
I have a toy breed, and honestly go with what Barbara has said. I do my utmost not to supplement. My last litter all weighed between 2.5ozs and 2.75ozs and I just latched them on as often as possible, particularly important in the early hours after birth.
At this weight, I have never, ever found tubing successful. May be ok in a stronger, larger breed, but, at this size it just doesn't seem to be so easy. The last tiny tot I expected to lose, I refused to tube, and put her back with mum. Once I got her latched on, she stuck there like a sucker. At 12 weeks she went to a pet home as she was never going to be large enough to show, but she was a strong little tiddler.
I once tried to keep pups alive by tubing, only to ask the vet to PTS at 9 days, which was heartbreaking. I honestly think that 2oz pups are just not strong enough in the first place. Just how I feel, I fully realise that some folk will feel differently.