Why Is My Male Cat Trying To Mate With His Brother?

Normal Cat Mating Behavior

Cats do not mate for life and are polygamous, meaning males will mate with multiple females when given the opportunity (The Spruce Pets). During mating season, which occurs seasonally and is triggered by changes in daylight, unneutered male cats will roam widely in search of females in heat and compete with other males for access through fighting and ritualized displays of dominance (PetPlace). When a receptive female is detected, the male will attempt to mate by mounting her repeatedly for several hours until copulation is successful.

Lack of Access to Females

One of the most common reasons for a male cat to try mating with a sibling is simply lack of access to female cats who are in heat. Intact male cats have a strong biological drive to mate when they detect the presence of a female in heat nearby. This is triggered by feline pheromones.

If a male cat is kept strictly indoors and the only other cat in the home is a sibling, he may attempt to mate with that sibling even though it is abnormal behavior. The urge to mate is strong, and the male acts on instinct. Studies show that a male cat isolated from females in heat for prolonged periods may become frustrated and attempt mating with available cats of either gender.

The best solution in this case is to neuter the male cat. This eliminates the sex drive and inappropriate mating behavior. For intact males, providing supervised access to female cats who are spayed or not in heat can also help satisfy the biological need to seek mates. More enrichment and play can redirect energy as well.


One of the most common reasons for a male cat trying to mate with another male is to assert dominance. Cats are territorial animals and will try to establish a social hierarchy within their environment. An unneutered male cat in particular will see other cats as competition, and try to show that he is the “top cat” by mounting and thrusting against other males. This behavior is not actually sexual in nature, but rather a display of power and dominance over the other cat.

When a male cat mounts another male, he is sending the signal that he is stronger, tougher, and trying to dominate. According to Paws and Effect, this type of behavior is referred to by animal experts as “sexual aggression” even though it is not about sex or attraction. It is simply the method a male cat uses to exert control and claim status as the alpha cat in the environment.

This dominance display is especially common if there are multiple male cats in a household. The male cat wants to make it clear to the other males that he is top cat and in charge. However, dominance mounting can occur even between siblings or cats that have grown up together. The behavior stems from primal territorial instincts hard-wired into a cat’s brain.


Cats have a strong natural instinct to mate and reproduce. Much of their mating behavior is driven by biology and hormones rather than a conscious choice. Even neutered males may still feel the urge to mate from time to time, as the basic mating instinct remains despite the lack of viable sperm.

When a male cat attempts to mate with another male, including his own brother, it is often simply mistaken identity driven by the instinctual urges. The male cat’s senses tell him this is a potential mate, though that is incorrect. He does not actually recognize it is his sibling. The drive to mate can sometimes override their ability to detect the proper partner is not present.

Citing: https://www.cat-health-guide.org/catmatingbehavior.html


Stress can cause cats to engage in abnormal behaviors like attempting to mate with siblings. Cats are sensitive to environmental changes and stressors like loud noises, introduction of new pets, changes in routine, or insufficient resources. These types of situations can actually trigger their instincts to mate as an evolutionary response to perceived threats to their security or resources (Blue Cross, 2023). When stressed, the cat brain goes into an anxious “fight or flight” mode which can override normal social inhibitions.

A stressed cat may see his siblings as potential mates purely out of instinct, even if he is fixed. Stress hormones like cortisol and adrenaline can actually increase sex drive and lead neutered males to still attempt mating behaviors. This is especially true if the cat was not neutered at an early age (Amat et al., 2016). The cat is reverting to his genetic programming to try to ensure the survival of his genes. Though misguided in this context, the behavior comes from the cat’s innate drive to mate and relieve stress.

Lack of Neutering

Intact male cats have strong urges to mate that can cause a range of problematic behaviors. According to VCA Animal Hospital, the hormones testosterone and pheromones drive mating behaviors in cats that have not been neutered. Intact male cats will try to find and mate with female cats when they go into heat. If no females are available, the male cat may attempt to mate with other cats he lives with, even males or siblings.

Neutering, or castration, removes the testicles and reduces testosterone production in male cats. This greatly reduces mating urges and associated behaviors like aggression, roaming, and urine marking. According to The Wildest, neutering typically leads to positive behavior changes in male cats.

Health Issues

Occasionally medical conditions can cause mating confusion and lead to inappropriate mating behaviors between siblings. Certain neurological issues, such as epilepsy or brain tumors, may cause disorientation and poor judgment, leading cats to mistake family members for potential mates (Vetcarenews.com). Furthermore, conditions like hyperthyroidism and dementia in senior cats have been known to spark odd behaviors, possibly even sexual behaviors with inappropriate targets. Discuss any major behavioral changes with your veterinarian to rule out medical causes. Medications may help settle your cat’s instincts and curb unwanted mating attempts if health issues are contributing to the behavior.

Poor Socialization

Cats that are improperly socialized as kittens may develop behavioral issues later in life. According to research from The impact of paternity and early socialisation on the development of behaviour in the cat, kittens that are not adequately exposed to humans and other cats during their socialization period (2-7 weeks old) often become timid and fearful as adults. They are more likely to exhibit inappropriate behaviors like aggression and spraying. Kittens learn important social skills from their mothers and littermates. Those removed too early miss out on vital interactions. Undersocialized cats may see other cats, even siblings, as threats rather than companions.

How to Stop the Behavior

The most effective way to stop male cats from mating with siblings or other cats is to have them neutered. Neutering reduces testosterone levels and the desire to mate. According to veterinarians, neutering is highly recommended for male cats not intended for breeding

Providing enrichment through interactive toys, scratching posts, and daily playtime can also help redirect mating behaviors. Rotating toys to keep cats mentally stimulated is important. Vertical scratching posts allow cats to mark territory in appropriate ways.

Separating the cats at times, either in different rooms or using baby gates, can reduce mating attempts. This allows the cats their own space and breaks the mating patterns. Monitoring interactions and separating when mating behaviors occur is key.

Spaying female cats is also recommended to reduce mating behaviors. Discuss the best options with your veterinarian.

When to Seek Help

If the mating behavior between your male and male sibling cats persists despite attempts to stop it, such as providing access to female cats in heat, neutering, keeping the cats separated, and other behavioral changes, it’s a good idea to seek advice from your veterinarian.

The vet can check for potential medical issues causing the behavior, like a urinary tract infection, neurological problems, or hormonal imbalances. They can also prescribe medications or pheromone products to help curb the mating urge if it’s compulsive.

In some cases, especially if one cat is being harmed or dominated, anti-anxiety medication may be needed for the aggressor. The vet may also recommend consulting with a behavioral specialist to identify the root causes and develop a customized training plan.

Though mating attempts between siblings are unsettling, the behavior on its own doesn’t necessarily warrant rehoming a cat if it can be managed. But if quality of life is deteriorating despite earnest attempts to change the behavior, rehoming one of the cats may be kindest for both their sakes.

Don’t let the situation persist unchecked. The earlier you involve your vet, the better chance you have of resolving sibling cat mating issues through medical treatment, training techniques, or as a last resort, rehoming.

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