Bottle-fed kittens not gaining weight? Should I change formula?

As long as they are all continuing to gain weight steadily you can continue to monitor them for now. It is normal to see some variation among littermates. However if they're smaller kittens show other signs are not thriving such as decreased play behavior, being isolated from the other kittens, or they stop gaining weight then you need to try to supplement formula again.

Your best bet would be to bring the kitten into your vet. They can check for any issues such as congenital problems causing the weird back arching, cleft palate that affects nursing, etc that you may need to treat differently or take particular care for. If the kitten is otherwise healthy, adding in supplemental feeding may also help with weight gain if it can't nurse enough from mom.

You should be weighing them every day or two to make sure they are gaining weight. If the little on is not gaining weight then you will know it is a problem and you will need to get it to a vet. You can use a kitchen gram scale to weigh them.

This could be a case of fading kitten syndrome which unfortunately has a poor prognosis. You can try Nutrical on her gums as well as a dab of Karo syrup to see if increasing her blood sugar helps. Unless she starts having a better suckle you will have to keep going with the dropper for feedings.

That is not normal. I recommend getting the kitten seen by a vet right away. Such a tiny baby needs to eat every few hours. Many veterinarians will use an ordinary eye dropper or small syringe to utilize as a means of dispensing the milk replacer to the kitten. Most pet stores or veterinary clinics have nursing bottles, too, but be alert to the fact that some kittens cannot suck the contents through the small nipple. You may need to actually squeeze the milk out for the kitten while having the nipple in the kitty's mouth. Warm it up a little, too, under the hot water faucet! If it is after hours at your local animal hospital, your short-term solution will be to mix an egg yolk with a can of evaporated milk (make sure it is not the sweetened condensed milk). This is only a temporary "solution" (!) and should only be used for a couple of feedings. At the first few feedings the kittens will probably only consume a few cc’s worth of milk. (There are 5cc's in a teaspoon.) You will need to feed every couple of hours at first and gradually build up time between feedings as they begin to eat more at each meal. Start by offering a small amount. If the kitten won’t eat readily from the nipple and bottle, try an eyedropper or syringe and drip a little in the mouth, adding more as the kitten's pace. Make sure that the milk just above room temperature; try not to microwave since you can cause hot spots in the milk. Follow instructions on the milk replacer for mixing and storage. You will need to contact your veterinarian if the kitten has not eaten within 24 hours or is extremely weak. Once they get the hang of it, the kittens should consume the milk replacer greedily. You can stop the feeding when the kitten begins to slow down the consumption or becomes disinterested.

At 43 days of age, it's time for Tarcisio to be weaned off milk. Milk won't be enough at this point to meet his nutritional needs, so that may be why he's not gaining weight. To help him wean and to get used to dry food, I would soak a high quality kitten formulated dry food in warm water until soft. Then mix that with kitten formula such as KMR to make a mush the consistency of oatmeal. Over the next two weeks, gradually increase the amount of dry kitten food and decrease the amount of water and KMR you use until he is eating the dry kitten food only.

At six months of age, Ritsu is way past the point of needing to nurse from his mother, and I would not encourage that behavior by giving him kitten milk replacement. It can take some kittens up to eight weeks of age to fully wean, and that's normal. He may be trying to nurse off of her for comfort, but it is concerning he's having trouble gaining weight. First thing to do is to make sure he's eating a high quality kitten formulated food, such as Hills Science diet or Royal Canin. You can try soaking the dry food in gently warmed low sodium chicken or beef broth, or tuna juice to tempt him to eat the dry food. If that works, then slowly reduce the amount of liquid you soak his food in until he's eating the dry only. Also make sure he is up to date on his deworming treatments, as intestinal worms will prevent him from gaining weight. Finally, I would have him seen by a vet for a health check. The vet can identify if there is a medical issues causing him to gain weight, such as an inability to digest nutrients properly, and can discuss treatment with you. I hope this helps :-)