Effect of amount offered on intake, digestibility and value of Gliricidia sepium and Leucaena leucocephala for West African Dwarf goats
Bosman, H.G.; Versteegden, C.J.G.M.; Odeyinka, S.M.; Tolkamp, B.J.
Small Ruminant Research 15(3): 247-256
In two experiments with Gliricidia sepium (G) and G combined with Leucaena leucocephala (GL), 14 West African Dwarf goats were offered seven feed levels varying from 60 to 120 g DM kg-0.75 d-1, with increments of 10 g, in Expt. 1, and from 40 to 130 g DM kg-0.75 d-1, with increments of 15 g in Expt. 2. Maximum DMI for the G and GL were, in Expt. 1: 72.5 +- 2.6 and 90.7 +- 27.2, in Expt. 2: 55.5 +- 3.7 and 63.4 +- 5.3 g kg-0.75 d-1, respectively. In both experiments GL rations were more digestible than G rations, the difference in the second experiment being larger (10.3 vs. 3.6 percentage units), mainly due to a lower digestibility of G. A marked effect of refusal rate on intake was found and the relationship between refusal rate and DMI differed per diet. Animal production per unit of forage offered was maximal at offer levels ranging from 79.4 (Expt. 1, G) to 106.6 g DM kg-0.75 d-1 (Expt. 1, GL). Corresponding weight gains were estimated to range from 2.0 (G2) to 8.2 g kg-0.75 d-1 (GL1). Refusal rates at maximum production levels varied from 13.4% (G1) to 41.6% (G2). Estimated maintenance levels were attained at refusal rates varying from 0.7% (G1) to 20.3% (G2). It was concluded that a wide range of offer levels is required to obtain a reliable estimate of the relationship between feed offer and intake. Feeding at a fixed refusal rate to determine the quality of feeds may lead to misjudgment as feeds do not attain maximum intake at the same refusal rate. If a feed is heterogeneous and thus offers opportunity for selection, high offer levels and accompanying high refusal rates may have to be accepted if the objective is to maximise animal production per unit of available feed.