POTENTIAL AVERSIVE COMPOUNDS IN LEAFY SPURGE FOR RUMINANTS AND RATS

Several wild and domestic ruminant species and horses apparently will not consume leafy spurge (Euphorbia esula) while grazing range and pas ture lands. It has been demonstrated that leafy spurge can elicit cond itioned food aversions in cattle and sheep, and the aversion-eliciting capacity of leafy spurge may account for why cattle seldom graze this nutritious plant and why sheep may not readily consume it at some loc ations. The identity of the aversive compound(s) in leafy spurge is un known, but several different diterpenoid ingenol esters have been isol ated from its tissues, and we suspect that one or more ingenol esters may be aversion-eliciting compounds in leafy spurge. The objectives of this study were to determine whether or not leafy spurge is aversive to laboratory rats and if a crude acetone extract of leafy spurge, pre sumably containing ingenol esters and other phytochemicals, could gene rate an aversive response in sheep and laboratory rats. An additional objective was to determine whether or not a particular ingenol monoben zoate, which may be similar to ingenol esters in leafy spurge, might a lso elicit an aversive response from rats. Rats exhibited food aversio ns associated with leafy spurge (P < 0.05). An acetone extract of leaf y spurge induced conditioned food aversions in both sheep and rats (P < 0.01). The ingenol 3-monobenzoate also induced conditioned food aver sions in rats (P < 0.01). Our interpretation of these data is that mts can be used as a model for cattle and sheep with respect to their ave rsion to leafy spurge ingestion. Additionally, we suggest that one or more ingenol esters may be aversion-inducing agents in leafy spurge. H owever, others may exist in leafy spurge that are also aversive or are the only or prime aversive chemicals.