Persin, the toxic compound in avocado, is present in the leaves, flesh, seed and bark. Birds, rabbits, horses, donkeys and ruminants are highly sensitive and can develop fatal cardiovascular damage and respiratory distress — never feed avocado to them. Dogs and cats are comparatively resistant, with no confirmed deaths from persin toxicity, but ingestion can still cause vomiting and diarrhea, and swallowing the pit whole risks a life-threatening intestinal obstruction.