Feeding cassava foliage to sheep : nutrient properties and hydrogen cyanide toxicity

Abstract: The potential of cassava foliage (Manihot esculenta Crantz) as a protein-rich feed in sheep production in Vietnam was examined by studying cassava foliage yield, hydrogen cyanide (HCN) content, toxicity and performance of lambs fed the foliage as a supplement. Cassava foliage fed ad libitum as a protein supplement to a basal diet of urea-treated rice straw gave similar lamb live weight gain (LWG) as diets supplemented with commercial concentrate or protein-rich foliage of stylosanthes (Stylosanthes guianensis) or jackfruit (Artocarpus heterophyllus). Field studies showed that higher harvesting frequency gave higher yield of cassava foliage. A K94 cassava variety always gave the highest foliage yield. Content of dry matter (DM), neutral detergent fibre (NDF), acid detergent fibre (ADF) and total tannins in the cassava foliage increased with plant and leaf maturation, while crude protein (CP) and HCN content decreased. Total tannin content was highest at first harvest and decreased slightly at subsequent harvests, while the reverse was true for HCN content. Different cassava varieties and degrees of processing (fresh, wilted or hay) resulted in differences in foliage HCN content. Feeding cassava foliage at 2% of body weight (BW) from the start led to wasted feed, but prolonging the adaptation period to 21 days resulted in lower LWG. A 7-day period for adaptation to cassava foliage was a good compromise for lamb performance and health. Feeding cassava foliage as fresh, wilted or hay did not result in any difference in LWG, but hay had lower DM and CP digestibility. Inclusion of cassava in the diet of sheep had a positive nematode control effect, but HCN consumption and thiocyanate concentration in urine increased with increasing foliage intake.