Nutritive value of tropical forage plants fed to pigs in the Western provinces of the Democratic Republic of the Congo

The nutritive value of 20 forage plants commonly used for feeding pigs in the Democratic Republic of the Congo was studied to determine chemical composition, protein amino acid profiles, mineral content, and in vitro digestibility using a two-step method combining an enzymatic pepsin and pancreatin hydrolysis followed by a 72 h gas-test fermentation. The highest protein contents (270–320 g/kg DM) were obtained for Vigna unguiculata, Psophocarpus scandens, Leucaena leucocephala, Manihot esculenta, and Moringa oleifera. Grasses, Acacia mangium, and Eichhornia crassipes, showed the lowest crude protein (CP) and highest NDF contents. Cajanus cajan and Trypsacum andersonii had the most balanced amino acid profile, being deficient in lysine and slightly deficient in histidine, while Megathyrsus maximus displayed the highest number of essential amino acids deficiencies. High mineral contents were obtained from, in ascending order, with M. oleifera, V. unguiculata, E. crassipes, Ipomea batatas and Amaranthus hybridus. In vitro dry matter digestibility ranged from 0.25 to 0.52, in vitro CP digestibility from 0.23 to 0.80, in vitro energy digestibility from 0.23 to 0.52. M. esculenta, M. oleifera, I. batatas, Mucuna pruriens, V. unguiculata, P. scandens and A. hybridus showed high digestibilities for all nutrients. Gas production during fermentation of the pepsin and pancreatin-indigestible fraction of the plants varied from 42 ml/g DM for A. mangium to 202 ml/g DM for I. batatas (P<0.001). Short-chain fatty acid production during fermentation varied from 157 to 405 mg/g of the pepsin and pancreatin indigestible fraction. It is concluded that some of these species are interesting sources of proteins and minerals with a good digestibility that might be used more economically than concentrate, especially in smallholder production systems, to improve pig feeding, mineral intake and intestinal health in pigs reared in the tropics.