INDICES OF CASSAVA SAFETY FOR LIVESTOCK FEEDING

Literature on the use of cassava for livestock feeding dates back to 1903 when Tracy reported depression in growth of pigs fed on cassava diets. He attributed the depression to the 'carbonaceous' nature of cassava thus indicating a need for protein supplementation. Subsequent reports of growth depression caused by cassava in livestock failed in most instances to address the need for additional nutrient supplementation, microbial infestation of dried or fermented cassava and cyanogenic potential. Death reported in livestock fed fresh or processed cassava roots or leaves have been sporadic. In most instances, dietary cyanide exposure from cassava has been implicated without determination of amount of cyanogens in the material thus making the evidence circumstantial. The practicability of life cycle feeding of cassava to pigs has been demonstrated and it has been suggested that this can be practiced for other livestock if the cassava based diets are adequately supplemented with sulfur amino acids and the cyanogen content of such rations kept at safe levels.

Growth depression in balanced rations with cyanogen level of 750 mg HCN equivalent kg^-1 has been reported in pigs. Satisfactory performance was however obtained in growing pigs fed on fresh cassava rations containing less than 100 mg HCN equivalent kg^-1. Feeding trials with gestating pigs showed satisfactory performance in terms of litter size, birth and weaning weights on fresh cassava rations containing up to 500 mg HCN equivalent kg^-1. Placental thiocyanate transfer to the fetus however occurred at 500 mg HCN equivalent kg^-1. Milk thiocyanate was also elevated and the thyroid was enlarged at that level. Another trial with growing pigs fed cassava peel based rations containing 96 mg HCN equivalent kg^-1 gave satisfactory growth rate but depressed serum thyroxine.

The safety of cassava for livestock can therefore be guaranteed if the dietary cyanogens level is less than 100 mg HCN equivalent kg^-1, and the rations are adequately supplemented with proteins, particularly the sulfur amino acids, and with iodine. Processing of the cassava should also ensure minimal microbial contamination and feeds should be pelletized to reduce dustiness. The experience of the European Community countries that have succeeded in using imported cassava for livestock feeding for the last two decades with satisfactory performance is enough evidence that cassava can be used in countries that produce an abundance of this root crop, without fear of its toxicity in intensive livestock production systems.