My 43-day-old kitten isn't gaining weight. Is it time to wean?

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 :-)

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.

Some kittens do nurse longer than others, and wean at a later date. He does need to learn to eat regular food, however, you can try to wean him. To start, mix dry kitten food with kitten milk replacer formula so they recognize the taste. Smear the mixture around their mouth with your finger and let them lick it off. Once they get used to the taste, they’ll seek it out elsewhere. As he get used to this, add in more dry food, and less formula until you have completely eliminated the formula.

At 4-5 weeks, kittens should be transitioning to solid foods, so it would be best to mix in the KMR with the wet food into a sort of slurry to help with the transition and make it easier to digest. You can also weigh Cleo with a food scale or other small scale to get her weight in ounces which can help you determine how big she is. Most kittens at this age will still needed to be fed several times a day. This article also has a great guide and charts about feeding and life stages from birth to about 8 weeks of age which may be helpful! https://www.petcoach.co/article/how-to-raise-orphan-kittens/

It would be the right time to start introducing solid food gradually. Initially just mixing it with kitten milk, then over 4-5 days wean her off onto solids completely. She is too big to rely on milk only.

He is still very young and misses his mommy and his siblings. You should feed him canned kitten food, as kibble is still too hard and a kitten cannot eat enough of it. Feed him small portions 4-5 times a day and feed as much as he wants to eat, ie refill the bowl a little bit at a time. Make sure water is available but not next to the food. It needs to be about 6 feet away from the food bowl. At this age (71 days) he should weigh a little over 1kg, or 2.3lbs

It sounds like he is under weight, so I reccomend continuing the kmr every 6 hours for at-least two more weeks. Leave out kitten kibble for him at all times. If he is eating this well in two weeks, then you can incrementally reduce the amount of kmr feedings over the following week and hopefully wean him off by the end of that week. I hope that helps and hope all is well with Od.