Measurements of nutritive value of a range of tropical legumes and their use in legume evaluation

Abstract

Measurements of leaf and stem quality were taken from 4-10 legumes at 3-5 sites in each of 5 different multi-site experiments grazed by cattle. The sites were in widely separated areas in Queensland, Australia with one site in northern New South Wales. The samples, taken after a period of active growth, were from the terminal 15 cm of shoots of most legumes, although the terminal 30 cm was used for twining legumes like Siratro (Macroptilium atropurpureum). These were taken as a reasonable approximation to the 'grazed layer'. The leaf and stem components were analysed for acid detergent fibre (ADF), N and P; and the % leaf in the sample was calculated. In most sets of samples, there were consistent differences among legumes in the levels of ADF, N and P, the differences usually being greater in the leaves than in the stems. Species with consistently low ADF (ca. 20%) and high N (ca. 4%) in the leaves were Clitoria ternatea, Desmanthus spp., Aeschynomene villosa and Ae. americana whereas other species such as Stylosanthes scabra had consistently higher ADF (ca. 25-30%) and lower N levels (ca. 3%). Levels of ADF in leaf were sometimes half of the levels in new terminal stem. There were also some consistent differences in % leaf in the samples. Stylosanthes scabra and S. seabrana usually had the lowest % leaf. Thus, there were some consistent differences among the rankings of nutrient attributes in different legumes across different sites. However, it is argued that the impact of these differences on animal production will often be over-ridden by the proportions and amounts of legume leaf and stem ingested and that measurements of nutritive value should not be given priority in early stage evaluation studies. Levels of Na, K, Ca, S, Mg, Cu, Zn and Mo were also measured in most samples. The main differences were the high levels of Na (1000-1800 mg/kg) in S. scabra cv. Seca and Indigofera schimperi, which were about 10 times those in the other species.