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If it were me, I would rest his stomach but make sure he has plenty of water.
If he is a young pup then you can make a sugary drink to keep up his energy (just sugar in the water) This was what our vet nurse recommended after my half lab ate half a tub of margarine!!! I can't recall the ratio of sugar to water though.
I would then feed him a small amount in the morning and if he is ok, another small amount later on.
It could be that he has just gobbled it down uber quick (no seriously, a lab inhaling their food - who'd have thought it? ) and it's come back up.
If he has problems with the smaller quantities it could be something more serious and a trip to the vets (thinking a blockage if he has chewed something he shouldn't)
I am not an expert, but i do have a stupid dog that is keen to eat more than she should and then be sick and/or eat something she shouldn't and then be sick.
He brought up his lunch plus carrot (of course) on the lounge floor and then proceeded to gobble it all up again! After 10mins he asked to go outside and was sick again, very cross that I would not let him stay and eat it again! Should I just starve him now?