Influence of season/year and species on chemical composition and in vitro digestibility of five Indigofera accessions

Two experiments were completed to determine the influence of season/year and species on forage quality of Indigofera accessions. In Experiment 1, leaf material was collected from five Indigofera species (i.e., I. amorphoides, I. arrecta, I. brevicalyx, I. costata and I. cryptantha) by harvesting six middle plants of a plot in the autumn of 2003 and the autumn of 2004. In Experiment 2, edible forage (leaves + <3 mm stems) material were collected by harvesting six middle plants in the autumn of 2004 and the spring of 2004. Both leaf meal and edible forage material were analyzed for dry matter (DM), ash, crude protein (CP), neutral detergent fibre (NDF), in vitro digestible organic matter (IVDOM), as well as Ca, P, Mg, Cu, Zn and Mn concentrations. In Experiment 1, the interaction effects occurred between species and year of cutting (P<0.05) in studied parameters except Cu concentration. In Experiment 2, interactions (P<0.05) occurred between species and season effect for ash content as well as Ca and Mg concentrations in the edible material. The CP content of the leaf meal ranged between 223 and 311 g/kg DM and that of edible forage material between 81 and 287 g/kg DM. Spring growth had a higher (P<0.05) CP content than autumn growth in all species. The NDF content of leaves ranged between 189 g/kg DM in I. amorphoides and 504 g/kg DM in I. costata, and that in edible material ranged between 328 g/kg DM in I. arrecta and 654 g/kg DM in I. cryptantha. The in vitro OM digestibility of leaves ranged between 568 g/kg DM in I. cryptantha and 717 g/kg DM in I. amorphoides, while that of edible material ranged between 507 and 722 g/kg DM in I. cryptantha. In contrast to the trend with CP and NDF, in vitro OM digestibility of dry material tended to decrease from the spring of 2004 to the autumn of 2004 harvest. Higher levels of Ca, P, Mg, Zn and Cu occurred in the leaf meal of the first harvest than in the re-growth harvest. All of the species had Ca, Mg, Zn and Mn levels that could meet the requirements of ruminants, but P and Cu were slightly deficient for some of the species in the autumn harvest, making it essential to supplement P and Cu from other sources during this period to meet animal requirements.