Cats

Do cats mate with their siblings?


Understanding the intricate behaviors of cats, especially when it comes to mating, can often raise eyebrows and curiosity among pet owners. One question I get with notable frequency is whether cats can mate with their siblings. The short answer is yes – brother and sister cats can mate. And I have to say, it’s better to ask than to assume something, and then end up with a litter of unwanted kittens and inbreeding-related health issues. But why do they mate and why you shouldn’t let them is for a longer discussion. You want to know more? 🙂


While I am a veterinarian, this article is not intended to replace professional veterinary advice. If you have any medical concerns about your pet, consult your vet immediately. Always seek professional assistance if you are unsure of your pet’s health.


Incest in animal kingdom

Cats possess deep-rooted natural instincts when it comes to choosing their mates, often driven by the need for reproduction rather than companionship. Their behavior is profoundly influenced by the concept of territory, which not only defines their living space but also plays a crucial role in their social structures. Within these territories, feral cats establish complex social hierarchies that can affect mating choices, often prioritizing mates based on dominance or territory control. Understanding these behaviors is key to comprehending how and why cats interact with potential mates, including siblings, within their defined spaces.

Incest is something we humans came up with, based on our moral and ethical values. And although it did happen from time to time, mostly to secure power for future dynasties (remember the Pharaohs or those huge powerful houses in the middle ages?), it’s not something that’s accepted nowadays. And there are good reasons for that. 

But for animals, it’s a different story. They don’t have the same concept of incest and will mate with whoever is available – brother, sister, even parent with offspring. It doesn’t really matter to them. While it’s not that common for cat siblings to mate when they are living freely outside and have other partners to choose from, it does happen if you have indoor cats. 

Sometimes people forget that cats or dogs don’t have the same moral values as we do and are surprised when they learn that cats are not very picky when it comes to their love life. They assume siblings just wouldn’t do it. Well…that would be a mistake, sorry 🤷‍♀️

Why do sibling cats mate?

Usually, cat siblings who grow up together love playing and spending time with each other during their kittenhood. However, once they reach reproduction maturity and go into heat, things change.

Cats have the same reproductive drive as other mammals and are genetically programmed to pass on their genes, i.e. reproduce. 

Once their hormones tell them they are ready to mate, they will do it. And if there are no other sexual partners available, they will mate with each other. 

Their hormones, their whole programming tells them they have to mate. It’s as simple as that. That drive is so strong that if there is no one else available, they will mate with siblings or even parents.

And it’s not just cats. If you keep sibling dogs without neutering them, chances are they will mate too. 

Can brother and sister cats have kittens?

Cats can have their first heat (and therefore be able to have kittens) around 6 months of age, but it can be as soon as 4 months. 

They are seasonally polyestrous, which means they have multiple cycles during their breeding season. This means that cats can actually go into heat as often as every 2-3 weeks, sometimes year-round and they continue to go into heat well into their senior years. One heat cycle can last from a few days to a few weeks. 

When male and female cat siblings become fertile, they can mate and have kittens together. But just like with humans, there are certain risks associated with incest.

Why you shouldn’t let your sibling cats mate – Risks associated with cat inbreeding

Inbreeding is the mating of closely related animals. This can happen between brother and sister, or parents and their kittens.

Pedigree cats have traditionally been mated with close relatives. Nowadays, the practice of breeding close relatives (siblings or parents) is not well accepted. And there are good reasons for that. Thanks to scientific advancements, we now know more about inbreeding depression, hereditary disorders, and genetics in general. We just know more than we used to, so our views changed. 

This is something you need to think about before you actually buy a pet from a breeder. If you want a pedigree cat, make sure the breeder is not inbreeding his cats. 

There are risks associated with inbreeding, and some of these risks can be deadly for kittens. Inbreeding depression is one of those risks – it’s when an animal’s ability to survive and reproduce is reduced because of genetic defects that are passed down from the parents.

Hereditary disorders are also more common in animals that have been inbred. These disorders can be anything from heart defects to problems with the immune system. 

Some of the risks of cats mating with their siblings or parents include:

  • Increased risk of genetic disorders, defects, and abnormalities 
  • Higher probability of having stillborn kittens or weak kittens that die soon after birth
  • A smaller litter size
  • Reduced fertility
  • Lower immunity and higher susceptibility to infections

So, while it’s natural for cats to mate with their siblings if they have the opportunity, it should be avoided.

do cat siblings mate - risks associated with inbreeding in cats

How to prevent cats from mating with a sibling (or a parent)

Once your cats reach maturity, they will mate with anyone that’s available. That’s a fact. 

Sometimes people think they will be able to separate them, but I just can’t really imagine how, unless you keep them in separate rooms most of the time and endure the whole variety of cat heat signs every 2 weeks. 

Just think about it – cats can actually go into heat as often as every 2-3 weeks, sometimes year-round when you have indoor cats. The heat duration can vary from a few days to a few weeks.

So, if you don’t want your animals to have babies with each other, the best thing you can do is to neuter or spay them to avoid any unwanted litters. Not only will it help with population control but also reduce the risk of certain cancers and health problems associated with reproduction.

While cats mating with their siblings is not something that we would do ourselves, it’s important to remember that they don’t have the same moral compass as we do. It’s just their instinct. 

But, as a responsible pet owner, you need to do what’s best for them, and spaying or neutering is the best way to go. Not only will it help with population control but also reduce the risk of certain health problems.

Talk to your vet if you have sibling cats. He can help you decide if spaying or neutering is the best option for your pets.

So, that’s it from me, thank you for reading! ☺️

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