Ingestion of avocado (Persea americana) has been associated with development of myocardial necrosis in mammals and birds and with sterile mastitis in lactating mammals. Cattle, goats, horses, mice, rabbits, guinea pigs, rats, sheep, budgerigars, canaries, cockatiels, ostriches, chickens, turkeys, and fish are susceptible to these conditions after avocado ingestion. Caged birds seem more sensitive to the effects of avocado, whereas chickens and turkeys seem more resistant. Although a single case report exists of two dogs developing myocardial damage after avocado ingestion, dogs seem relatively resistant compared with other species.
Etiology of Avocado Toxicosis in Animals
Ingestion of fruit, leaves, stems, and seeds of avocado has been associated with toxicosis in animals; leaves are the most toxic part. The Guatemalan varieties of avocado have been most commonly associated with toxicosis.
When purified, the toxic principle in avocado, persin, causes mastitis in lactating mice at 60–100 mg/kg, and dosages >100 mg/kg result in myocardial necrosis. Goats develop severe mastitis after ingesting 20 g of leaves/kg, and 30 g of leaves/kg typically results in cardiac injury. Acute cardiac failure occurred in sheep fed avocado leaves at 25 g/kg for 5 days; 5.5 g/kg of leaves fed for 21 days or 2.5 g/kg for 32 days caused chronic cardiac insufficiency. Budgerigars fed 1 g of avocado fruit developed agitation and feather pulling, and 8.7 g of mashed avocado fruit resulted in death within 48 hours. Myocardial injury, mastitis Mastitis in Mares Mastitis in a mare. It is most common in the drying-off period. Acute mastitis occurs occasionally in lactating mares, most commonly in the drying-off period, in one or both glands. Streptococcus... read more , and colic Overview of Colic in Horses Depiction of a horse’s GI tract as viewed from the right side. In its strictest definition, the term “colic” means abdominal pain. Throughout the years, it has become a broad term for a variety... read more have been reported in horses ingesting avocado fruit and/or leaves.
Pathogenesis of Avocado Toxicosis in Animals
Avocado ingestion causes necrosis and hemorrhage of mammary gland epithelium in lactating mammals and myocardial necrosis in birds and mammals. Ingestion of persin, isolated from avocado leaves, has caused lesions similar to those reported in cases of natural ingestion of avocado.
Clinical Findings of Avocado Toxicosis in Animals
In lactating animals, sterile mastitis occurs within 24 hours of ingestion of avocado, accompanied by a 75% decrease in milk production. Affected mammary glands are firm and swollen and produce watery, curdled milk. Lactation may provide a degree of protection against myocardial injury when small amounts of avocado are ingested. In nonlactating mammals, or after ingesting a large amount of avocado, myocardial insufficiency may develop within 24–48 hours of ingestion and may be characterized by lethargy, respiratory distress, subcutaneous edema, cyanosis, cough, exercise intolerance, and death. Horses may develop edema of the head, tongue, and breast region. Birds develop lethargy, dyspnea, anorexia, and subcutaneous edema of the neck and pectoral regions, and they may die.
Mammary glands are edematous and reddened in animals with avocado toxicosis, with watery, curdled milk. In animals with cardiac insufficiency, congestion of lungs and liver typically occurs, often with dependent subcutaneous edema. Pulmonary edema and free fluid may develop within the abdominal cavity, pericardial sac, and thoracic cavity. The heart may have pale streaks. Histopathologic lesions in the mammary gland include degeneration and necrosis of secretory epithelium, with interstitial edema and hemorrhage. Myocardial lesions include degeneration and necrosis of myocardial fibers, most pronounced in ventricular walls and septum; interstitial hemorrhage and/or edema may be present. In horses, symmetric ischemic myopathy of the head muscles and tongue, as well as ischemic myelomalacia of the lumbar spinal cord, have been reported.
Diagnosis of Avocado Toxicosis in Animals
Clinical evaluation and history of exposure
Diagnosis of avocado toxicosis relies on history of exposure and clinical signs. There are no readily available specific tests that confirm diagnosis. Differential diagnoses include other causes of mastitis Mastitis in Large Animals This newly calved heifer died from peracute, severe Staphylococcus aureus infection. Mastitis, or inflammation of the mammary gland, is predominantly caused by bacterial pathogens and... read more (eg, infectious) and other myocardial disorders, including ionophore toxicosis Toxic Myopathy in Poultry Myofiber degeneration and necrosis, with satellite cell and fibroblast proliferation and infiltration of histiocytes. Hematoxylin and eosin stain. 200X. Bar = 100 mcm. Ionophore toxicity causes... read more , yew toxicosis Range Plants of Temperate North America Poisonous plants are among the important causes of economic loss to the livestock industry and should be considered when evaluating illness and decreased productivity (see Table: Poisonous Range... read more , vitamin E/selenium deficiency Nutritional Myopathies in Ruminants and Pigs Young Boer goat kid with white muscle disease. The patient can move its legs normally but is too weak to stand. CK and AST concentrations were elevated on serum biochemical evaluation. The goat... read more , gossypol toxicosis Gossypol Poisoning in Animals Gossypol is produced naturally by the glands of the cotton plant. Although all animals are susceptible to gossypol toxicity, monogastrics, preruminants, immature ruminants, and poultry are affected... read more , cardiac glycoside toxicosis (eg, oleander), cardiomyopathy Specific Cardiac Diseases Mitral valve leaflets, especially the tips, are thickened due to myxomatous degeneration. There is also a linear (horizontal) left atrial tear present. Myxomatous degeneration is a process of... read more , and infectious myocarditis.
Treatment of Avocado Toxicosis in Animals
NSAIDs and analgesics may benefit patients with mastitis caused by avocado toxicosis. Treatment for congestive heart failure (eg, diuretics, antiarrhythmic drugs) may be of benefit but may not be economically feasible in production animals.
Birds and livestock exposed to avocado plants or fruits are at greatest risk of avocado toxicosis.
Myocardial injury can be extensive, especially in birds.
Treatment is supportive and focused on managing clinical signs.