Typical Cat Growth Timeline
Kittens grow very rapidly in the first 6 months of life. According to the WALTHAMTM Kitten Growth Charts (http://www.waltham.com/resources/kitten-growth-charts), kittens triple their birth weight between birth and 6 months of age. Most of a kitten’s rapid growth occurs in the first 16 weeks. After 6 months, kittens transition from rapid growth to a slower, steadier rate of development.
Between 6-10 months of age, kittens continue to grow but at a more modest pace. Their growth plates begin to close during this stage, signaling the approach of skeletal maturity. According to Hill’s Pet Nutrition (https://www.hillspet.com/cat-care/new-pet-parent/kitten-growth-timeline-by-week), most cats reach their adult size by 10-12 months of age, though some larger breeds may take slightly longer.
By the end of the first year, most cats have completed their rapid growth phase and reached mature adult size. Their rate of growth levels off as they fully transition into adulthood.
Why Kittens Grow Fast
Kittens experience a growth spurt in the first few months of life. According to research, kittens grow the fastest in the first 6 months, reaching about 70-80% of their adult size by 9 months old.
There are two main reasons kittens grow so quickly in their first year:
First, kittens need a very high calorie diet to support their rapid growth and development. Mother’s milk provides all the calories and nutrients needed at first. As they are weaned onto solid food around 4-6 weeks, their food intake must provide sufficient protein and calories for their high metabolic needs [1].
Second, kittens have high levels of growth hormones like growth hormone and insulin-like growth factor 1 (IGF-1) that promote rapid growth. These hormones stimulate cell division and tissue expansion during the juvenile growth phase [2].
Slowing Metabolism
As kittens grow into adult cats, their metabolism starts to slow down. Metabolism is the process by which the body converts food and oxygen into energy. Kittens have very fast metabolisms to support their rapid growth and development. But as they reach maturity around 10-12 months old, their metabolic rate decreases significantly (Hill’s Pet Nutrition, 2022).
With a slower metabolism, there is less energy available for growth. The calories from food are no longer being used up as quickly to fuel growth, so the kitten stops getting bigger. Most cats reach their full adult size by the time they are 10 months to 1 year old (Herron, 2021). The slowing metabolism is a natural part of a cat’s development that signals it has reached physical maturity.
Epiphyseal Plate Closure
Bones lengthen as the epiphyseal plates at their ends grow. According to the Animal Surgical Center, these epiphyseal plates are responsible for bone growth in juvenile animals [1]. As cats mature, the epiphyseal plates eventually calcify and close off. Once this happens, no further lengthening of the bones can occur.
The epiphyseal plates begin to close as the kitten reaches adulthood, around 10-12 months old. This prevents any additional significant bone growth, essentially fixing the cat’s size [1]. The timing of epiphyseal plate closure is determined by both genetic and environmental factors. But once closed, the cat’s skeletal growth is complete.
Reaching Adult Size
Most cats reach their adult size by around 10-12 months of age. This is because cats reach sexual maturity between 6-10 months old (https://www.hillspet.com/cat-care/behavior-appearance/when-are-cats-full-grown). Once cats are able to reproduce, there is less evolutionary pressure for them to continue growing larger in size. The average domestic cat can successfully mate and produce offspring by 10 months old, so additional growth is no longer necessary. Cats’ growth plates close and their metabolism slows around this age, causing them to stop increasing in stature.
Breed Differences
Cats of different breeds grow at varying rates and reach their adult size at different ages. Smaller breeds, like the Singapura, generally reach their full adult size quicker, by around 10-12 months of age.
Larger cat breeds, such as the Maine Coon, can take up to 2-4 years to finish growing. Maine Coon cats do not reach their full size until they are between 3 and 5 years old. This extended growth period allows them to develop into the large, robust breed they are known for.
In general, small cat breeds will stop growing by 12 months old, while larger breeds can take over 4 years to fully mature in size. The growth plates in larger cat breeds remain open longer, enabling them to continue increasing in height and length as they age. Proper nutrition and environment is key to allowing them to reach their full genetic potential.
Spay/Neuter Effects
Spaying or neutering a cat stops the production of certain hormones, like estrogen and testosterone. According to research by Salt (2023), removing these hormones can impact a cat’s growth rate to some degree.
Studies show that there is a slight difference in growth between neutered cats and intact cats. On average, neutering a male cat before 6 months resulted in the cat being about 10% smaller as an adult. For female cats spayed before 6 months, the adult size was only about 5% smaller on average (Today’s Veterinary Practice).
So while spaying and neutering may cause a cat to end up slightly smaller or larger than they would have otherwise, the effect is relatively minor. The choice of when to spay or neuter should be based more on health and behavioral considerations rather than impact on size.
Genetic Factors
A cat’s genetics play an important role in regulating their growth and determining their adult size. Just like humans, cats inherit genes from their parents that influence their development.
Some cat breeds are predisposed to be smaller or larger based on their genetic makeup. For example, Maine Coon cats often grow to be much larger than average, while Singapuras tend to stay petite and compact. These breed tendencies are rooted in the cats’ DNA.
Even within a litter, kittens can vary significantly in mature size due to genetic variation. One kitten may inherit genes inclined toward larger size from the father, while another kitten may inherit smaller size genes from the mother. This natural variation in genetics contributes to differences in growth patterns between kittens of the same breed.
Additionally, certain genetic disorders can affect a cat’s size and growth. For example, dwarfism is caused by a genetic mutation that results in kittens remaining undersized as adults. On the other end of the spectrum, acromegaly is a hormonal condition often triggered by genetic factors that leads to excessive growth.
While nutrition and other factors play a role, DNA is the basic blueprint that ultimately determines the upper limits of a cat’s growth potential. Understanding the genetic component is key to explaining why cat size can vary so greatly even within the same litter.
Source: https://en.wikipedia.org/wiki/Cat_genetics
Nutrition
Proper nutrition ensures a kitten’s growth potential can be met during the rapid growth phase. Kittens require high levels of protein, fat, vitamins and minerals to support their developing muscles, bones and organs.
According to veterinary experts, kittens should be fed a high-quality diet formulated specifically for growth that contains at least 30% protein and 20% fat from animal sources 1. Diets should also have optimal levels of essential fatty acids, vitamins like A, D and E, and minerals like calcium and phosphorus for proper bone formation.
Malnutrition during kittenhood can restrict growth. Kittens who do not receive adequate nutrition may fail to reach their genetically predisposed size. Studies show that kittens fed nutrient-deficient diets have lower weight gain and smaller skeletal size 2. Therefore, proper nutrition during the first year of rapid development is crucial.
Health Issues
Illnesses and health problems can slow growth in young kittens. Kittens are particularly susceptible to common feline diseases and parasites like intestinal worms, fleas, feline panleukopenia, and upper respiratory infections. If a kitten contracts any of these illnesses, their body’s resources go towards fighting off the infection rather than growing. Treatment and recovery from illness takes time and energy away from normal development.
Other chronic or serious diseases that may stunt growth include feline immunodeficiency virus (FIV), feline leukemia virus, and kidney or liver disease. These can cause nutritional deficits, metabolic issues, or simply divert energy away from growth. Kittens or cats with chronic health conditions often have smaller stature and fail to reach their expected adult size.
Ensuring proper nutrition, minimizing parasites through preventatives like flea/tick and deworming treatments, and vaccinating for panleukopenia and respiratory diseases can help kittens stay healthy and grow at a normal rate. Working closely with a veterinarian to monitor health and treat any issues is key to helping kittens thrive.