Effect of the inclusion of tropical tree legumes, Gliricidia sepium and Leucaena leucocephala, on the nutritive value of silages prepared from tropical grasses

Abstract

SUMMARYSilages were prepared from the tropical grasses, pangola grass (Digitaria decumbens) and setaria (Setaria sphacelata), with the addition of molasses (4% w/w) and/or leaves (33%) from the leguminous trees leucaena (Leucaena leucocephala) and gliricidia (Gliricidia sepium). All forages were grown at the University of Queensland farm in south eastern Queensland during 1985. These silages, together with hays made from these grasses and sorghum silage (13 diets) were fed to sheep to assess their nutritive value. All silages were well preserved, as indicated by low pH (3·5–4·4), low ammonia N (26–57 g/kg total N) and high lactic acid (73–95% total acids) contents. The addition of legumes increased both the dry matter (DM) and total N (TN) contents of silages to the same extent as the addition of both legumes and molasses at ensiling. Sheep given silages prepared from pangola grass and legumes (±molasses) consumed similar DM intakes (22·9–25·4 g/kg0·75 per day) as sheep given pangola grass hay (23·9 g/kg0'75 per day). Silage made from pangola grass + molasses was of low palatability (16·1 g/kg0·75 per day). The digestibilities of silage DM (DMD) and its fibrous components were significantly (P<0·05) lower (DMD 53·3–60·6%) than that of pangola hay (DMD 64·7%). Silages and hay made from setaria, and sorghum silage, were of lower nutritive value than those from pangola grass. The addition of leucaena and molasses increased silage DM intakes (21·1 g/kg0·75 per day) above those for setaria hay and setaria + molasses silage (16·7 and 19·0 g/kg0·75 per day respectively). The intakes of silages made from gliricidia (17·1 g/kg0·75 per day) were significantly (P <0·05) improved when molasses was included at ensiling (21·8 g/kg0·75 per day). The digestibilities of silage DM were significantly (P<0·05) higher (DMD 53·6–60·4%) than that of setaria hay (DMD 40·6). Liveweight change in sheep was significantly (P<0·05) correlated with intakes of digestible DM (r2= 0·74) and with N intake (r2= 0·82). The inclusion of legumes in the silages increased N retention and, for setaria silages, also increased rumen ammonia concentration. It was concluded that tropical grasses can be effectively ensiled by the addition of legumes alone and, with the exception of setaria/gliricidia silages, the resultant silages were of sufficiently high quality to merit their use in tropical animal production systems.