The flap is called a primordial pouch and is located between the hind limbs underneath the belly. It is often positioned for the length of the belly of a cat in the wild or captivity, as well as housetrained cats. Very often the pouch makes the animal look as if they lost weight quickly and have been left with loose skin. 

This might also seem that this is a sign of a cat carrying some extra weight. However, the pouch has little to do with weight but all about making life easier and safer for cats. 

Although animal experts say no one knows the exact purpose of this primordial pouch, most theories agree this bit of skin, fur and fat formed into a belly flap, is unique to the species. However, the animals do not have the pouch to survive. It is a good nice-to-have but not a need-to-have. 

The Project Coordinator at FOUR PAWS’ Wild Animal Health and Husbandry, Ana Vacas, says some scientists agree that it could be used as protection for internal organs in a case of a fight, as well as for flexibility enhancement and extra space for the abdomen to expand after eating copious amounts of food. 

If you have ever seen big cats or house cats in a fight, you may have noticed that they often kick each other with their hind legs with sharp claws extended. This could potentially damage each other’s vital organs. The pouch acts as a protective fur and skin pillow against these potentially injuring kicks. 

Another theory is that it allows a cat to move faster. It stretches as the feline runs and allows flexibility during chasing prey or fleeing from another predator. The physiology thereof makes it possible for cats to perform wider or longer movements than other animals. 

Although the pouches might swing while a cat walks, it is thought not to be part of their stomachs at all. Other features include that because the pouch is a normal part of the cat’s anatomy, it does not go away with age. It will usually become visible as the cat reaches maturity. 

Ana says the fact that a cat has a prominent primordial pouch does not mean that it is overweight.  

With big cats, especially those in captivity, it is important to assess if they are overweight. Obesity in animals can lead to health problems and increase health risks especially with arthritis. 

Obesity in big cats can be diagnosed using certain indicators like a body condition score. She explains with such an assessment not a single part of the body is considered but the whole body. 

One way to tell if a cat of any size is overweight, is to look at its shape.  

Maintaining a healthy body condition is critical to all cats. Quality of life, longevity and reproductive success depend on it. The ideal felid body should be lean and muscular with defined shoulders, abdomen, and hind quarters. 

Ana emphasises that a primordial pouch is also not necessarily an indicator of good or bad health. 

“It is a physical feature more prominent in certain cats than others. There is nothing that points at it being harmful and it does not require any surgery to remove it.” 

Animal welfare scientist at the Science Unit of FOUR PAWS, Sara Da Costa Sequiera, says that a primordial pouch is not likely to influence a big cat’s behaviour. 

Primordial means that the object in question has been present since their earliest existence. With cat primordial pouches it is likely that they were named as such with a reference to the fact that cats have had these pouches since they began as a species. 

Sara says that the development of the pouches in big cats through the ages can be linked to its various functions but there is no scientific evidence that supports this. 

Whatever the real function or the origin, next time you notice a big cat or your house cat’s belly gently swaying away while they are walking or spreading out when they are lying down, just know this poses no threat and provides a benefit.