My dog had one pup by c section friday. (4 days ago) pups weight has gone from 270g at birth, dropping to 197g 2 days ago, then 187 yesterday & now 190g this morning. Vet said she has a strong suck reflex, mum is producing milk (not huge amounts, but some). we are now having to syringe feed with puppy milk as she has been loosing weight when feeding with mum. She's been feeding from mum every 2 hours for 20-30 mins a time, but the weight is falling off her. shes actually stabilised & gained slightly now feeding her puppy milk too.
Any thoughts & advice would be gratefully received.

https://vcahospitals.com/know-your-pet/puppy-fading-puppy-syndrome-in-dogs
Here is info about Fading Puppy Syndrome - there are loads of websites with information too

Is the puppy noisy - FPS normally presents with the puppies making a noise like a seagull.   Very distressing to everybody.   Many times a 'Sectioned puppy will lose a bit from birth weight, but quickly make it back up again as they nurse ... and after all, a singleton has the whole milk bar to get at.   Mum could have had more puppies, but whatever caused them to be lost could have affected this puppy too - she was just strong enough constitutionally, to make it into the world.   Even at this age, you could try a little natural yogurt on the tongue - just a tiny amount.   This is a probiotic so could help.   She will need to be kept extra warm, not having any siblings to snuggle with and another thing that occurs to me - mum may run into mastitis if she starts producing a lot of milk, and it's not being drawn off sufficiently, with just one puppy - she needs to be rotated amongst the teats.

You can really only keep a close eye on her (nice to have a female singleton puppy - all too often they are males although the one we had, was female) and hope for the best.   Good luck.

Click Here: Fading Puppy Syndrome

she does seam very content, strong & drinking well & often, but just not gaining weight after a huge drop. Heat fine (heatpad & mum). its the lack of weight gain is very worrying for us