Creating aversion to giant fennel ( Ferula communis) in weaned orphaned lambs

Abstract

The circum-Mediterranean perennial Ferula communis (giant fennel) contains anticoagulant constituents and is the most widespread toxic plant in Israel. Most casualties are ewe–lambs at the onset of their first grazing season. We studied the feasibility of implementing conditioned food aversion (CFA) to F. communis in 2-month-old orphaned ewe–lambs recently weaned from an artificial milk dispenser. A procedure of CFA against vetch hay was first elaborated, using a single dose of LiCl administered by drug pistol simultaneously with first-time feeding of vetch hay. The persistence of aversions was evaluated at days 3, 6, 9 and 16 post-dosing. A dosage of 133-mg LiCl kg −1 BW was ineffective in creating aversion. Aversions created by doses of 266- and 400-mg LiCl kg −1 BW persisted 3 and 9 days, respectively. In an experiment aimed at lengthening the persistence of aversion to vetch hay, it appeared that: (i) persistence of 16 days could be achieved by using a double dosing procedure with a 3-day interval between doses; (ii) 400-mg LiCl kg −1 BW was lethal to 7/10 lambs; and (iii) there may be an interaction between post-weaning learning of solid food ingestion and the CFA procedure. In a third experiment, six lambs, which had been accustomed to F. communis for 1 week, were averted to F. communis by administrating two doses of 266-mg LiCl kg −1 BW at 3-day intervals at the time of F. communis meals; six lambs served as unaverted controls and four lambs were averted to vetch hay. Aversion to F. communis and vetch hay persisted for 31 and 16 days, respectively, in lambs kept in individual cages. The lambs were then turned out to pasture on a F. communis-infested artificially-constructed paddock divided into two plots differing in standing biomass of Italian ryegrass. Lambs averted against F. communis consumed 28% less F. communis than unaverted counterparts. The aversion persisted 46 days after first LiCl administration. Lambs consumed more F. communis and CFA was more effective when pasture standing biomass was low (1060 kg DM ha −1), compared with medium (2070 kg DM ha −1). We conclude that: (i) averting young `orphaned' weaned lambs to F. communis is feasible; (ii) LiCl may be lethal to young lambs and the procedure used to avert them to F. communis may interact with post-weaning growth check; and (iii) the effectiveness of aversion is affected by the condition of the F. communis-infested paddock in which lambs are to be grazed.