Frail foster kitten nursing non-mom: Enough milk? Should I see a vet?

No, giving Muffin milk replacement will not turn that milk into her milk. It's concerning she is very skinny, and she needs a kitten formulated dry food to eat while nursing. The kitten food will give her added calories, protein, and calcium to support nursing her kittens, and I would run out to get that food now. Leave a bowl out of that for her to eat as needed. It's very important she is healthy to support nursing her kittens, so I would also recommend a visit with the vet in the next day or two for a health check. Be sure to bring her kittens with her. Best of luck.

Your cat may not be far along enough yet to produce milk. I'm not sure how old this kitten is, but it may be old enough to start on a kitten food gruel. I'd have him seen by a vet now to get an age and help getting it fed. Best of luck.

Milk replacement for cats is fine to give her, but please know it's very serious when a cat won't eat. If they go long enough without eating (about 72 hours), they will develop a fatty liver. A fatty liver is fatal without treatment. You need to take her into a vet now, especially since she is nursing kittens. She may have a severe post-partum illness. Take her kittens with you to the vet.

The best way to determine if your cat is producing milk is by observing the kittens. Newborns spend long hours nursing - up to 8 hours per day - with sessions lasting up to 45 minutes. When the mother's milk is being let down, the kittens will each latch onto a preferred nipple and stay there. If you observe closely you will be able to see their little mouths and tongues moving from the suckling action. Often their ears may move as well. Nursing kittens will knead the mother's abdomen which is an important stimulus to milk let down. After a feeding session, the kittens will have round, full bellies and will fall asleep. Ideally, healthy kittens who are nursing well will gain 7-10 grams every day. They can, and should, be weighed every few days to confirm gains.

I would not recommend transferring kittens over and back between mothers. I recommend a full health check by your vet to assess your own cat to determine if there is any medical reason such as an infection which is reducing her ability to make milk. If this is not reversible then transferring them to the other cat to foster until weaned is a possibility but not all mothers will take to new kittens and she may reject or attack them in which case you would need to bottle feed them.

It is possible that she has milk. Let mama tend to them but keep bottle feeding them. If they are not hungry because they got enough milk from mama, they will drink less or not at all. She is obviously a very good mama. Suckling is also an important comfort factor, even if there is no milk. It gives the kittens security and bonds. Leave them with their mama until they are 12 weeks old. She will teach them everything they need to know including how to use the litter box, what to eat and what not, hunting, etc., and you will get well adjusted kittens without behavioral problems. And thank you for taking such good care of them! Please let me know if you have any other questions or concerns and I would be more than happy to help you further. Please take the time to mark this question as helpful or not as it helps us to improve on the quality of our answers to other pet owners. Thank you kindly!

Make sure the kittens stay warm. If they are not nursing well or she is not producing milk then you can bottle feed them to help. She should be fed kitten food as it has more calories and nutrients to help her keep her weight up and produce enough milk