Macadamia species: Macadamia nut

Family

Protaceae

Common Name

Macadamia nut, Queensland nut (Macadamia integrifolia), and rough shell macadamia or bopple nut (M. tetraphylla).

Plant Description

A relatively small genus of 11 species of medium sized trees native to Australia, Caledonia, and Indonesia that are commonly grown commercially in Hawaii and California. As evergreen rain forest trees, they have evergreen, leathery, lanceolate, serrated or entire, leaves arranged in whorls of 3 - 4 on the twigs. Inflorescences consist of many small white to pinkish flowers crowded on pendent cylindrical spikes. The fruits are nuts which take up to 9 months to mature. The edible nuts are encased in a tough endocarp or shell that must be cracked to access the fruit (Fig. 261 and Fig. 262).

Figure 261. Macadamia integrifolia.

Figure 262. Macadamia nuts (shelled).

Toxic Principle and Mechanism of Action

The toxin in macadamia nuts responsible for causing poisoning in dogs has not been identified. The mean dose of the nuts that will cause poisoning is 11.7 mg/kg body weight, with signs of intoxication appearing in less than 12 hours of consuming the nuts [1]. Dogs experimentally dosed with 20 gm macadamia nuts/kg body weight orally developed signs of poisoning within 12 hours, and exhibited weakness, inability to rise, central nervous system depression, vomiting, and hyperthermia with rectal temperatures up to 45.5°C [1]. Recovery occurs in 24 hours.

Macadamia nuts contain significant quantities of palmitoleic acid, oleic acid, linoleic acid, and linolenic acid [2]. In addition there are significant amounts of alpha-tocopherol and various other sterols. Similar profiles of monounsaturated fatty acids are found in almonds, peanuts, hazel nuts, and walnuts [2].

Risk Assessment

Dogs are unlikely to be affected by the nuts that may fall from the tree as the nuts are too tough for dogs to break open. Most poisonings occur when a dog is fed the shelled nuts or eats cookies made with macadamia nuts.

Clinical Signs

Within 12 hours of eating the nuts, dogs develop weakness, ataxia, depression, vomiting, muscle tremors, stiffness, lameness, inability to rise, and hyperthermia [1]. Elevated serum alkaline phosphatase, triglyceride and lipase levels may be elevated, returning to normal in 48 hours [1]. Treatment is seldom necessary as dogs recover in about 24 hours.