounds scary, when this condition is diagnosed early the reproductive organs can usually be surgically removed with no further health hazard. 

What causes Recurrent estrus?

Recurrent estrus is a condition where your dog goes through the estrus stage every 4 months or less. This can cause fertility issues as her ovaries are working overtime. Further, her progesterone hormone levels will be lower during the diestrus stage. Most dogs come into heat twice a year, but it’s common for dogs to cycle three or four times per year. This is especially true for smaller dog breeds.

You shouldn’t be too worried if this happens in your young dog of less than 6 months of age. Their cycling frequency usually stabilizes as they mature. However, if your dog regularly cycled before but suddenly started coming into heat more often, it’s best to take her to your veterinarian. 

Note that if you are trying to breed your dog, some of those “extra” heats may be infertile since your dog’s body needs proper time to recover from the previous cycle.

Why has my dog not gone into heat?

In addition to the above conditions, there are other medical reasons your dog may not have her normal heat cycle. Dogs usually come into heat twice a year (with exceptions for some breeds). At the same time, it’s still common if a dog doesn’t go into heat up to a year to a year and a half of age. Larger breeds tend to have a interestrus interval that is a longer period of time than a smaller breed. For example a giant breed such as a Great Dane with normal fertility we’ve seen in our veterinary clinic only went into heat every 12 months. This is especially common for their first heats. Here are some of the medical conditions that can cause your dog to not cycle.

Hypothyroidism

A dog that is 6 years old or older usually has reduced ovarian functions. At 10 years or more, not having a heat cycle is quite common.  This is commonly caused by hypothyroidism. This is where your dog’s thyroid gland doesn’t produce enough of the thyroid hormone. The same can be said for a very young dog as their ovarian functions haven’t fully matured yet.

Mammary Tumors

One area of concern is an older dog (7 years or older), that hasn’t been spayed is with her mammary glands. Mammary tumors can occur in the 5 pairs of mammary glands that your dog has.

Ovarian Hypoplasia

Another possible cause of the lack of a heat cycle is ovarian hypoplasia. This is where your dog’s ovaries don’t mature. This causes many issues due to the lack of estrogen that the ovaries fail to produce. This is because ovarian hypoplasia is where the ovaries are dysfunctional. Basically, they didn’t mature and don’t function correctly. The most common issue is the lack of a heat cycle.  Please work with your veterinarian if you suspect your dog was born with ovarian hypoplasia.They can examine epithelial cells of her vagina to check on how her ovaries are functioning.

Cystic Endometrial Hyperplasia

One concerning medical condition is called cystic endometrial hyperplasia or CEH. This rare condition can turn into an infection.  The causes are not exactly known and treatment by your veterinarian can’t be recommended more highly. 

Summary

As we’ve discussed, if your dog hasn’t had her heat cycle for more than a year requires a medical examination by your veterinarian. This is especially true if your dog has had a regular heat cycle before. Please understand this is a very complicated subject and unfortunately there are too many possible causes that may be your dog’s specific condition.  If you have any questions, concerns or suspicions, please visit your veterinarian. They can do a full exam physical exam of your dog and run some tests such as a complete blood count analysis, urinalysis, and other diagnostic testing.

You have learned what is silent heat, absent heat, split heat, and other abnormalities in the estrous cycles of dogs. This will go a long way towards a healthy and happy life with your pet dog.  And keeping your Pet Happy is what we all want.

FAQ

Question: What is absent heat?

Answer: Absent heat is when a dog has reached sexual maturity but doesn’t come into heat even though they should have. It can occur in young dogs who haven’t yet come into their first heat or in mature dogs who have cycled regularly before but suddenly stopped.

Question: What causes absent heat in dogs?

Answer: Reproductive system diseases are the most common cause of absent heat. Other possible causes include hormonal dysfunction, ovarian tumors, and malnutrition. Certain medications used for treating other conditions, especially those involving hormonal therapy, may also cause absent heat.

Question: What is silent heat?

Answer: Silent heat happens when the dog is in heat, is receptive, can get pregnant, but doesn’t show heat signs.

Question: How can silent heat be confirmed?

Answer: If your dog is in silent heat, the only way to confirm the heat cycle is to take the dog to your veterinarian. They will perform a vaginal cytology and simple blood tests to determine how your dog is progressing through her heat.

Question: What is split heat?

Answer: Split heat is when the heat cycle begins, but then stops before the second phase standing heat begins. It is common in young dogs during their first heat.

Question: What is persistent estrus?

Answer: Persistent estrus is a condition where a dog remains in heat beyond the usual 21-day cycle. It can be caused by hormonal imbalances or other underlying health issues.

Question: Can progesterone measurement help in breeding a dog?

Answer: Yes, progesterone measurement by your veterinarian through simple blood tests can help pinpoint your dog’s most fertile period, predict the optimal time for mating, and reduce the chances of a false pregnancy or missed impregnation.

This article is a part of our Dog Heat Cycle: A Comprehensive Guide for Pet Owners

Next: How long do dogs stay in heat
Previous: Symptoms of a female dog in heat

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