Macro and trace element composition of forages in Western Kenya: Implications for sheep and cattle health and production.

Abstract

In a preliminary study, 135 samples of mature forages from 84 livestock farms (farm size 10 • 6000 acres) in Bungoma and Trans Nzoia districts were assessed for both macro (Co, S, Mg and P) and trace elements (Co, Cu, Se, Mo, Zn, Fe and Mn) using a variety of chemical techniques. Mean concentrations of these elements were low compared with surveys in other tropical countries. Comparison with recent estimates of the mineral requirements of cattle and sheep indicated that 70 -98 % of the forages were deficient in Co, P and Cu. Several pastures contained less Mg, S, Zn andSe than ruminants are thought to require but deficiencies of Co, Mn and Fe were rare. Re-assessment of the data for Cu availability using two derived prediction equations, one for hay: Cu (%DM)=8.9 -0.7logtMo - 2.61logc S and the other for grass: Cu (%DM) = 5.72 - 1.2975 • 2.785hgf Mo + 0.227 Mo X S showed that forage Mo and S rarely reached concentrations high enough to be antagonistic to Cu. However, Fe concentrations were sufficiently high to implicate this element as an independent Cu antagonist. Since forage mineral deficits are not synonymous with constraints upon livestock production, the possibility of such constraints should be further investigated, first through blood analysis and then by supplementation trials with grazing animals beginning with Cu