Nutritional characterization of some tropical urban market crop wastes

Market crop wastes of banana (Musa acuminata) leaves and pseudo-stem sheaths, sweet potato (Ipomoea batatas) vines and Solanum aethiopicum (traditionally known as nakati) were collected from three major markets in Kampala (Uganda). The wastes were evaluated for chemical composition during the dry and wet seasons, rumen degradation using three cannulated indigenous mature ewes, and digestibility using 12 indigenous intact growing male goats, 4–6 months old and weighing 15.8 kg (S.D. 2.1). The goats in the digestibility study were kept in metabolism cages and fed the wastes as sole diets, either fresh or wilted.

Mean dry matter (DM) content was 97, 121, 197 and 216 g/kg for pseudo-stem sheaths, nakati, sweet potato vines and banana leaves, respectively. Crude protein (CP) was 34, 109, 112 and 114 g/kg DM for pseudo-stem sheaths, banana leaves, sweet potato vines and nakati, respectively. The chemical composition was similar among seasons and markets for the banana based wastes. However, for sweet potato vines and nakati, the wet season wastes had significantly higher CP and lower NDFom and ADFom. Chemical composition was different (P<0.05) among the markets for nakati. Effective degradability differed (P<0.05) between the wastes, averaging 0.43 (banana leaves), 0.47 (pseudo-stem sheaths) and 0.56 (nakati) to 0.69 g/g DM incubated (sweet potato vines). DM intake, N retention and digestibility were not significantly affected by wilting. Average DM intake was 176, 270 and 559 g/day; CP intake was 26, 30 and 63 g/day, while metabolizable energy (ME) intake was 1.3, 1.7 and 5.1 MJ/day for nakati, banana leaves and sweet potato vines, respectively. N retention (as a fraction of N intake) was −0.51 (banana leaves), 0.62 (nakati) and 0.39 (sweet potato vines). The organic matter (OM) and CP digestibilities of banana leaves were low, averaging 0.52 and 0.49, respectively. The high moisture content of nakati wastes resulted in low intake, whereas banana leaves had a low degradation rate and a low N retention. Market sweet potato vine wastes were sufficient to provide the CP and ME required by growing goats under tropical conditions.