Frequently (and not so frequently) Asked Questions
BRIEF: How do avocados affect horses?
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).
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!