Diet selection by domestic goats in relation to blackbrush twig chemistry.
Abstract
The production of current season growth by Coleogyne ramosissima was determined by length measurement in Sept. when the twigs were dormant. Percentage utilization of terminal and basal branches was recorded for 50 plants using a regression approach that predicted twig lengths available before Jan. and in mid-March after browsing by goats. The proportion of leaves and stems in the diet was estimated from analysis of fistula extrusa; a high leaf:stem ratio indicated a greater proportion of basal twigs. Leaf:stem ratios declined during the browsing period as a result of decreased availability of basal twigs, a trend paralleled by dietary CP levels. On lightly stocked pasture leaf:stem ratios were low and increased during the last 3 weeks of study through increased consumption of basal twigs. In vitro DOM values and tannin conc. were also higher for animals browsing the heavily stocked pasture because they consumed a higher proportion of current season growth, while weight losses were lower than on lightly stocked pasture.