The toxic dose for garlic and onion that I have in my toxicology reference is 5 grams/kg of body weight. I
doubt that you are feeding that much! (ie, 400 kg horse (1000 lbs) eating 2 kgs (4 lbs)). The only toxicity I
have ever seen was in horses in North Carolina. They have an onion grass that comes up in the spring and
the horses will eat large amounts. They have very strong onion breath, have a low packed (red) cell volume,
red urine and pant like a pig when you try to ride them. They recover by simply getting them off the onion
grass. I've never heard of a real problem. Now red maple leaf toxicity is a problem and I did see horses die
from that in NC!
Cheers,
Trisha
Trisha Dowling, DVM, MS, Diplomate ACVIM & ACVCP
Associate Professor, Veterinary Clinical Pharmacology
Western College of Veterinary Medicine
Saskatoon, SK S7N 5B4
306-966-7359/FAX 306-966-7376