Frequently (and not so frequently) Asked Questions
BRIEF: How do avocados affect horses?
QUESTION:
I live in an avocado orchard, moved my horses home this weekend, and my
equine vet is on vacation for two weeks so I am unable to ask him about
this. I've heard that avocado leaves are toxic to horses so I trimmed the
trees back fairly well around the paddocks (they aren't ours and are a cash
crop so I want to do the minimum trimming) and crawled around the whole
paddock area on hands and knees picking up all the dried avocado leaves
which had blown in over the past week since we had started fencing the
area. I don't know how conscienctious I need to be about collecting either
dry or fresh leaves off the ground in the paddocks and whether it would be
important to prune the trees more drastically to prevent any contact.
Today I've seen a couple of the horses playing with everything and trying
to prune all the plants within reach (they are very well fed, but awfully
curious). They've gotten a few avocado leaves that I've seen, (maybe more
when I'm not there), and have also been playing with the other plants
outside the fences. I'm pruning everything back pretty well now, and my
main worry is the avocados, but if you're game, I would love to know about
all the plants which border the paddocks, whether they are safe, mildly
toxic or worse. The other plants out there are purple potato vine, one of
the solanums, I believe in the deadly nightshade family, plumbago, peach,
mock orange, banks roses, bouganvilla, jasmine, myoporum, pittisporum,
pepper, and eucalyptus--sounds like a California garden guide doesn't it).
ANSWER:
Some of the guatemalean varieties are toxic to livestock. They cause
cessation of lactation and lesions in the mammary gland and at a high
enough dose, fatal respiratory complications. Other varieties don't seem to
cause a problem. Unfortunately, the trees are a lot harder to tell apart
than the fruit. I am from California, and I never could get those varieties
straight...
Art Craigmill in the UC Davis Department of Environmental Toxicology and
Frank Galey at the State vet Diagnostic lab in Davis can help you. Art has
done research on the avacado/lactation problem and Frank sees more
poisoning cases than anyone else in California. Good luck!