Kittens (Old English diminutive of cat) are juvenile domesticated cats (Felis catus) that are not fully-grown. The young of species in the genus Panthera and of some other big cats are called cubs rather than kittens. Either term may be used for the young of smaller wild felids such as ocelots, caracals, and lynx, but "kitten" is usually more common for these species.
A litter of kittens usually consists of two to five kittens. They are born after a gestation that lasts between 64-67 days, with an average length of 66 days. Kittens emerge in a sac called the amnion which is bitten off and eaten by the mother cat.
For the first several weeks, kittens are unable to urinate or defecate without being stimulated by their mother. They are also unable to regulate their body temperature for the first three weeks, so kittens born in temperatures less than 27°C (80 °F) can die from exposure if they are not kept warm by their mother.
The mother's milk is very important for the kittens' nutrition and proper growth; so if possible, the kitten should not be taken from their mother for at least 8 weeks after birth. This milk transfers antibodies to the kittens, which helps protect them against infectious disease. Newborn kittens are also unable to produce concentrated urine, so have a very high requirement for fluids.
Kittens open their eyes about seven to ten days following birth. At first, the retina is poorly-developed and vision is poor. Kittens are not able to see as well as adult cats until about ten weeks after birth.
Kittens develop very quickly from about two weeks of age until their seventh week. Their coordination and strength improve, they play-fight with their litter-mates, and begin to explore the world outside the nest. They learn to wash themselves and others as well as play hunting and stalking games, showing their inborn ability as predators. These innate skills are developed by the kittens' mother or other adult cats bringing live prey to the nest. Later, the adult cats also demonstrate hunting techniques for the kittens to emulate.
As they reach three to four weeks old, the kittens are gradually weaned and begin to eat solid food, with weaning usually complete by six to eight weeks. Kittens live primarily on solid food after weaning, but usually continue to suckle from time to time until separated from their mothers. Some mother cats will scatter their kittens as early as three months of age, while others continue to look after them until they approach sexual maturity.
The gender of kittens is usually easy to determine within the age of approximately six to eight weeks, although it is possible to do so sooner. The male's urethral opening is round, whereas the female's is a slit. Another marked difference is the distance between anus and urethral opening, which is greater in males than in females.
Kittens are highly social animals and spend most of their waking hours interacting with available animals and playing. Play with other kittens peaks in the third or fourth month after birth, with more solitary hunting and stalking play peaking later, at about five months. Kittens are vulnerable to harm because they like to find dark places to hide; with sometimes fatal results if they are not watched carefully.
Although domestic kittens are commonly sent to new homes at six to eight weeks of age, it has been suggested that being with its mother and litter mates from six to twelve weeks is important for a kitten's social and behavioural development. Usually, breeders will not sell a kitten that is younger than twelve weeks, and in many jurisdictions, it is illegal to give away kittens younger than eight weeks old.
Kittens require a high-kilojoule diet that contains more protein than the diet of adult cats. From weaning until about one year of age they should be fed a diet specifically formulated for kittens. Orphaned kittens too young to eat solid food may be fed a cat milk replacement formula every two to four hours. Kittens should not be fed cow's milk because it does not provide all of the necessary nutrients. Cats are generally intolerant of sugars in their diets and both sucrose (table sugar) and lactose are not digested and cause soft stools or diarrhea. Orphaned kittens that are not urinating or defecating must be stimulated to do so after each meal by rubbing with a warm, damp washcloth at the base of their spine where the tail begins. This is vital to the kitten's survival.
However, while it is possible to rear kittens by hand, it is best to leave a kitten with its mother if at all possible. Hand-reared kittens tend to be very affectionate and more dependent on humans as adults, but can also show volatile mood swings and aggression. If a kitten develops diarrhea, it is best to seek advice from a veterinarian. The kitten may need to be de-wormed with a de-wormer at 6-8 weeks old and then again 2 weeks later.