For owners with entire female dogs, irregular cycles can be an understandable cause for concern. Every dog’s cycle is slightly different, and each dog’s cycle will also have some normal variation. Owners need to recognise the signs of an irregular cycle so that it can be addressed by a veterinarian as soon as possible. Suppose you’re planning or trying to breed your pet. In that case, it will also be useful to understand the timings of their cycle to optimise breeding opportunities and monitor your dog’s reproductive health over time.
This post will cover what a normal reproductive cycle in a bitch should look like, the common causes of an irregular cycle, how to identify an irregular cycle, and the follow-up veterinary procedure, including diagnostic and treatment options. Depending on the issues your pet presents with, your vet will use a range of diagnostic tools to try and work out the exact cause of your pet’s irregular cycle. This enables them to tailor a specific treatment plan for your pet.
What is the normal reproductive cycle of a dog?
Most dogs will start to cycle from around 6 months old and will have two reproductive cycles a year. Some dogs may even take up to two years to start cycling! However, certain dog breeds (especially large and giant breeds), may only have one reproductive cycle a year. It is worth researching how many yearly cycles are normal for your breed.
Each cycle is made up of four stages, including proestrus, oestrus, dioestrus, and anoestrus. Each stage is determined by the relative level of each reproductive hormone present, including progesterone, oestrogen, luteinising hormone (LH), and follicle stimulating hormone (FSH). There is some normal variation for the length of each stage of the reproductive cycle in all dogs.
Stage 1: Proestrus
This stage tends to last between 6 and 11 days. The signs of proestrus are characterised by bloody discharge and a swollen vulva. This stage is usually the most noticeable to owners.
Stage 2: Oestrus
This is your pet’s fertile stage, and it usually lasts between 5 to 9 days. However, in some dogs, this stage can last up to 20 days. The signs typically include a straw-coloured vaginal discharge and behaviour that indicates receptivity to mating, such as standing to be mounted.
Stage 3: Dioestrus
This stage typically lasts for around 2 months. Your dog will have entered dioestrus when they no longer show receptivity to mating, as characterised by the oestrus stage. The vulva looks ‘normal’ and is indistinguishable from anoestrus. This stage always happens, but if extreme may be described as a “false pregnancy”.
Stage 4: Anoestrus
This is the longest reproductive stage and lasts between 4 to 5 months. During this stage, the vulval looks normal and there is no receptivity to mating. This is also the recommended stage to perform a spay procedure, as there is a reduced risk of blood loss.
What causes irregular cycles in dogs?
An irregular reproductive cycle is recognised as irregular intervals between each cycle or abnormal variations in the duration of each cycle stage. There are many multi-factorial causes for irregular cycles in dogs, the most common are mentioned below.
Age-related
Secondary persistent anoestrus is commonly seen in dogs under two years old and older dogs. This condition is defined by an 18-month delay since the last oestrus. This condition may be caused by poor nutrition, too much exercise, and certain medications.
Reproductive disease
Certain diseases can affect the reproductive organs (ovaries and uterus), which can alter hormone production and regulation. Impaired hormone balance directly impacts reproductive function and cycling.
- Ovarian tumours
- Infections e.g. E. coli and Brucellosis
- Sexual development disorders
- Autoimmune-mediated inflammation of the ovaries
- Ovarian cysts (although it’s uncommon for them to be hormonally active, it can happen)
Some dogs may experience a ‘silent heat’. In this case, reproductive function is normal, and the dog still ovulates. However, the characteristic signs of proestrus are not shown. This can be misleading for owners but is normally harmless.
Systemic disease
Diseases that originate outside the reproductive system can still impact reproductive function. Several systemic diseases commonly cause irregular cycles in dogs, including:
- Thyroid disease
- Cushing’s disease
- Kidney disease
These conditions indirectly impact the reproductive cycle, so addressing the underlying cause usually resolves any changes to your dog’s cycling.
Environmental factors
Neutering
Removing the reproductive organs removes the reproductive hormones that regulate a bitch’s cycle. Therefore, neutered females are always in a state of anoestrus and will no longer cycle. Sometimes, inadequate surgical removal of the ovaries can lead to ovarian remnant syndrome. In this case, your pet may continue to cycle and show reproductive behavioural signs.
Medications
Certain drugs can influence your pet’s reproductive cycle. If your pet starts any new medications, keep an eye on their general and reproductive health so that you can report any changes to your veterinarian. Steroids are particularly prone to affecting reproductive hormone levels, resulting in persistent anoestrus. Exposure to oestrogen-related hormones can lead to persistent oestrus.
Stress
Stress can have a huge influence on your pet’s normal reproductive cycle. The stress hormone cortisol can impact the level of reproductive hormones circulating in your pet’s body, which can inhibit coming into heat. Sources of stress could include pain and disease or changes to the home environment, such as a new pet.
Nutrition and physical activity
Malnutrition and excessive exercise can result in irregular reproductive cycles. It is a common cause of persistent anoestrus in dogs under two years old. Malnutrition interferes with normal hormone production. Regular check-ups with a vet can help to ensure your growing dog’s weight and conformation is sufficient.
What are the signs of an irregular cycle in dogs?
If your dog is experiencing irregular intervals between each cycle or prolonged or shortened stages of their reproductive cycle, this could indicate an irregular cycle. The presence of other clinical signs will vary depending on the underlying cause. For example, hypothyroidism would present with clinical signs that are unrelated to the reproductive system, including weight gain, lethargy, and coat changes. However, it will also indirectly impact cyclicity.
Knowing what is normal for your pet is the best way to identify an irregular or abnormal cycle. It is a good idea to keep a diary of your dog’s reproductive cycle, including the signs they tend to show and how long they go on for at each stage. This can help to identify any abnormal changes to their cycle and issues with their reproductive health and behaviour.
What should I do if my dog has an irregular cycle?
If you are concerned about a change in your dog’s behaviour or reproductive cycle, it is always worth getting them checked out to address the cause and prevent further issues. Contact your veterinarian as soon as possible to discuss your pet’s health.
Some causes of irregular cycles can be more serious than others. If you think your pet is seriously unwell, try to keep them comfortable and hydrated until you can see an emergency vet.
In particular, watch out for increased third, vomiting, or non-specific “off colour” in the 8 weeks after an oestrus season. These are “red flags” for a potentially fatal condition, pyometra, which may or may not involve a vaginal discharge.
How are irregular cycles diagnosed?
Your veterinarian will start by taking a thorough history, performing a basic clinical exam to screen your pet’s general health, and a detailed reproductive exam. Additional tests may be performed to determine the specific cause of an irregular cycle. The most common tests include bloodwork and imaging, such as ultrasound scanning. Other tests may include:
- Urinalysis
- Specific tests for infectious disease e.g. Brucellosis
- Hormone level tests
- Vaginal cell analysis and bacterial culture
How are irregular cycles treated in dogs?
Treating an irregular cycle will depend on the underlying cause. This is why a thorough diagnostic workup is so important in providing an effective and safe treatment regime for your pet. Here are some examples of the treatments used in common causes of irregular cycles in dogs:
- Primary/secondary persistent anoestrus – drugs such as cabergoline can be used to stimulate a reproductive cycle.
- Hypothyroidism – thyroid replacement therapy corrects the underlying cause in this case.
- Stress or drug response – stopping medications and reducing external stress factors can help restore reproductive hormone balance and cycling.
Regular check-ups can help in the prevention of certain reproductive issues. Being under or overweight can interfere with your dog’s normal reproductive cycle. Your vet can accurately assess your pet’s weight at an annual check-up to avoid this and prevent further reproductive issues.
Conclusion
Irregular cycles in female dogs can be a sign of underlying disease and affect fertility in breeding dogs. There are many multifactorial reasons as to why your dog may be experiencing irregular cycles, some may be more of a concern than others. Owners should monitor their pet’s cycles to spot any changes. Keeping a detailed log of behaviours, physical signs, and dates can greatly assist your vet in making an accurate diagnosis. Your veterinarian will be happy to help work out the cause and provide the appropriate treatment, ensuring your dog’s long-term health and reproductive well-being.
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