FKS in orphaned kitten

Question
I have a 3 1/2 week old kitten who has been doing great until the last few days.  She suckles heartily at first then quits and her daily consumption of formula is at about 75% of what it should be.  I've tried hand feeding her softened kitten crunchers with only moderate success.  At our animal shelter, we have a mom with 4 kittens that are maybe a week younger but now are at the same weight as my kitten.  Should I try to re-introduce my orphan to the nursing mom?  I had tried this about 10 days ago with this  kitten and another that I lost but, they outweighed the others and none of them were getting enough.  I found the 2 newbies screaming off to the side on the 2nd morning.  I had to remove them because the 4 littler ones had also started losing weight after 2 days.  The nursing kittens are now the same weight or more than my orphan.  I'd hate to lose another to FKS if you think the momma cat will help.

Answer
Roberta,

It couldn't hurt to try the kitten with the nursing mom again, I would suggest sticking around to watch and see if mom accepts this little one. If she isn't willing to accept this baby I would suggest talking with your vet to see if tube feeding is an option. I would also try a high quality canned kitten food like Wellness over moistened kibble, you can mix milk replacer with the kitten food til it's soupy and try teaching her to lap that mixture. Syringe feeding this mixture in the interim will help to ensure that she is getting the nutrition that she needs.

Kind regards,

Ali