Conditioned aversion to minimize Ferula communis intake by orphaned lambs

Abstract

The circum-Mediterranean perennial Ferula communis L.(giant fennel) has anticoagulant constituents. Mortality from poisoning can affect 5% of the sheep grazed in infested areas and most casualties are ewe-lambs at the onset of the grazing season. In intensive sheep production systems, ewe-lambs are “orphaned”, artificially reared, and have no opportunity to acquire safe dietary habits by imitating their mothers. The aim of the present study was to evaluate the intake of F. communis in such lambs and to assess the potential of using conditioned aversion as a managerial tool to decrease the frequency of F. communis poisoning. Six lambs weighing approximately 28 kg were averted to F. communis using 2 administrations of 4g LiClin aqueous solution, given immediately after a meal of F. communis; 6 similar lambs served as unaverted controls. The intake of F. communis and the persistence of aversion were assessed over 7 observation days using a simulation of an infested field where freshly cut bunches of F. communis were tied to stakes at 10-m intervals in ryegrass (Lolium multiflorum Lam.) paddocks at the late vegetative stage. Averted lambs grazed separately from unaverted counterparts. Time spent by lambs foraging on F. communis was in the range of 0–0.015 min/hour (not significantly different from nil) in averted, and 0.15–0.24 min/hour inunaverted lambs, respectively (P = 0.002). Consequently, the rate of disappearance of F. communis was greater when grazing was by unaverted than averted lambs (0.29 and 0.15 g/min, P =0.01). The aversion persisted for 25 days after the LiCl treatment, at which time observations were discontinued. Assuming that the amount of F. communis that disappeared is close to actual intake by lambs, intake by unaverted lambs was high enough to endanger the lambs, whereas averted lambs consumed safe amounts of the poisonous plant. It is concluded that conditioned aversion has the potential to alleviate the problem of F. communis poisoning in orphaned ewe-lambs.