The macadamia tree (Macadamia integrifolia Maiden & Betche, Macadamia ternifolia F. Muell. and Macadamia tetraphylla L.A.S. Johnson) is a tropical and subtropical tree valued for its edible oily nuts (kernels). Culled macadamia nuts, nuts husks and macadamia oil cake resulting from the oil extraction of nuts can be used as animal feeds.
Morphology
Macadamia trees are tropical or subtropical evergreen trees reaching 20 m high. They have a dense, dark green canopy. The leaves are petiolated, borne in pairs, triplets or fours. The leaf blades are oblong, about 30 cm long, dantate. The flowers are borne on long spikes. The fruits are drupes, 2-3 cm in diameter. The external envelop of the fruit is a fleshy green husk. At maturity the fruits are shed from the trees and the husk splits open. Inside, the nut consists in a hard shell and a very oily kernel. High grade quality macadamia nuts must have more than 72% oil (Bittenbender et al., 2011; Duke, 1983).
Uses
Macadamia nuts are mainly used for food. The tasty nuts (kernels), slightly reminding of coconut, can be eaten raw or roasted as snacks. Macadamia nuts are ingredients of confectionery (chocolate-covered nuts), bakery and ice-cream specialties. Macadamia nuts are so relished by rats, wild pigs and cockatoos, that these animals are considered as pests by macadamia producers in Hawaii and Australia (Hamilton et al., 1959; Bittenbender et al., 1990; Tobin et al., 1993; Wilkinson, 2005). The nuts yield valuable oil used in cosmetics (skin and hair care, soaps, shampoos) or as salad or cooking oil. Husks and shells can be mulched for fertilizer. Shells can be used as fuel for nut roasting or as a substitute of sand in sand-blasting process. Macadamia trees can be planted as ornamental or in agroforestry systems (in association with coffee plants or other cash crops) (Bittenbender et al., 2011; Duke, 1983).
Macadamia nuts are mainly produced for human consumption, and are commercialised at a relatively high price. Except for culled nuts, they are thus unlikely to be used profitably for livestock, except perhaps for pets. The oil-rich and sometimes protein-rich macadamia oil cake obtained after oil extraction has potential as a feed ingredient for livestock.