Sweet Potato Leaves for Growing Pigs: Biomass Yield, Digestion and Nutritive Value

An, L.V., 2004. Sweet potato leaves for growing pigs: Biomass yield, digestion and nutritive value. Doctor's dissertation. ISSN 1401-6249, ISBN 91-576-6750-0 The aim of the present studies was to evaluate the potential of using sweet potato leaves (Ipomoea batatas (L.) Lam) as a protein source in diets for growing pigs. A number of sweet potato varieties were evaluated with respect to the biomass yield of the leaves, stems and tubers under different leaf harvesting intervals and defoliation techniques with the aim of selecting the best varieties for forage production. The biomass yields of leaves, stems and tubers were found to vary according to variety, season and defoliation technique. The best options in terms of leaf and stem production were a cutting interval of 20 days and a defoliation of 50% of the total branches. Defoliation reduced tuber production. Sweet potato leaves (SPL) had a crude protein (CP) content of 25.5-29.8% in dry matter, which was markedly higher than in the stems. The leaves can be preserved as feed for pigs by ensiling with either cassava root meal, sweet potato root meal or sugarcane molasses as additives. The optimum level of additive is 60 g kg-1 of the wilted sweet potato leaves. The digestibility in growing pigs of dry matter, organic matter (OM) and CP of ensiled sweet potato leaves was high, but that of crude fibre was low. Sweet potato leaves can be used for feeding pigs in fresh, dry and ensiled forms. The total tract and ileal digestibility values of CP, OM and neutral detergent fibre (NDF), and ileal digestibility of amino acids were not different among fresh, dry and ensiled sweet potato leaves. The mean ileal and total tract digestibility of the CP of sweet potato leaves was 74% and 76%, respectively. Sweet potato leaves are high in protein content compared to other protein-rich forages. Lysine is the first limiting amino acid. Growing pigs fed sweet potato leaves with addition of synthetic lysine had daily live-weight gains of 536 g day-1, which was similar to that of pigs fed a control diet with fish meal as the protein source (542 g day-1). However, without addition of lysine to the SPL diet daily live-weight gain was only 482 g day-1. It is concluded that SPL can be considered as a potentially valuable protein source for pigs. The leaves can be used fresh, dried or as silage, and can replace fish meal and groundnut cake as a protein source for growing pigs under small farm conditions in central Vietnam.