Replacement value of tree legumes for concentrates in forage-based diets. II. Replacement value of Leucaena leucocephala and Gliricidia sepium for lactating goats

Laboratory, digestion and lactation trials investigated the replacement value of the tree legumes Gliricidia sepium and Leucaena leucocephala for a concentrate supplement in kinggrass (Pennisetum purpureum) based diets. In the lactation trial, 15 does in mid-lactation were allocated to three dietary treatments in a 3 × 3 Latin square design with five square replications. In the digestion trial, six intact yearling male goats were assigned to the same treatments in a replicated 3 × 3 Latin 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 concentrate. In the legume-supplemented diets, gliricidia or leucaena replaced approximately 50% of the N supplied by the concentrate. Dried banana fruit (Musa×paradisiaca) was used in the legume-supplemented diets to equal the energy content of the control diet. Diets contained approximately 2.2% N and 73% total digestible nutrients. Legumes were greater in total N concentration than kinggrass, with leucaena containing more N than gliricidia (P<0.05). Size and degradation rate of the potentially 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 the legumes than for kinggrass, but the extent of in vitro cell wall digestion was greater (P<0.05) for kinggrass than for the legumes. In vitro OM and cell wall digestion was greatest (P<0.05) for banana. In the digestion trial, apparent dietary OM and cell wall digestibilities were similar (P>0.10) across treatments. Fecal N production was greater (P<0.05) for legume-supplemented diets than the control, leading to lower (P<0.05) N digestibility for legume-supplemented diets. In the lactation trial, OM intake was greatest (P<0.01) for the control diet and least (P<0.01) for the gliricidia-supplemented diet, but milk production characteristics were similar (P>0.10) for all treatments. For iso-energetic diets, up to 50% of the concentrate N may be replaced by the tropical tree legumes gliricidia and leucaena without a reduction in milk production.