Only goats milk...any form of cows milk is bad for kittens. This happened last night witg my kitty...sadly most runts just dont make it. Its most likely something that has happened during his development. And now im going to tell you something many otherz on here told me, it is not your faukt. Some kits are just doomed from the beginning. Mine almost sounded wheezey...possibly fluid in the lungs. Eventually i took her from the momma and cuddled her till her last breath. And i named her...lucky. we are dealing with the same circumstance and i can tell you even my vet said these things happen, some are just destined to be here for only a few days. My runt lucky did bad the first day, started doing good and latching the second and then the third day it just blew up and i lost him. Same situation as your. This isnt your fault. Grieve but remember there really wasnt anything yu could do...mine wouldnt even take the bottle or syringe anyway. There is literally nothing you can do. I know you prob feel helpless, i dont know how to fix that but i do know he'll be in a better place. And now he'll get to be in kitty heaven with my little angel! Im so sorry