Ingestion of avocados may cause life-threatening toxicity in some animals, including severe and/or fatal heart damage. Vomiting and diarrhea has been observed in dogs but their risk of poisoning is less than in other animals. Pets of particular concern include birds, horses, mice, rabbits, and guinea pigs.

Avocado

Signs and symptoms of toxicity: Signs of toxicity include fatigue, difficulty breathing, and abnormal swelling.

Toxic consumption: There is no established threshold for toxicity. All incidents of exposure should be reported immediately.

References:
Foods Hazards: Avocado. The MERCK Manual Pet Health Edition Web Site. http://www.merckmanuals.com/vet/toxicology/food_hazards/avocado.html Updated 5/2013. Accessed January 2, 2015.