I'm not new to breeding, but the bitch I have is on loan and would eat me out of house and home even when not it whelp.  She is on a high protine and fat dry food and is getting around 320g each meal. If she was one of my own bitches I would be able to tell if too much or to little by they way they act. She is a large breed dog scanned with around 6.

By around this stage and going forward, most of mine had started to get too big to take in much food in one go - it wasn't so much the quantity, as the quality!   I cut back on the bulk, concentrating on protein.   The puppies will, in general, take all they need from mum before being born.   If she's a large breed with just 6 to cater for, I'd just let her eat as much, or as little really, as she wants.   Once the puppies are on the ground, and towards the end of the second week, then you need to up her intake.    Just like us, pregnant bitches shouldn't be allowed to become fat.

Thank you for that I don't do fat mums to be think its just because she not mine i worry

The last 3 weeks, I'd increase the food by about a third. You can keep the meal sizes the same and just add an extra meal in each day. It's this last few weeks when the pups are growing the fastest...

If mum whelps and when the pups are out you realise she is underweight, it can be really hard for her to put weight back on because her body is in lactation mode and any extra food you give then, just gets put into milk production.

Perhaps this is a breed-related thing , but we never increased the amount of the food our bitches had BEFORE whelping, just maybe adjust the quality.  Again.  And not one of our bitches was rail thin after whelping.    As for regaining condition, I had at least one of mine who went back into the ring.   One in particular was my Champion girl who I wanted to show, in Veterans at Crufts one more time before she was retired.   As said the puppies take all they need from mum both before and after whelping.   In fact I didn't alter the feed (other than cutting back on the bulk, pre whelping as said) until I knew how many pups had to be catered for.

I didn't increase the amount on my first litter and mum was skeletal when pups were born and it was impossible to put weight back on her until they were weaned.

In my greedy breed that needs a lot less for maintenance than say a collie of same size, I gradually increase to double rations by whelping.

After whelping almost straight to 3 times maintenance, and 4 times if over 6 pups.