Persistent Heat (Prolonged Estrus) in Cats

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Key takeaways

Persistent heat is a rare symptom in cats where the hormonal regulation of the reproductive cycle is disrupted, causing the cat to be in estrus (heat) for an abnormally prolonged period. 

  • Normal heat cycles in cats are variable, last for months, and the stages are difficult to differentiate, so identifying the symptoms of persistent heat as opposed to normal cycling can be difficult
  • Conditions that cause persistent heat include pyometra, functional cysts and tumors, and exposure to hormone replacement therapy products
  • Associated symptoms include vaginal swelling and discharge, abdominal distention, and excessive thirst and urination
  • In cases where a prolonged estrus period is accompanied by additional symptoms, emergency veterinary attention is required
  • Diagnostic tools include physical examination, blood tests, vaginal cytology, and diagnostic imaging
  • Treatments include spaying or reducing contact with hormone replacement products
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A closer look: Persistent Heat (Prolonged Estrus) in Cats


Estrus, or heat, is part of the regular sexual hormone cycle experienced by most mammals. In cats, estrus is an indication that the animal is ready to mate. Estrus should stop on its own or when the cat becomes pregnant, but will recur as long as the cat is not spayed or pregnant.

The heat cycle of cats is variable. In healthy cats, estrus can last from 1 to 21 days, and the interval between periods of estrus lasts from 2 to 19 days. Due to this variability, it is often difficult to tell if a cat’s estrus has cycled through to a latent period. Persistent heat cycles occur when the cat does not enter the rest phase, meaning she is in heat consistently.

Estrus is primarily characterized by behavior changes, including:

  • Vocalizing much more often than usual
  • Rubbing the body, including the genitals, on people or objects
  • Rolling
  • Kneading the back feet
  • Wiggling the hind end in the air (posturing)
  • Begging to go outside
  • Face rubbing

There may also be bloody vaginal discharge present, but this often goes undetected due to regular grooming.

Cats with persistent estrus will show these symptoms consistently, without cyclical breaks in behavior.

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Possible causes


Risk factors


Persistent heat is a rare symptom that only affects sexually mature female cats that have not been spayed. Feline sexual maturity develops between 6 months and 18 months of age. It is easy to mistake persistent heat for a normal healthy heat cycle in cats.

The feline sexual cycle is triggered by seasonal fluctuations in daylight hours, with cycling occurring while there is daylight for 14 to 16 hours per day. Healthy cats who have not mated may not come into heat for many months during seasons of shortened daylight. In tropical locations or house cats that are kept in well-lit homes, it is possible for cats to cycle all year.

Older unspayed cats, particularly those who have never given birth, are more likely to display persistent heat.

Cats in homes where hormone replacement therapy products are in use are also at risk. Always store medications out of reach of animals and children. Make sure application directions for topical medications are followed, including any wait times post-application, before having skin contact with animals after use.

Cats who are in heat for prolonged periods with no other symptoms are typically not in danger, although prompt veterinary attention is still recommended. Cats who experience prolonged heat alongside other symptoms such as vaginal discharge, excessive thirst and urination, or weakness require emergency veterinary attention.

Testing and diagnosis


Diagnostic tools to investigate prolonged heat include:

  • Physical examination
  • Blood work
  • Vaginal cytology (microscopic examination of cells)
  • Diagnostic imaging, such as X-ray and ultrasound to examine the uterus and ovaries

Treatment includes spaying the cat and removing any sources of exposure to supplemental hormones.

In some cases, spaying is performed without any diagnostics at all, as removing the reproductive tract clears all symptoms and eliminates any underlying reproductive condition.

Similar symptoms


Persistent heat is most often mistaken for normal heat cycles. In some cases, persistent heat occurs after spaying. This is called ovarian remnant syndrome.

Associated symptoms


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