I found the onion/garlic poisoning article ("Six Cases of Heinz Body
Haemolytic Anaemia Induced by Onion and/or Garlic Ingestion" - CM Edwards and
CJ Belford Aust.Vet.Prac. 26 (1) March 1996, 18-22). Excerpts below. I also
consulted my dog's internist, and she confirmed that garlic is just as
poisonous as onions in large doses. The doses given for flea control
obviously don't kill the dog, but it would be interesting to see if some
non-lethal, mild anemia develops in dogs given garlic regularly. We don't
hear about garlic poisoning of dogs as often as onion poisoning because
people don't usually have large amounts of garlic in a tasty form. A plate of
fried onion rings will do in a small or medium dog, for example, but we don't
have plates of fried garlic rings for obvious reasons.
Excerpts from the article:
"All [cases] had a history of eating onions and/or garlic. Presenting signs
included pale mucous membranes, dark urine and haemoglobinuria, inappropriate
micturation [urination], abdominal pain, vomiting, diarrhea."
"Questioning of the owners revealed a history of onion ingestion in pizza,
mincemeat or Chinese food in four cases. In Case A [cat], the food included a
large amount of garlic as well, whilst Case F (Rottweiler) ate solely garlic
and had no access to onions. The amount of onion and/or garlic consumed in
each case is unknown."
"It has been shown, in dogs, that daily ingestion of up to 11 grams of raw
onions per kilogram of bodyweight produced anaemia with a gradual onset,
whilst 15 or more grams per kilogram of bodyweight caused sudden onset
anaemia within two or three days."
"It would appear that raw, dry or cooked onion has the ability to caused
haemolytic anemia. . . . Onions and garlic are members of the Allium family.
It is therefore likely that garlic contains the same toxic component as