You are completely correct in all your hunches!!! Please get a different vet!
>Vet said my bitch doesn’t have enough milk.....she said it should be squirting across the room when you squeeze
I've never been able to squirt anything from my bitch's nipples - it is notoriously difficult to 'milk' dogs(!) which is why when we supplement, we use milk replacers rather than mum's milk. You can get some out and if it's for colostrum it's worth doing, but you're not going to see it squirting across the room...
Bitches can take some days for milk to come in fully and that's fine and isn't a problem as long as pups don't lose too much weight. Day 2, her milk most definitely won't be flowing and sometimes a c-section can slow things down further.
>She said as she is feeding such a large litter she won’t have enough milk
8 pups is not a large litter for your breed and for a large breed. It's about average.
>I was advised to bottle feed all pups.
Please don't do this. As you say: Milk works by supply and demand. If you eliminate demand by bottle feeding them all, you will be stuck doing this forevermore.
So - what to do?
Supplement the bitch with fenugreek - you can get this from most health food stores and it improves milk supply. Give 2 capsules every 4 hours, until her breath smells like maple syrup. Oatmeal or porridge oats (made with water not milk) and milk thistle are also galactagogues (increase milk supply).
If you are worried about low blood sugar, take some glucose syrup on your finger and rub it on the inside of puppies' cheeks.
>This morning one bitch felt cooler than rest.
Do ensure that puppies are WARM - they cannot eat, process food or digest anything if they get too cold. They cannot manage their own body temperatures. Puppies in their first week of life should be 96-97F. If a pup is cold, the very first thing you should do is warm the pup back up to body temperature BEFORE trying to feed. You can make a pup very ill if you feed them when they are not warm. You should have a warming pad on all the time so pups can choose to move onto it or away.
If pups are fading in the first 2 weeks of life, you really need to tube feed them to save them. Nursing - whether from mum or from a bottle or syringe - takes energy. They expend far more energy doing this, than they put on - and continue to fade. Tube feeding deposits food directly to their bellies. Watch videos on YouTube about how to tube feed - there are some great ones.
Keep pups warm. Weigh them twice a day. If they lose weight from 48 hours after birth onwards, supplement - preferably by tube feeding. Keep them on the bitch. Put weak pups on the larger and more productive nipples and give them time there, removing the other pups if necessary to a warming box.