Adapting to onions
Anonymous said: Hello Dr Ferox! A while ago I read that it was dangerous to feed dogs foods like onions. This came as a huge shock to me considering that on my family farm in Brazil, the rural people there can't really be considered "good" pet owners because of lack of education/different priorities. Dogs are mostly left to fend for themselves & are fed leftovers. Most of it is seasoned with PLENTY of onion & the dog still live to very old age. Can dogs really adapt this easily to a toxic food? Thank you!
Onions specifically cause a Heinz body anaemia, where oxidative damage affects the red blood cells, causing them to break apart and leave these little dots (the Heinz bodies) everywhere. Toxicity is dose dependent so eating a whole bunch of onion in one go can do it (about 200g for a 20kg dog, or a medium to large onion) or eating smaller amounts over a longer period of time, destroying a few more red blood cells each time it’s ingested.
Red blood cells do regenerate, but not instantly. It takes a while to regrow new ones, and if the amount of red blood cells being damaged each day is less than the dog is capable of regenerating, they may show no clinical ill effects. This doesn’t mean that it’s safe or good to do, because all it takes is one episode of the dog gorging itself on food that’s suddenly available.
Over many generations dogs that are more resistant to the chronic low levels of toxin exposure may evolve, but I’d suspect in this case the dogs are not eating all that much total human food, not if they’re mostly fending for themselves, and if these meals have lots of other ingredients they may be consuming less onion than you think.
The typical poisoning cases we see are dogs that have eaten well with meals containing onion, or eaten a whole lot of it in one go, such as leftovers from a barbecue.
