Nutrient characterisation and in vitro digestibility of grass and legume/browse species - based diets for beef cattle in Vanuatu

Abstract

Some grasses, Buffalo (Panicum Coloratum), Guinea (Panicum maximum), Setaria (Setaria sphacelata), Embu (Panicum maxum), Elephant (Pennisetum Purpureum), Koronivia (Brachiaria humidicola), and Signal (Brachiaria decumben); and legumes/browses Gliricidia sepium, Glycine wightii, Green desmodium and Leucaena leucocephala grazed by beef cattle in Vanuatu were characterized for crude protein (CP), fibre fractions, macro and micro minerals (phosphorus, calcium, magnesium, potassium, copper, iron, manganese and zinc) and energy. Also in vitro digestibility study was carried out to predict the utilization of available nutrients. Data obtained were discussed in light of whether available nutrients would satisfy requirements of grazing beef cattle of different age and physiological function. The CP of grass and legume/browse species ranged from 7.9-17.8% and 10.5-23.9% respectively. L. leucocephala has a higher CP while Green leaf desmodium had the lowest CP content. DM and NDF were higher (P<0.05) in the grasses while CP was higher in the legume/browse species. Organic matter (OM) within and between the grass and legume/browse species varied. Mean concentrations of calcium (Ca) and phosphorus (P) in the grass species was 5.7 g/kg DM and 2.6 g/kg DM, respectively and this resulted in an average Ca:P ratio of 2.2:1 for the grasses while the legume /browse species had Ca:P ratio of 5.3:1. Ca was low while K was high in the grasses compared to the legume/browse species. Among the microminerals Cu was critically low in both the grass and legume/browse species. In vitro DMD, OMD and CPD between and within the grass and legume/browse species were not significantly different (P>0.05) from each other, however NDFD and ADFD were higher (P<0.05) in the grasses than in the legumes/browses. In conclusion, the results of these analyses and the in vitro digestibility study have provided information on nutrients that are adequate and/or inadequate in the grass and legume/browse species components grazed to sustain beef cattle production in Vanuatu. The very low concentration of Cu in both the grass and legume/browse species therefore demonstrates the need to supplement grazing beef cattle with mineral lick blocks to overcome its deficiency.