8 Types of Abnormal Heat in Dogs

Abnormal heat in dogs is a common reproductive problem female dogs go through, especially those under 2 years. Abnormalities in the sexual cycle of bitches vary, which is not only frustrating to pet owners but also a major challenge for dog breeders.

Causes of abnormal heat in dogs vary depending on the type, such as split heat, absent heat, silent heat, prolonged heat, or any other. There are a few special precautions to take when a female dog is in heat, especially when she experiences any of the abnormal heat highlighted below.

Your veterinarian will also come in handy especially if you wish to breed a dog experiencing any of these heat problems.

Related: 5 Reasons Why Your Dog’s Nipples are Enlarged

split heat in dogs and abnormal heat

Types of abnormal heat in dogs

There are several types of abnormal heat in dogs and can be hard for pet owners or even dog breeders to know when a female dog is in heat. Below we highlight 8 common types and what causes them.

1. Split heat in dogs

Split heat happens when a female dog goes into heat and displays the normal signs of a dog in heat in the proestrus phase (first phase) but fails to move to the next phase (estrus phase). Instead, the dog goes out of heat without neither being receptive to male dogs nor ready to mate or breed.

Split heat is common among young female dogs and is a result of a lack of pituitary output of luteinizing hormone (LH). Low LH levels mean the ovaries cannot generate follicles, which in turn reduces the impact of serum progesterone, and as a result, the heat cycle is hindered.

It’s advisable to work with your veterinarian if you plan to breed your dog during this time. However, note that there are risks associated with breeding a dog with split heat, including the possibility of pyometra.

Pyometra is a serious and potentially life-threatening uterine infection in dogs who have not been spayed. It’s more common in older dogs, but it can happen at any age. The condition occurs when the uterus fills with pus and becomes enlarged. Symptoms of pyometra in dogs include fever, lethargy, loss of appetite, and vomiting.

2. Absent heat in dogs

Absent heat in dogs occurs when the heat is completely missed or when the dog does not experience the normal heat cycle. Absent heat is common among younger bitches under 2 years, especially the smaller breeds. If your dog is more than 2 years old and experiences missed heat then you need to seek veterinary help.

Causes of absent heat in dogs

There are several reasons behind the absence of normal heat in female dogs. Notable causes of absent heat include:

1. Spaying

Spaying is a surgical procedure (also called ovariohysterectomy) where the ovaries and uterus are removed to sterilize a female dog. If a veterinarian performs a procedure to only remove the ovaries, that procedure is called ovariectomy. A female dog that has been spayed cannot go into heat.

2. Hormone treatment

A female dog treated with hormones such as progesterone or androgen will not experience heat while under treatment and for a few months after. Corticosteroid is a drug that resembles the hormone cortisol and has the same effect on female dogs.

3. Malnutrition

A female dog suffering from malnutrition will not be able to go into heat. Such as a dog is weak and unstable, which makes it hard for her to have a cycle. However, she will be able to once she gets well-fed, strong, stable, and healthy.

4. Hypothyroidism

Older female dogs are more prone to hypothyroidism, a condition where the thyroid fails to create and release enough thyroid hormone. As a result, metabolism will slow down, the dog will feel lethargic all the time, and may even start to gain weight. Hypothyroidism can cause absent heat as the dog will not be in good health or strong enough.

5. Ovarian hypoplasia

Ovarian hypoplasia is a case where ovaries fail to grow to sexual maturity and cannot produce enough estrogen. As a result, the mammary glands and vulva remain underdeveloped. Ovarian hypoplasia may be caused by abnormalities in sex chromosomes. A few cases of absent heat in dogs have been associated with immune-mediated ovarian inflammation. Ovarian tumors can also play a role in the absence of heat in female dogs.

3. Silent heat in dogs

Silent heat in dogs occurs when a female goes through her heat cycle but doesn’t show obvious signs, such as swelling of the vulva, vaginal discharge, charm to male dogs, or mounting behavior. Silent heat makes it difficult to know when she’s ready to mate and can last for a few days to several weeks.

If you suspect your dog is having a silent heat, consult a veterinarian to measure progesterone levels and confirm if the ovarian functions are normal. Keep in mind that a dog experiencing silent heat may still be fertile and can be bred.

Silent heat in dogs can be caused by autoimmune diseases such as oophoritis. Though rare in dogs, autoimmune oophoritis is a disease where the body’s immune system attacks the ovaries. This causes ovarian inflammation, atrophy, and fibrosis. If the effect is too much, the ovaries will not function properly hence the failure of a female dog to show any signs of heat.

Related: 7 Reasons Why a Dog in Heat is Bleeding Too Much

Symptoms of silent heat in dogs

The most common symptoms of silent heat in dogs include the lack of signs synonymous with a dog in heat. Such signs include a swollen vulva, blood-tinged vaginal discharge, excessive licking of the genital area, being receptive to male dogs sniffing and licking the vulva, frequent urination, change in tail position, excessive wagging of the tail, and mounting or humping behavior.

Symptoms of silent heat in dogs

4. Prolonged estrus in dogs

Prolonged estrus is an abnormal heat in dogs that occurs when the first phase (proestrus) of the heat cycle lasts for 3 weeks or longer and ovulation does not occur. The dog will still show the signs of heat, such as vulvar swelling, vaginal discharge, attracting male dogs, etc.

Prolonged or short heats oftentimes occur during the first heat cycles of a female dog’s life. However, things eventually go back to normal after a few heats.

Prolonged heat/estrus is mainly caused by hormonal dysfunction such as persistently elevated estrogen levels where the hormone levels remain persistently high during the first phase of the heat cycle. Persistent increase in estrogen levels can be caused by:

According to the Veterinary Society of Surgical Oncology (VSSO), ovarian tumors should be removed as soon as possible through surgical intervention. On the other hand, ovarian cysts can be monitored for some time to see if they regress or not. In case the cysts are not regressing, surgery will be deemed necessary.

5. Persistent anestrus

Anestrus is the period of sexual inactivity between two periods of sexual activity in animals that go through cyclical breeding, such as dogs. Primary persistent anestrus is a state of reproductive inactivity of a dog that has reached 2 years and still cannot experience heat cycling.

Primary persistent anestrus may be caused by malnutrition, excessive physical exertions, medical treatments that affect fertility, hormonal imbalances, genetic complications, and lack of exposure to female dogs already experiencing heat.

If a dog has previously gone through a complete heat cycle but fails to cycle again (delay of at least 18 months), this condition is called secondary persistent anestrus. This heat abnormality is often age-related and is common among dogs below 2 years because they are prone to experience irregular cycles. Older dogs can also suffer from the same due to age.

6. Recurrent estrus

This type of abnormal heat in dogs is also called shortened inter estrus interval and occurs when the interval between heat cycles is shorter than 2 months. Normally, the average time between estrus phases in two subsequent heat cycles is 7 months (4-13 months depending on breed).

During the anestrus phase (i.e. the final phase of a heat cycle), the uterus enters what is called the involution process where the endometrium is regenerated in preparation for the next heat cycle. However, if the anestrus is shorter than 2 months, what happens is a repetition of the estrus phase every 4 months or even shorter intervals, which is termed “recurrent estrus”.

Female dogs that experience recurrent estrus suffer from fertility issues as a result of the overstimulation of the ovaries and a premature decrease in progesterone levels during diestrus (i.e. the third phase of the heat cycle). Overstimulation of the ovaries can be caused by ovarian granulosa cell tumors and follicular cysts.

7. Prolonged inter estrus interval

Prolonged inter estrus interval occurs when the interval between estrus phases of two subsequent heat cycles is longer than 12 months. Notable causes of a prolonged inter estrus interval include:

  • Hypothyroidism
  • Ovarian cysts
  • Hyperadrenocorticism
  • Hyperprolactinemia
  • Progestogen
  • Androgenic or anabolic steroid substances
  • Systemic diseases
  • Poor nutrition
  • Unconducive living environment

Keep in mind that the interval between subsequent estrus phases varies depending on the breed of the dog. For example, Basenji and Tibetan Mastiff have longer inter estrus intervals compared to other breeds.

8. Premature ovarian failure

Ovarian functions reduce as a dog gets older, often beginning at the age of 6. Most dogs cease to have heat cycles when they reach 10 years old. However, there are dogs that suffer premature ovarian failure between the age of 2 and 6, and as a result, will never have the normal heat cycle.

A veterinarian can do a simple blood test to measure the concentrations of Luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones stimulate the gonads (ovaries in females and testes in male dogs) and are also called gonadotropins.

A female dog approaching or already suffering from ovarian failure will have uncharacteristically higher levels of LH and FSH. Unfortunately, there is no treatment for this condition.

Key takeaway

Female dogs ready to go in heat can experience irregular heat cycles while others can even miss the entire cycle. It’s advisable to seek veterinary help in case you feel your furry friend is experiencing any of the abnormal heats highlighted above.

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