Nutritive Value of Macadamia Nut Husks in Ruminant Rations
A 1970 Hawaii Agricultural Experiment Station report examined ground macadamia nut husks as an ingredient in sheep rations. Researchers assessed feed acceptance, nutrient digestibility and nitrogen retention when husks replaced conventional ration ingredients. A separate trial with yearling lambs found lower weight gain as the husk proportion increased. Although sheep accepted the diets, higher inclusion levels were associated with poorer nutrient utilization and growth.
What the study did and found
Campbell, Nolan and Lee (1970) studied crossbred wethers averaging 142 lb liveweight. Ground macadamia husks made up 12%, 24% or 36% of tested rations, replacing cracked maize and barley in concentrate diets or pangola grass in roughage diets.
The sheep accepted the husk-containing feed, but nutrient digestibility generally declined as inclusion increased. Ether extract in roughage diets was the reported exception. Nitrogen retention also fell, and yearling lambs gained less weight at higher husk levels.
Why it is cited
The study distinguishes palatability from nutritional value: animals may consume a feed ingredient readily without utilizing its nutrients efficiently. Its graded feeding design also compared husks replacing grain ingredients with husks replacing forage.
The report became an early example of evaluating agricultural processing residues through digestibility, nitrogen balance and growth, rather than feed acceptance alone.
The 1970 findings support a directional association between increasing ground-husk inclusion and poorer nutritional performance in the tested sheep diets. Individual digestibility coefficients, detailed nitrogen-balance values, sample sizes and daily weight-gain figures are not presented in this archive record. The results concern ground outer husks, not every macadamia co-product. Feed-grade nuts and oil cake differ in composition and processing, so their feeding outcomes cannot be inferred directly from this experiment. |
The topic today
Agricultural residues remain subjects of livestock-feed research, but their value depends on composition, processing and the ingredient being replaced. Fiber content, nutrient availability and variability between batches can affect animal performance.
The historical trial remains useful as a reminder that acceptable palatability is not sufficient evidence of nutritional suitability. Modern evaluations must distinguish macadamia husks from nuts, oil cake and other processing residues.