The first few days and weeks of a kitten's young life may seem like a total whirlwind. Although the little cuties are born helpless, with closed eyes, all of that changes—and fast. Kitten body weight usually increases by the day, literally.
Weight at Birth
Straight out of the womb, a kitten may weigh between a mere 3 and 5 ounces, according to Alley Cat Allies. This is assuming she's healthy and thriving, however. The Feline Advisory Bureau notes that an underweight newborn may be suffering from malnutrition, whether due to a malnourished queen, infection, congenital disease or any other ailment that triggers placental blood deficiencies.
Fast Weight Gain
A newborn kitten may remain tiny for the first few days of her life. After the first few days you may notice very fast weight gain. Once a kitten is about a week old, she may be twice the size she was at birth. Pretty impressive stuff!
Steady and constant growth is the key to proper kitten development. During the early days of a fluff ball's existence, expect her to grow by half an ounce every single day. If she is accomplishing this, then she's doing pretty well for herself.
Don't panic if a kitten ceases weight gain for a day or two, however. In some cases kittens reach a temporary standstill only to have an abrupt growth surge right afterward, notes the Caring Hands Humane Society.
A healthy kitten may get to between 3 and 7 ounces in her first five days. When she reaches 10 days, her weight may be anywhere from 4.5 ounces to just below 10 ounces, ideally. Right before the one-month marker, a kitten may grow to anywhere between 8 ounces and a whopping 16.75 ounces—just over a pound. Remember that all kittens are made differently, however. Also take specific breed into consideration. Some cats are just bigger than others, plain and simple. A pair of kittens can both be perfectly healthy at 4 weeks even if one weighs a pound and the other a mere 9 ounces.
If you have any concerns about your kitten's specific growth rate, take her to the veterinarian for a thorough checkup.
If you're observing a newborn kitty and her birth weight actually decreases by 10 percent during the first two days of her life, pay close attention to her. Notify a veterinarian of the situation, as it may be a life-threatening one.
Kittens continue growing at a fast and steady pace until they reach adulthood. In terms of body size, kittens are mature at around a year, indicates the ASPCA. In fact, cats of this age are so grown up they're even ready to start eating "normal" cat food, rather than kitten-formulated nosh.
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