Feasibility of in vivo digestibility trials with lactating goats browsing fresh leafy branches

Abstract

In order to obtain a reliable assessment of apparent digestibility of tree foliage for animals with high requirements, a new technique is proposed. Local goats adapted to range browsing were placed in large and comfortable cages, specially designed to suit the particular behavior of goats. In front of the cages, unprocessed fresh, leafy branches, cut no more than 2 h earlier and clamped 3 by 3 on a special “tree-like structure” were distributed continuously during daytime. Goats may, in this way, select and browse the offered forage in conditions as close as possible to those on the rangeland. This foraging method leads to very high and steady intake levels (for digestibility trial periods of 18 days): 90 ± 4 g DMI/kg LW 0.75 with near-maintenance animals browsing plain holm-oak ( Quercus ilex) in April; and 101 ± 6 g DMI/kg LW 0.75 with lactating animals, browsing the same oak, and 250 g DM urea-molasses supplement. Structural composition of intake was measured with a phytoecological range survey method, applied to each distributed branch, i.e. the browsed-class method. Browsing behavior in cages was similar to that measured on rangeland. Goats were able to adjust both choice of branch type and consumption rates of branches to achieve a stable mean bite composition of leaf to stem ratios = 6.0 ± 0.1, corresponding on the range to a 10 animal ha −1 stocking density. In the case of animals browsing fresh branches, the notion of “refused material” must be replaced by “consumption rate” of “Potential Edible Matter”. This consumption rate may be influenced by supplementary feeding and the diversity in palatibility of offered branches. This technique, using lactating animals and branches cut by hand in the forest, appears to be a reliable way of assessing actual use of tree and shrub foliage for animal production. It gave digestibility estimates that varied little between animals, for plain holm-oak D.M.D. = 47.8 ± 1.0%, and soybean-meal supplemented holm-oak D.M.D. = 51.6 ± 9%.