Biofortified fodder - an environmentally sustainable mechanism to supplement livestock with trace elements?

New Zealand agriculture utilises trace element supplements to protect livestock from fungal infection. For example Zinc (as zinc oxide) administered as an oral drench or intraruminal bolus, is used extensively to protect sheep and cattle from facial eczema. A large percentage of administered Zn is however excreted in faeces and there is published evidence to show that Zn levels in pastoral soils are increasing with time. The long-term environmental affect of this ongoing Zn input to soil is unknown. In this paper we describe research into the efficacy of fodder with an elevated Zn concentration as a potential prophylaxis against facial eczema in sheep relative to a conventional drench. Our hypothesis is that Zn protection afforded by biofortified fodder may be realised at a relatively lower dose, thus limiting transfer of Zn into the pastoral environment. This may represent a more environmental sustainable mechanism to supplement livestock with trace elements than conventional options. Our mechanism of Zn administration can be described as the biofortification of food with essential trace elements. During a controlled feeding trial, 20 sheep were administered one of four Zn treatments over seven days (conventional drench or biofortified / non-biofortified fodder). Blood and faecal samples were taken regularly and analysed for the constituent Zn concentration. Prescribed threshold levels for Zn in blood serum and faeces were used to gauge the likely effect of treatments in protecting against facial eczema. Both conventional ZnO drench and biofortified fodder (willow) increased the Zn concentration in blood and faeces. The drench increased serum levels to above the threshold level for protection, however Zn was rapidly excreted, and after a very short time levels had dropped to below the prescribed concentration. In comparison, serum and faeces Zn levels in the animals fed biofortified willow increased throughout the feeding period. The total amount of Zn administered to animals via willow was significantly lower than that administered via drench, and consequently serum and faeces concentrations did not increase above the prescribed threshold level. However, our results do show that biofortification has potential as a mechanism to deliver trace elements to animals.