Trace element imbalance in vegetation as a threat to free ranging cattle in the Gilgel Gibe valley, Ethiopia

摘要

As in many tropical countries, natural pastures are the main source of nutrients for cattle in Ethiopia. However, there is limited information available with regard to trace element concentrations in Ethiopian forages. In this study, 58 plants were sampled in the Gilgel Gibe valley based on the observed ingestion by zebu cattle (Bos indicus) herds, grazing at different elevation and soil types, and analysed for copper (Cu), cobalt (Co), iron (Fe), molybdenum (Mo), manganese (Mn), sulfur (S), selenium(Se) and zinc (Zn). The effect of elevation, soil type and plant type on the above trace element concentrations was investigated. Deficient Cu concentrations were present in 71% of samples. Plant samples contained at least marginally antagonistic concentrations of Mo, S and Fe towards Cu in 36, 48 and 88% of cases respectively, and deficient Se and Zn concentrations in 57 and 45% of cases respectively. For Mn and Zn, plant concentrations differed according to elevation region. Plants on Nitisol-Acrisol-Ferralsol associations contained higher amounts of Fe than on Planosol-Vertisol associations. Concentrations of Cu and S were higher in herbaceous and woody plants than in grasses and crop resides, whereas concentrations of Co were higher in herbaceousthan in other plant types. Differences between plant types were also present for Fe. Overall, micro mineral deficiency is very likely to develop in cattle ranging at the studied area. Plant mineral concentrations were affected by a variety of factors, such as elevation, soil type and plant group, calling for a nuanced assessment of plant survey results.