There are many articles out there by googling "Grape poisoning in dogs"
Heres one that mentions toxic effects from eatinf 9 oz to two pounds but there is no reference to the size of the dogs. Raisins are actually considered more toxic as the toxins are concentrated. Since symptoms don't appear for 24 hours I would give your vet a call just to be safe.. http://www.savegsd.org/grapes.htm
It is probably too late now, but I would have made him throw up. I think for his size and just a few grapes Cooper will be ok. When Jake ate grapes the vet had me make him throw up and then I took him in. Jake ate 2 pounds of grapes and had to spend several days in the hospital. They did blood levels when I took him in and then checked them every couple of hours and even with treatment his levels rose before leveling off and then going back down. I'm sure if I hadn't taken him in he would have died.
I would definitely call the vet. Sambuca got into a large bag of grapes this spring. Because we realized it quickly, they had me induce vomiting and he was able to vomit everything back up. I hope he is o.k. Let us know what the vet says.
My dogs have eaten the grapes right off the vine ! ....... I realized what they were doing, right away and picked off all the grape clusters..... geesh, we can't have grapes inside the fenced yard I guess....
He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion.
That is EXACTLY how SU's bosses Lab died suddenly. She also got in to the trash of thrown out grapes. Not sure if the shriveled up ones contain more of the toxicity, or not....but she became very sick and was gone within 24 hour because they were totally unaware of what can happen with grapes.