Kitten growth: the milestones that actually matter

In cats the sensitive period for socialisation sits roughly between the second and the seventh week of life, so much earlier than in dogs and often before the kitten reaches its permanent home. During those weeks daily contact with different people, with ordinary household noise and with gentle handling determines how well the adult cat will tolerate the carrier, the veterinary visit and visitors. That is why the quality of what happens before rehoming matters as much as what you do afterwards.

Separation from mother and littermates before eight weeks is more often associated with behavioural problems in the adult cat, in particular aggressive behaviour during play and difficulty handling contact. Many codes of good practice point to twelve weeks as an appropriate age, because by then the vaccination course has started, weaning is complete and social learning within the litter has happened.

Weight is the only indicator you can measure at home, at no cost, that anticipates almost every problem. In the first weeks you need a kitchen scale accurate to the gram; later a household scale is enough, weighing yourself first and then yourself holding the cat. The practical rule is simple: in the early weeks a healthy kitten gains weight every day, and a weight that has not moved for two consecutive days is already a reason to call the clinic.

The values above are indicative and do not replace comparison with the individual trajectory: a large breed kitten may exceed them entirely normally, a small framed one may stay below without being ill. What counts is the shape of the curve. Growth that slows and picks up again is compatible with a period of adjustment; growth that stops or reverses never is.

Unlike weight, these milestones need no equipment: observation and a recorded date are enough. They are mainly useful for estimating the age of a found kitten, checking that development is on track, and booking veterinary appointments at the right moment.

The kitten calendar follows the same logic as the puppy one: antibodies passed on by the mother protect during the early weeks and at the same time interfere with the vaccine response, so the primary course involves several doses at intervals and does not finish before sixteen weeks of age. Components considered essential in cats cover panleukopenia, herpesvirus and calicivirus; feline leukaemia vaccination is decided on lifestyle grounds, and is recommended after testing for kittens that will have outdoor access.

• FIV and FeLV testing: done before introducing the kitten to a household with other cats and before feline leukaemia vaccination.
• Internal parasite treatment: in kittens it is repeated at short intervals in the early weeks, because roundworm infection is common and can pass through the milk.
• Ear check: ear mites are common in kittens from colonies and produce itching and dark debris.
• Electronic identification: a microchip can be placed in a kitten, and registration should be completed before any access outdoors.
• Recording dates: the next due date is always counted from the dose actually given, not from the month it had been planned for.

A female kitten can have her first season as early as four months, and in many females it arrives between five and nine months depending on the season and available daylight. That is far earlier than most owners expect, and it is why unplanned pregnancies in domestic cats often involve animals still thought of as kittens. In males, hormone driven behaviours such as marking with strongly scented urine and the tendency to roam usually appear between five and ten months.

The practical consequence is that the neutering decision has to be made before the problem appears, not after. Several professional bodies now point to neutering by five months as appropriate in the domestic cat, aiming to prevent a first pregnancy and the onset of marking. The choice should still be discussed with your vet, taking into account weight, health status and the living conditions of the individual cat.

Kitten play is a predatory sequence: spot, stalk, chase, grab. If the only available target is human hands and feet, the adult cat will keep using them as a target, with a force that at eight months is no longer tolerable. The remedy is not to punish the grab, which raises arousal and teaches the cat to distrust hands, but to move the target onto objects that move away from the body and to end every session with a successful catch and a small meal, as in the natural sequence.

• Short frequent sessions of 5 to 10 minutes several times a day work better than one long session.
• Hands are never toys, at any stage: the rule applies from day one, because a kitten cannot tell exceptions apart.
• A second kitten of similar age greatly reduces play directed at people, but doubles cost and management: it is a deliberate choice, not a fix.
• One litter tray per cat plus a spare, in separate quiet places, with fine unscented substrate: most elimination problems come from management, not from the cat.
• Reachable vertical surfaces and a stable scratching post as tall as the stretched cat: in kittens the habit forms within weeks and then stays.

A kitten has very small energy reserves and deteriorates quickly. Several situations that would allow a few hours of watching in an adult cat need immediate assessment in an animal a few weeks old.

• Weight unchanged over two consecutive weighings, or any weight loss at all under six months of age.
• Complete refusal of food for more than twelve hours in a kitten under three months.
• Diarrhoea with lethargy, or diarrhoea lasting more than twenty four hours in a small kitten, because dehydration follows fast.
• A body that feels cold to the touch and a kitten that does not respond to handling: in very young animals this is an emergency.
• Breathing difficulty, open mouth breathing or respiratory noise audible from a distance, at any time.
• Straining to urinate without producing urine, especially in males after six months: one of the few genuine emergencies in the young cat.