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.
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, and colic have been reported in horses ingesting avocado fruit and/or leaves.
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 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 (eg, infectious) and other myocardial disorders, including ionophore toxicosis, yew toxicosis, vitamin E/selenium deficiency, gossypol toxicosis, cardiac glycoside toxicosis (eg, oleander), cardiomyopathy, and infectious myocarditis.