Overview
Inbreeding is the mating of closely related cats, such as siblings or cousins, and results in a higher degree of homozygosity in the offspring (Casal, 2022). Inbreeding increases the chances of deleterious recessive alleles manifesting in homozygous offspring, leading to health issues known as inbreeding depression. Effects of inbreeding depression in cats include increased neonatal mortality, birth defects, impaired immunity, reduced fertility, and shorter lifespan (Matsumoto, 2021). The higher the inbreeding coefficient (a number representing how closely related the parents are), the more severe the inbreeding depression becomes.
Health Risks
Inbreeding between brother and sister cats increases the risk of genetic defects and health problems in the offspring. This is because closely related cats are more likely to carry the same recessive genes, which can lead to issues when paired together in offspring. Some health problems commonly seen in kittens from brother-sister matings include congenital heart defects, cleft lip or palate, intestinal issues, eye abnormalities, skeletal deformities, and neurological problems. The level of inbreeding depression tends to increase with successive generations of inbreeding. So kittens from the second or third generation of sibling matings often have more severe issues.
Inbreeding leads to decreased heterozygosity, which reduces the gene pool diversity that supports health and survival. Multiple studies show higher kitten mortality rates from inbred litters compared to outbred litters. One study found a mortality rate of 35% for kittens from brother-sister matings, compared to a rate of 10% for non-inbred kittens from the general population.
Behavioral Issues
Inbreeding in cats can lead to a number of potential behavioral problems in the offspring. Some common issues seen in inbred kittens and cats include increased aggression, fearfulness, anxiety, obsessive behaviors, and sensitivity to physical contact. According to the Cat Bandit blog, “Some of these behaviors can include aggression towards other cats or humans, fearfulness or anxiety, withdrawal, and sensitivity to physical contact. These behavioral abnormalities are likely the result of the expression of detrimental recessive genes in the inbred cats.”
Research has shown that as the degree of inbreeding increases, so does the likelihood of behavioral problems. A major study published in the Journal of Feline Medicine and Surgery in 2022 found a significant correlation between higher inbreeding coefficients and an increase in undesirable behaviors. The most common problems seen were heightened aggression and fearfulness.
While the exact causes are not fully understood, it’s believed that reduced genetic diversity from inbreeding results in developmental issues in parts of the brain related to social behaviors. The combination of multiple negative recessive genes also likely contributes to impaired socialization and abnormal responses to stimuli. Proper socialization and enrichment from kittenhood may help reduce problematic behaviors, but cannot fully eliminate the risks associated with inbreeding.
Sources:
https://blog.catbandit.com/understanding-the-risks-of-inbreeding-in-cats/
https://journals.sagepub.com/doi/full/10.1177/1098612X221118755
Physical Abnormalities
Inbreeding between brother and sister cats increases the risk of physical abnormalities and birth defects. Some potential physical defects from inbreeding include:
- Crooked or misaligned jaws
- Cleft palate
- Heart defects
- Lung abnormalities
- Abnormal eye set or eye issues
- Short or twisted limbs
- Spinal deformities such as kinked tails
- Failure of organs to develop properly
According to research published in the Journal of Feline Medicine and Surgery, the rate of physical abnormalities in kittens from moderately inbred cats is around 5-6%, much higher than the general cat population. Severely inbred cats can have rates over 20%.[1]
Physical defects are one of the most obvious and concerning results of inbreeding in cats. While not all inbred kittens will have birth defects, they are at a significantly higher risk compared to outbred cats.
Lower Life Expectancy
Inbreeding tends to lower the life expectancy of cats. According to Cats.com, inbred cats do not live longer than non-inbred cats. In fact, in many cases the opposite is true, and the lifespan of inbred cats is reduced compared to non-inbred cats.
One source notes that there is no definitive answer for how long an inbred cat will live, but most die before reaching their second birthday (Justagric.com). The average lifespan of an inbred cat is estimated to be around 10 years or less, and in some cases inbred cats die unexpectedly at a young age (Derppets.com).
The reduced life expectancy of inbred cats is likely due to the many health issues and complications they face from inbreeding. With higher rates of genetic defects and abnormalities, inbred cats tend to have weaker immune systems and shorter lifespans.
Difficult Births
Inbreeding between brother and sister cats can lead to an increased risk of birthing complications. When closely related cats mate, it increases the chances of genetic abnormalities in the offspring that can impact development and viability. Some potential birthing issues that may arise from inbreeding cats include:
Smaller litter size – Inbred litters tend to be smaller, with fewer viable kittens. This is due to higher rates of developmental issues and prenatal mortality.
Stillbirths – Highly inbred kittens have a greater likelihood of being stillborn or dying shortly after birth. Stillbirth rates are estimated to be 2-3 times higher in litters from brother-sister matings.
Birth defects – Physical abnormalities caused by inbreeding can make delivery difficult or impossible. Defects such as cleft palate or defective limbs may obstruct the birthing process.
Weak or underdeveloped kittens – Inbreeding may result in kittens that are born small, frail, or failing to thrive. This can lead to complications like low birth weight and problems nursing.
Prolonged or difficult labor – Factors like small pelvis size or abnormal kitten positioning could impede the natural birthing process. Inbred queens often experience prolonged, painful labors.
Neonatal mortality – Even kittens born alive and apparently healthy may fail to survive more than a few days due to inbreeding-related weaknesses.
Emergency measures like cesarean sections may be required to deliver inbred litters safely. However, the risks associated with difficult births can still jeopardize the health of both the kittens and mother cat.
Population Impacts
Inbreeding in feral and stray cat populations can have negative effects on the overall health and sustainability of those populations. When closely related cats mate, it increases the chances of genetic abnormalities and medical issues in kittens. According to one source, “Inbred cats don’t live long and have more health problems, especially heart defects” (Bowen Island Undercurrent).
Common issues seen in inbred kittens include heart defects, kidney disease, immune system disorders, and skeletal abnormalities. These health problems then impact the feral cat population as a whole by decreasing the average lifespan and increasing mortality rates. With more kittens dying young or being born with debilitating defects, it becomes difficult for the overall population to thrive and sustain itself.
Inbreeding also reduces genetic diversity over time, as fewer bloodlines are represented in each new generation of kittens. This lack of diversity makes the population more vulnerable to disease outbreaks and environmental changes. Essentially, inbreeding threatens both the short-term and long-term viability of feral cat colonies by propagating defective genes and decreasing adaptability.
TNR (trap-neuter-return) programs for feral cats are one way to combat inbreeding and its impacts. By preventing closely related cats from breeding, these programs can improve the health of future generations. However, in areas with small, isolated colonies, inbreeding may still occur even after TNR efforts. Overall, the effects of inbreeding underscore the importance of population management for sustained feral cat colony health.
Ethical Concerns
Inbreeding between siblings or close relatives raises a number of ethical issues. Some experts argue that it is morally wrong for brother and sister cats to breed, as it violates the natural order and standard mating practices
There are ethical concerns that inbreeding could lead to decreased health and quality of life for any resulting kittens. Intentionally breeding cats that are closely related, with the knowledge that it may lead to birth defects, deformities, or health complications, can be seen as ethically questionable.
Some shelters and breeding associations see controlled, intentional inbreeding as unethical and irresponsible. The goal of many ethical breeders is to promote cat health through careful selection of unrelated mates. Responsible breeders aim to avoid inbreeding which could propagate genetic diseases. There are ethical arguments that humans have a duty to prevent suffering and health issues in domestic cats under their care.
Overall, many experts argue that due to health and welfare concerns, as well as violating natural mating tendencies, it is ethically problematic for sibling cats to intentionally breed. There are moral arguments against human actions that facilitate problematic inbreeding.
Breeding Regulations
There are several laws and regulations around breeding cats, particularly related to inbreeding:
In the United States, there are no federal laws prohibiting cat inbreeding, and it is generally not regulated at the state level either. However, some states and municipalities do have laws prohibiting the sale of animals from inbred litters. For example, Pennsylvania prohibits the sale of animals from litters with a coefficient of inbreeding higher than 12.5%.
In the United Kingdom, the Animal Welfare Act prohibits the breeding of closely related cats if it results in suffering or abnormalities. Breeders must obtain a license from their local authority.
Some cat registries and breeder associations, like The International Cat Association (TICA), have voluntary codes of ethics that prohibit harmful inbreeding. TICA’s code limits parentage to no more than 12.5% inbreeding across five generations.
While laws are limited, ethical breeders aim to avoid inbreeding depression through careful selection of unrelated breeding pairs. Conscientious breeders track pedigrees over multiple generations.
Preventing Inbreeding
The most effective way to prevent accidental inbreeding between brother and sister cats is to have them sterilized through spaying or neutering procedures. By having cats fixed, their reproductive organs are removed, eliminating the possibility of pregnancy. According to the Catbandit blog, “Spaying and neutering are essential practices to prevent inbreeding. By sterilizing cats, we eliminate the possibility of accidental mating and reduce the urge for them to mate” (Source).
It’s recommended to have kittens spayed or neutered around 6 months of age before they reach sexual maturity. For adult cats, sterilization can happen at any age. Consult with a veterinarian to schedule the procedures. Aside from preventing accidental litters, spaying and neutering provides health and behavioral benefits too.
If keeping intact cats in the same home, closely supervise them during heat cycles. Isolate female cats for the few weeks they are in heat to prevent mating from occurring. Never purposefully breed closely related cats.