Do Cats Mate With Their Siblings?

Can sibling cats mate with each other? Is this behavior normal? We have taken a deep dive into this subject and have all the answers owners need. Read on to learn more about sibling cats mating and what to do about it.

Danielle DeGroot

Last Updated: October 10, 2023 | 9 min read

two cats mating outside

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Do cats mate with their siblings? The question comes up fairly often, especially when people adopt or already have brother and sister kitties in their care. Of course, the topic is one people may be uncomfortable talking about, but as with many other aspects of pet care, it must be addressed.

Owning sibling cats can be wonderful, giving your pets a friend for life. Keeping sibling kittens together offers many advantages. Along with having constant companionship, the sibling felines can provide comfort, affection, and support for each other. Adopting a brother and sister or two same-sex siblings can also help with behavioral training and, of course, double the amount of furry feline cuteness in your house.

Along with these positive benefits, sibling cats face challenges, including mating each other. Let’s take a more detailed look at this topic and answer some common questions owners may have. Though it may be a difficult topic, there are some things owners of litter mates need to know.

Can Sibling Cats Mate?

Yes, sibling cats can mate with each other, and it is a very common behavior. While this is natural behavior, it is unhealthy, as any breeding of intact kitties will often result in a pregnancy. Interbreeding among felines often leads to very unhealthy kittens suffering from various health problems. Owners must take steps to prevent this from occurring. Spaying and neutering kittens appropriately is the best way to prevent interbreeding pregnancies and offspring.

Why Do Sibling Cats Mate?

Unlike humans, felines do not have an understanding of a moral compass or boundaries on sexual interaction with siblings. This behavior is inappropriate and illegal among humans, but kitties differ from us regarding morals. Kitties from the same litter are often the best of friends as kittens grow into maturity. Once a feline reaches sexual maturity, their bodies want to reproduce. This reproductive drive is quite strong. If felines do not have alternate mating partners, their siblings may become mating partners. While this is typical behavior and driven by natural instinct, it’s not something pet owners want to allow to happen.

Along with the risk of interbreeding and unwanted pregnancies, this is not a behavior cat owners want to allow to become common or permissible. In some cases, cats will even mate with their parents for the same reasons they mate with siblings. Both scenarios are something owners want to work to prevent.

What Happens If A Brother And Sister Cat Mate?

If the sibling kitties are intact, most likely, a pregnancy will be the result. The kittens have a high possibility of having genetic defects and serious health concerns. Several risks are associated with inbreeding, including inbreeding depression, which means they will have difficulty surviving and reproducing due to hereditary genetic defects. These risks occur anytime related felines, like siblings or parent and child, mate, resulting in a pregnancy.

Risks Associated With Felines Inbreeding

  1. Higher risk of genetic defects, hereditary disorders, and developmental abnormalities
  2. Smaller litter size.
  3. Poor development.
  4. Less likely chance of survival.
  5. Decreased fertility rates and lower chances of reproducing.
  6. Poor health, lower functioning immune system, and higher susceptibility to infection and illness.
  7. Risk of congenital disabilities including cleft palate, heart defects, kidney malfunction, and skeletal abnormalities.
  8. Physical deformities include abnormal and asymmetrical eye setting, misaligned jaws, and crooked noses.
  9. Increased neonatal illness and mortality.
  10. Odd behavior and temperamental issues, including aggressiveness, depression, isolation, and poor socialization.

There is a chance kittens will be normal and healthy, but that cannot be known until they are born. For the most part, allowing siblings to mate and produce offspring is not recommended.

Do Breeders Use Inbreeding?

Breeders sometimes mate closely related felines to create and maintain purebred genetic lines. The practice is referred to as controlled inbreeding and line breeding. It is not recommended that pet owners or home breeders try this. Too much inbreeding can lead to something called inbreeding depression, which refers to a phenomenon of reduced fertility rates and decreased survival in the progeny of closely related animals. As with any species, when siblings mate, it reduces the chance of survival. With kitties, unwanted sibling litter adds to the already very serious feline overpopulation.

Tips To Prevent Sibling Cats From Mating

If you have sibling kitties and are concerned about them mating, there are a few things to do to discourage this behavior.

Spay & Neuter

Spaying and neutering kittens at the appropriate time, generally between four and five months old, is the most critical step feline owners can take to prevent siblings from mating and other feline interbreeding. Felines are polyestrous, which means they go into heat several times a year. Once a female has been spayed, she will no longer experience estrus, also called heat. The urge for mating and reproducing will no longer be highly active in spayed cats. The same goes for neutering male kitties. Neutering them prevents them from reproducing.

The best, most surefire way to prevent interpreting and unwanted litters of kittens is to spay and neuter your kitten at the appropriate time. If you have an intact adult purr baby, they can still be spayed or neutered. You will need to speak with your veterinarian about the best weight and time to go about it, but overall, your pet will be healthier after the procedure and recovery time.

Adopting Same Sex Siblings

Another way to prevent sibling cats mating is to simply avoid the possibility of it happening altogether by adopting siblings of the same sex. That choice will rule out any chance of mating or procreation.

Separating Cats

Along with spaying and neutering kittens at the appropriate time, separating felines is another highly effective method to keep them from mating. Unfortunately, this type of quarantine is often done out of necessity when kitties are highly agitated. Separating male and female siblings will prevent mating, but it is not a long-term solution. Unless you can permanently separate these animals in the same home for the long run, putting them in separate secure rooms will only stop the behavior at that specific time. Separation is a short-term method that works, but it is not one that owners can rely on to use regularly.

If your kitties are intact, male or female, isolation may be the only effective method if a female kitty is in heat or a male kitty senses her pheromones. Isolating a female kitty in heat will require her to be separated from other felines for six to seven days. Female kitties often yowl loudly and constantly and seek affection when they enter the heat cycle. Isolation should begin as soon as owners start to notice heat signs.

Male cats do not experience heat, but when they smell pheromones of intact females, it will cause an instinctual reaction. Once this happens, he must stay away from any female cat. Isolating an intact male feline usually results in an amping up of aggressive behavior, including spraying, loud vocalization, and causing physical damage to walls, furniture, and other household items. It is especially true if he is in the same house as a female kitty in heat. The male kitty will likely smell her and hear her yowling, increasing his need to escape isolation.


Some owners have had luck training their sibling kitties not to mate with each other. It is a tricky task and will require patience and dedication on the part of the owner. One must be very observant and redirect the behavior when they see it happening. Offering kitties plenty of distractions like new toys, treats, catnip, CBD oil or CBD treats, and plenty of options for physical exercise through interactive toys and climbing structures is helpful. A bored kitty is likelier to try to get away with bad behavior, whether mating-related or not. So, providing your purr babies with plenty of interaction and entertainment goes a long way.

Owners may want to consider pheromone sprays and diffusers to calm felines down, reduce sexual aggression, and help deter some of this behavior.

Birth Control For Cats

Birth control for felines is more than just a frequently asked question. It is a reality. One method includes the use of synthetically produced progesterone. Progestin is a hormone that can postpone the heat cycle and help with the effects felines experience from false pregnancy. The generic name for this drug is Megestrol acetate, which comes under several brand names, including Ovaban and Megace. The medication is taken orally, either in a pill or liquid form. (Pregnant women should take extra caution when administering this medication to their pets. Wearing gloves and washing hands immediately after handling is advisable). Megestrol acetate can prevent heat and stop pregnancy from occurring in felines by halting estrus. It is often given in circumstances when an animal may need to wait for the spay procedure.

This drug has other uses in both humans and animals. It works to treat skin or behavior conditions in felines as well as benign prostatic hypertrophy in male dogs. Megestrol acetate also postpones the female heat cycle and treats false pregnancy in canines.

Megestrol acetate has human uses as well. It has been used in patients with metastatic breast cancer, womb cancer, AIDS patients, and other uses to improve appetite and gain weight.

Male kitties can also undergo a vasectomy procedure instead of neutering. Vasectomy in felines works the same way as in male humans, leaving the testes intact but preventing males from impregnating a female. While not as common as spay and neuter, some owners opt for this procedure for their male kitties.

New Research

Further research is ongoing into non-surgical birth control for felines. This area has made significant progress; research was recently shared in the Nature Communications journal. Researchers prevented ovulation and conception in female felines for at least two years using a single-dose viral vector containing something called anti-Müllerian hormone (AMH). This hormone is naturally produced in the ovaries. In their research, scientists injected this gene therapy vector into intact females and then observed them for over 2 years.

The findings showed that these animals did not produce kittens. This treatment suppressed ovarian follicle development and ovulation but did not affect other hormones. Additionally, no adverse effects were noted in any of the treated females. While this is not currently a method used for birth control in felines, it shows great potential in this area and is a much less invasive feline birth control possibility than spay and neuter surgery.

Personal Experience With Sibling Cats

I adopted two sibling kittens about 11 years ago. These rescue kittens were in a very bad situation when I adopted them. I sought medical care for them immediately and worked closely with my veterinarian to ensure they were spayed and neutered at the appropriate time. One of the first things the veterinarian made clear was that these kittens would mate with each other, resulting in more kittens. He was very concerned about ensuring that this did not happen.

Both my kitties are fixed, but I occasionally see some of this behavior. My male cat will often pounce on, mount, and try to bite the female, his sister. She does not like this attention and will, in turn, get aggressive with him, scaring him off. When they were younger, this behavior happened more often. However, I started using a loud voice, saying, “Leave it,” and offering a distraction of toys, catnip, or treats to entice the male kitty to leave his sister alone.

Though this behavior does not happen much anymore, it was of great concern to me when they were younger, especially before the spay and neuter procedures. I would highly advise anyone adopting related kitties to adopt same-sex siblings or be ready to take on the cost of spay and neuter within just a few months to prevent unwanted pregnancies from sibling interbreeding.

Frequently Asked Questions

When should I spay or neuter my kitten?

You must discuss this with your veterinarian to ensure the time is right for your unique pet. Most kittens are spayed or neutered between 4 and 5 months old. Kitties that are in shelters, rescues, and animal control care may often have the procedure early, around 8 weeks old. It is essential to perform this procedure before your kitten reaches sexual maturity, especially before females enter heat.

Spaying and neutering not only prevent pregnancy, but it also helps prevent health issues, improves behavior, and helps reduce the number of united and stray kitties in shelters and on the street.

Why is my male cat trying to mate with his brother?

While it may appear that your male kitty is trying to meet his brother, in likelihood, they are not. Male cats mounting each other is often a demonstration of aggression, stress, or dominance. Felines are not gay in the same way that humans and some other species may be. Male felines rarely try to meet or engage in intercourse with other males. In some cases, recently neutered males will rub on things, including other male kitties, but this does not stem from a sexual instinct. More often than not, homosexual-like behavior in felines shows aggression, dominance, or hormonal frustration.

Is my male cat mounting his sister a sign of mating?

In many cases, this behavior may be driven by sexual hormones. However, a male cat mounting a female cat is not always a mating attempt. This behavior may sometimes be a male cat’s way of reinforcing their dominance and social position. Male cats often rub up against, hump, and pounce on other cats and inanimate objects without the intention of mating. Male cats with mating intent often appear aggressive and may jump on, growl, and even bite the female cat.

Final Thoughts

Adopting sibling cats has many advantages. Owners get double the fuzzy, feline cuteness, and kittens have a built-in playmate and security system in their siblings. While most of the time, adopting sibling kitties is a wonderful experience, there is always the possibility that they may try to mate. Instincts and hormones drive mating, and cats do not have the ability to have the same moral compass as humans do. Coupling with a sibling is not something considered taboo for them. However, it is not healthy. Owners should take precautions like spaying and neutering their pets appropriately to prevent interbreeding among feline siblings or even feline parents and children.

If you have behavioral concerns about your cat or sibling felines whose behavior seems highly sexually charged or aggressive, it is best to contact your veterinarian and an animal behavior expert for advice on stopping this behavior safely and effectively. Our article is for informational purposes only and is not a substitute for consulting a licensed veterinarian.

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