What is feline superfetation? Promiscuity in human terms.

Superfetation occurs when about 10 percent of cats come into heat when pregnant. This results in a second set of eggs being fertilised before the first litter is born. It is a result of the breeding capabilities of the domestic cat.

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Superfecundation illustration – pregnant cats. By MikeB

Normally pregnancy suppresses the sexual physiology of the female. However, female cats sometimes break the norms. There is another phase of sexual receptivity during the pregnancy cycle when there is a low level of pregnancy hormone.

The additional period of heat occurs around 3 or 6 weeks into pregnancy which lasts 9 weeks. This period of heat during pregnancy usually occurs between the 21st and 24th day. If the female mates again and her eggs are fertilised, she’ll carry two litters at different stages of development.

The unborn kittens develop along side each other at different stages. When the female gives birth to the older kittens, she may also give birth to the younger ones prematurely causing their death.

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If the younger ones go on to full term the mother will end up with too many kittens to fed as she’ll have a shortage of nipples 🙂 The mother normally finds a way to cope.

Dr Morris’s contribution

Dr Desmond Morris uses graphic language to describe this phenomenon. But he first says that female cats break a fundamental rule of reproductive behavior which is that the condition of pregnancy suppresses the female’s sexual physiology. They break what he considers to be a golden rule.

Feline superfetation

Those that do have low levels of the pregnancy hormone in their systems. The additional heat cycle sends “the expectant mothers out on the tiles again where if they are mated once more, they will be fertilised again and then carry two litters at two different stages of development”.

He writes that,

“When she gives birth to the older litter, the upheaval of delivery may lead to the younger litter being ejected as well….If, on the other hand they manage to hang on inside the uterus they may be born successfully at full term three or six weeks later”.

This as mentioned cause a second problem, “an almost impossible demand for nipples and milk supply”. If she copes with this in part or totally, she is able to “contribute even more spectacularly to the feline population explosion”.


An associated female cat behavior is similarly described as ‘superfecundation’. This describes females having a litter of kittens in which the individual kittens have different fathers. This arises because female cats mate with different tomcats during the same session even if they have a favorite. The range of appearances of kittens within a litter may not be due to genetic inheritance from one father but because they have different fathers. This can account for a startling range of kittens in a litter. You can read more on this by clicking on this link.

Morris says that superfecundation is the product of domestic cats living much closer to each other compared to their wild cat ancestors living in large home ranges and relatively rarely meeting cats of the same species. In the wild Morris says that “the chances of a whole group of tom-cats coming together in one spot when a wild female is on heat [is remote]”.

P.S. If your cat has experienced feline superfetation or superfecundation please share in a comment. Thanks.

Useful tag. Click to see the articles: Cat behavior

Note: sources for news articles are carefully selected but the news is often not independently verified.

Michael Broad

Hi, I'm a 74-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I love nature, cats and all animals. I am concerned about their welfare. If you want to read more click here.

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10 Responses

  1. MAGACatLover says:

    Another day under joe biden presidency… Cats keep getting more inflation !

  2. Tarek Fahmy says:

    It is new for me

  3. Brittany Hiebert says:

    I believe this just happened to my cat. At one point during her pregnancy she was acting like she was in heat again and the neighborhood Tom’s were coming around again. She just gave birth and two of the kittens were stillborn and looked underdeveloped. One of them was born in a gush a fluid but its sac was fully intact with the placenta and everything. I had to struggle to break the sac as it was very thick. Neither kitten ever breathed or moved.

  4. Jane Carter says:

    Thanks for writing about this Michael. I did not know that the two pregnancies could develop alongside each other. I am aware that females can have different fathers to each kitten in one litter, and they can hold a pregnancy in abeyance when times are hard, but this is a new, amazing fact for me. Truly incredible. Mother cats must be some of the most capable in the world.

    • Michael Broad says:

      Yes, it is all geared up for survival. The alternative is ‘superfecundation’ which is what you refer to.

  5. Frances A Danna says:

    Thank you for writing about this, Michael. I had never heard of this happening. I had no idea what the word ‘superfetation’ meant. Ten percent of pregnant cats coming into heat sounds like any awfully high rate of occurrence. The outcomes definitely sound unfavorable. ?

  6. Albert Schepis says:

    Oh my gosh, that’s horrible. This is the first I’ve ever heard of this and I’m 63.

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