REPLACEMENT VALUE OF TREE LEGUMES FOR CONCENTRATES IN FORAGE-BASED DIETS .2. REPLACEMENT VALUE OF LEUCAENA-LEUCOCEPHALA AND GLIRICIDIA-SEPIUM FOR LACTATING GOATS

Laboratory, digestion and lactation trials investigated the replacemen t value of the tree legumes Gliricidia sepium and Leucaena leucocephal a for a concentrate supplement in kinggrass (Pennisetum purpureum) bas ed diets. In the lactation trial, 15 does in mid-lactation were alloca ted to three dietary treatments in a 3 X 3 Latin square design with fi ve square replications. In the digestion trial, six intact yearling ma le goats were assigned to the same treatments in a replicated 3 x 3 La tin square design. Diets were based on kinggrass and supplemented with either a commercial concentrate feed, gliricidia or leucaena. In the control diet, 60% of the total dietary N was supplied by the concentra te. In the legume-supplemented diets, gliricidia or leucaena replaced approximately 50% of the N supplied by the concentrate. Dried banana f ruit (Musa x paradisiaca) was used in the legume-supplemented diets to equal the energy content of the control diet. Diets contained approxi mately 2.2% N and 73% total digestible nutrients. Legumes were greater in total N concentration than kinggrass, with leucaena containing mor e N than gliricidia (P<0.05). Size and degradation rate of the potenti ally ruminally degradable N fraction were greatest for gliricidia and least for kinggrass, with values for leucaena being intermediate (P<0. 05). In vitro organic matter (OM) digestion was greater (P<0.05) for t he legumes than for kinggrass, but the extent of in vitro cell wall di gestion was greater (P<0.05) for kinggrass than for the legumes. In vi tro OM and cell wall digestion was greatest (P<0.05) for banana. In th e digestion trial, apparent dietary OM and cell wall digestibilities w ere similar (P>0.10) across treatments. Fecal N production was greater (P<0.05) for legume-supplemented diets than the control. leading to l ower (P<0.05) N digestibility for legume-supplemented diets. In the la ctation trial. OM intake was greatest (P<0.01) for the control diet an d least (P<0.01) for the gliricidia-supplemented diet, but milk produc tion characteristics were similar (P>0.10) for all treatments. For iso -energetic diets, up to 50% of the concentrate N may be replaced by th e tropical tree legumes gliricidia and leucaena without a reduction in milk production.