Chemical Composition, <i>in situ</i> Degradability and <i>in vitro</i> Gas Production of Tagasaste (<i>Chamaecytisus palmensis</i>) Forage Harvested at Different Stages

Abstract

The leguminous tree tagasaste is highly productive in the Ethiopian highlands. However, its nutritional value, as affected by the different agronomic practices is not fully understood under the tropical highland conditions. This study investigated the quality profile of tagasaste forage harvested at different re-growth stages by measuring the chemical composition, in situ degradability and in vitro gas production. Tagasaste re-growths after one year of establishment was harvested and the re-growths starting from the main rainy season (July) was harvested at 4, 6, 8 and 10 months. The harvested forages were fractionated into leaves and edible branches. Chemical composition, in situ degradability using rumen fistulated steers and in vitro gas production using rumen fluid from rumen fistulated dry cows were evaluated. The average crude protein (CP) content of tagasaste in the leaves ranged between 189 and 242 g kg^-1 dry matter (DM) was not significantly affected by harvesting stage regrowth. The neutral detergent fibre, acid detergent fibre, acid detergent lignin and ether extract contents of tagasaste increased with length of re-growth. The amino acid profile of tagasaste protein showed high contents of the essential amino acids leucine and lysine but lower contents of methionine and histidine. Tagasaste grown under Ethiopian highland conditions was found deficient in phosphorus, sulphur, and sodium, but had adequate amounts of calcium, potassium, zinc and iron. The average in situ potential and effective degradability of leaves were 795 and 518 g kg^-1 DM respectively and was lowest at the 10 months harvesting stage. The in vitro gas production declined with length of re-growth. Gas production was higher for leaves followed by branches with mean value of 43.7 and 39.1 ml 200^-1 mg DM at 24 h respectively. The high CP content, degradability and in vitro gas production of tagasaste forage reveals its high potential to be used as a protein supplement for ruminants. The studied quality parameters should be further verified using animal performance.