EJTCM commented about avocado. I admit I have given my birds avocado in the past to no obvious ill effect they ate all the flesh and left the skin and stone stripped clean. However I found this on another forum and I personally think that I will avoid avocado in future.
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Are avocado toxic to chickens?
Yes, they are. Avocado leaves, fruit, bark, seed...everything. Toxic to anything with hooves and feathers. Dogs, cats, and humans are fine with avos.
'Poisonous' or 'toxic' doesn't always mean 'drop down dead at one bite.' The toxic chemicals in avocados act a bit like rattlesnake venom, in that it kills the tissue it touches. The toxin tends to lodge in the internal organs, especially in the heart, liver, kidneys, lungs, and mammary glands (in mammals). Most of the animals end up dying of heart failure, pulmonary edema, and liver and kidney failure. Symptoms often don't show up for 12-24 hours.
I grow avocados commercially, and I've had my goats get into them. I had a doe nearly die after jumping the fence into the avocado trees. A friend's doe ate a few leaves a week, then got into a large section of it - she was treated, recovered, and then died a month later from the massive heart damage and pulmonary edema (the necropsy showed her heart was so badly damaged that it couldn't pump fluid out of the lung tissue - she literally drowned in her own body fluid).
With birds, it often relates to body size - the amount of toxin the body can process out is greater in birds of large body size. A chicken could eat an amount that would kill a parakeet in a few hours and not show symptoms. A turkey could eat still more. It also depends on healing time. I ran my turkeys in the avocado orchard one year, and they did eat the fallen fruit. They didn't die. But they were smaller at butchering, and their hearts were enlarged, and their livers were ummmm....lumpy.
Not much is known about avocado toxicity, because the climate belt for growing them is so restricted. The thing is that we just don't see the damage or the animals being "sick," because of the nature of the toxin. Somebody's bird ate some and was "fine," so it must be okay. Not true.
The damage can be cumulative as well as the result of one large ingestion incident - a few leaves or fruit a week can do as much damage as the total amount in one day. I wouldn't make it a habit to feed avocados to chickens, but in all reality, a few fruit a year won't likely cause a problem in your flock.
Just because we can eat it doesn't mean other animals can process the chemicals in the same foods. Dogs and chocolate, and cats and aspirin, for example.