What Are the Causes of Weakness in Kittens?

Also known as failure to thrive, fading kitten syndrome generally occurs early on. It could result from birth defects, infection or low birth weight. If kittens are born outside in the cold, hypothermia can do them in, as their bodily functions rapidly go downhill. Less common is hyperthermia, when kittens are too hot. They can dehydrate and exhaust themselves panting for air. During their first week of life, kittens have no ability to regulate body temperature, so they need a "just right" environment.

Fleas do more than make kittens itchy. They can kill. Young kittens with flea infestations often fall prey to anemia caused by fleas sucking their blood. Flea anemia is probably the No. 1 cause of death in household kittens, Veterinary Partner notes. If you see fleas on your mama cat or kittens, take them to the vet. While a flea dip or topical treatment may help an older kitten, a blood transfusion might be necessary to save a younger kitten's life.

If kittens in the litter appear weak, look for any obvious environmental factors. Perhaps you are cleaning the area they're in with any strong chemicals or disinfectant, or their space is poorly ventilated. If it's a large litter, check if the mother cat has enough nipples to feed all the kittens or if a small kitten cannot compete with his siblings for nourishment. If there's not enough food for all, you might need to supplement with commercially available kitten milk replacer.

Because kittens have immature immune systems, they're especially vulnerable to viral or bacterial infections. Kittens often pick up the feline herpesvirus from their mother while still in the womb. If your kittens start sneezing and become lethargic or their eyes gunk up, herpesvirus is probably the culprit. While the virus stays with the cat for the rest of his life, your vet can treat the symptoms.

Sometimes, the mother cat wants nothing to do with her kittens. If that's the case, you need to find a nursing mother willing to take on a kitten or two, or depending on the size of the litter, a few nursing mothers willing to take on kittens. Since that's unlikely, there’s a solid chance you’ll have to take on the task of feeding the kittens yourself. Talk to your vet about feeding kitten milk replacer and the care required for young kittens.

Neonatal isoerythrolysis occurs when newborn kittens have a different blood type than their mother. After they drink the early nutritious milk, called colostrum, the antibodies in the colostrum begin destroying the kitten's red blood cells. Healthy at birth, some kittens weaken rapidly and start dying off. The mother cat has type B blood, while the kittens with type A blood are affected. Any kittens with type B blood or type AB blood can continue to nurse and should be OK. Although affected kittens often die, if they are removed from their mother and either fed with kitten milk replacer or nurse from a type A blood substitute mother temporarily, they can be put back with their natural mother within four days. By then she is producing milk and not colostrum.