kitten not gaining weight

Question
my 3 month old female kitten isn't gaining weight her brother same age is three times her size what can i do?

Answer
Hi Aimee.  You should get her to the vet.  The most common reasons for stunted growth are infection and severe parasitic infestation.  The vet will probably deworm her, since most kittens have worms.  Let the vet know you also have the brother - they may or may not send home deworming medication for him, but you'll need to know his weight.

There are all kinds of infections that can cause a kitten not to put on weight.  Some are just random bacterial infections, and with a good antibiotic, the kitten can recover and begin to grow as she should.  Some, however, are viral and can't be cured.  These include the Feline Leukemia Virus (which is not the cancer that it sounds like), the Feline AIDS Virus and Feline Infectious Peritonitis.  Your kitten is just old enough to be tested for Feline Leukemia and Feline AIDS.  Even if she was tested previously, I would recommend a retest, since tests run prior to 12 weeks can sometimes be falsely negative.  Unfortunately, there is no good test for Feline Infectious Peritonitis.

If the female is positive for either disease, the brother should be tested also, and if he is negative, the two should be separated, especially if the disease is Feline Leukemia.  I personally keep AIDS positive cats with negative cats because it takes a penetrating bite wound to spread, and it has never spread in my friendly household.  But there is always a risk.  Leukemia, however, spreads through friendly contact such as grooming each other and sharing food and water bowls.  Negative cats should never be kept with positive cats.  Unfortunately, both diseases are considered ultimately fatal, as is Feline Infectious Peritonitis.  Fortunately, they are all far less common than parasites and other kittenhood infections that can cause slow growth.

Also, be sure to keep an eye on her stools.  If necessary, separate her for a few days to see if they're of a normal consistency.  Diarrhea will cause a kitten to waste away.  There are a couple germs in addition to parasitic worms that can cause diarrhea.  Most notably, they are coccidia and giardia.  If you bring in a stool sample and it tests positive for either of these germs, your vet would probably want to treat the brother, too, since they share litter boxes.  These germs have been known to kill kittens if left untreated, so an antibiotic must be given.  If she has diarrhea but she doesn't respond to antibiotics, a food change may be in order.  You should discuss the best way to go about this with the vet.  A prescription food may be recommended.  I also advocate grain-free diets.

Best wishes.  I hope she's big and strong soon!

Jessica