MINERAL-COMPOSITION OF TROPICAL FORAGES IN THE MOUNT-ELGON REGION OF KENYA .2. TRACE-ELEMENTS

A survey of trace mineral concentrations in herbage in the Mt Elgon re gion of western Kenya is described. A total of 135 samples of mature h erbage from 84 farms covering 30 000 km(2) was analysed for cobalt (Co ), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), selenium, (Se), and zinc (Zn). Mean (+/-standard deviation) concentrations [mg k g(-1) dry matter (DM)] were Co, 0.2 (0.16); Cu, 4.0 (1.6); Fe, 300 (16 9); Mn, 220 (128); Mo, 1.1 (0.23); Se, 0.1 (0.03); Zn, 23.6 (9.4). Cop per and Zn concentrations were low compared with surveys in other trop ical countries but this may partly reflect the mature stage at which h erbage was sampled. Comparisons with recent estimates of the mineral r equirements of ruminants indicated that most of the samples were defic ient in Cu. A minority of the pastures contained less Se and Zn than r uminants are thought to require, but deficiencies of Co, Fe, and Mn we re rare. Iron may be more significant as an antagonist of Cu but Mo ra rely reached concentrations high enough to be antagonistic to Cu. The possibility of constraints upon livestock production should be investi gated by supplementation trials with grazing livestock beginning with Cu.