Abstract :
Grazing livestock frequently ingest toxic plants, occasionally with fatal results. Behavioral
adjustments by livestock may reduce toxin intake; for example they can develop food aversions
which may protect animals from over-ingestion of toxic plants. The purpose of this
study was to evaluate three plants with different mechanisms of toxicity for their efficacy
in conditioning a taste aversion: (1) a seleniferous plant, Xylorhiza glabriuscula, (2)
an indolizidine alkaloid-containing plant, Astragalus lentiginosus, and (3) a diterpene acidcontaining
plant, Gutierrezia sarothrae. For each plant species, 15 sheep were divided into
3 treatment groups and periodically tested for consumption of a novel food, whole corn:
(1) controls – given 200 g of ground alfalfa hay by oral gavage, (2) averted – given lithium
chloride (LiCl) at 175 mg/kg BW via oral gavage, and (3) given the specific target plant by
oral gavage. X. glabriuscula was given at a dose equivalent to 3mg Se/kg BW; A. lentiginosus
was given at a dose equivalent to 3 mg/kg of the toxic alkaloid, swainsonine; freshly
thawed G. sarothrae was dosed at 5 g/kg body weight (BW). Both LiCl and Xylorhiza conditioned
an aversion to corn, with sheep eating 1.6 and 0.6% of offered corn during the
final test; controls were not averted, eating 93% of the corn (P < 0.01). Sheep were partially
averted by Xylorhiza after a single dose, and the aversion was complete after the second
dose. Sheep were not averted by A. lentiginosus or G. sarothrae. Of the three toxic plants
used in this study, only Xylorhiza conditioned a taste aversion. These results likely reflect
differing mechanisms of action of the plant toxin(s) on brain and gut structures important
for forming conditioned taste aversions. These results suggest that conditioned aversions to
Se-containing plants may help to deter consumption of such plants by grazing ruminants on
rangelands.
