Effect of previous locoweed (Astragalus and Oxytropis species) intoxication on conditioned taste aversions in horses and sheep

Authors: Pfister, James; Stegelmeier, Bryan; CHENEY, CARL - UTAH STATE UNIVERSITY; Gardner, Dale

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2007
Publication Date: 4/1/2007
Citation: Pfister, J.A., Stegelmeier, B.L., Cheney, C.D., Gardner, D.R. 2007. Effect of previous locoweed (Astragalus and Oxytropis species) intoxication on conditioned taste aversions in horses and sheep. Journal of Animal Science. 85:1836-1841

Interpretive Summary: Locoweed species are a serious toxic plant problem for grazing livestock. Horses and sheep have been conditioned to avoid grazing locoweed using the aversive agent lithium chloride (LiCl). LiCl given by mouth causes gastrointestinal upset. The objective of this study was to determine if previous locoweed poisoning affects food aversion learning in horses and sheep. Horses and sheep were divided into 3 treatment groups: Controls, not fed locoweed and not averted to a novel food; Locoweed-Averted, fed locoweed and averted to a novel food; and Averted, not fed locoweed and averted to a novel food. Animals in the Locoweed-Averted groups were fed locoweed during 2 periods of 21 and 14 days, respectively, with each feeding period followed by a 14 day recovery period. Animals were averted to a novel food at the end of the first locoweed-feeding period, and periodically tested for strength and persistence of the aversion. During the first recovery period, Locoweed-Averted horses ate less (9.5%) of the test food than did Control horses (99.8%), and the Averted horses ate none (0%). During recovery period 2, Locoweed-Averted horses (4.3± 5.7%) differed in consumption of the test food from both the Controls (100%) and the Averted group (0%). Locoweed-Averted sheep differed from Controls (14.4% vs. 99.5%, respectively during recovery period 1), whereas Locoweed-Averted sheep did not differ from Averted sheep (0.6%). During the second recovery period, Control sheep (100%) differed from both Averted (0%) and Locoweed-Averted (12.2%) groups. Two intoxicated sheep (Locoweed-Averted) partially extinguished the aversion during the first recovery period, but an additional dose of LiCl essentially restored the aversion. Two of 3 intoxicated horses had strong aversions that persisted without extinction; one horse in the Locoweed-Averted group had a weaker aversion. These findings suggest that previously intoxicated horses and sheep can form strong and persistent aversions to a novel food, but in some animals, those aversions may not be as strong as in animals that were never intoxicated.

Technical Abstract: Locoweed species (Astragalus and Oxytropis spp.) are a serious toxic plant problem for grazing livestock. Horses and sheep have been conditioned to avoid grazing locoweed using the aversive agent LiCl. The objective of this study was to determine if previous locoweed intoxication affects food aversion learning in horses and sheep. Horses and sheep were divided into 3 treatment groups: Controls, not fed locoweed and not averted to a novel food; Locoweed-Averted, fed locoweed and averted to a novel food; and Averted, not fed locoweed and averted to a novel food. Animals in the Locoweed-Averted groups were fed locoweed during 2 periods of 21 and 14 days, respectively, with each feeding period followed by a 14 day recovery period. Animals were averted to a novel food at the end of the first locoweed-feeding period, and periodically tested for strength and persistence of the aversion. During the first recovery period, Locoweed-Averted horses ate less (9.5 ±5.4%) of the test food than did Control horses (99.8±0.3%), and did not generally differ from Averted horses (0%). During recovery period 2, Locoweed-Averted horses (4.3± 5.7%) differed (P=0.0001) in consumption of the test food from both the Controls (100%) and the Averted group (0%). Locoweed-Averted sheep differed from Controls (14.4±8.4% vs. 99.5± 0.4%, respectively during recovery period 1), whereas Locoweed-Averted sheep did not differ (P > 0.5) from Averted sheep (0.6±0.3%). During the second recovery period, Control sheep (100%) differed (P < 0.05) from both Averted (0%) and Locoweed-Averted (12.2±8.3%) groups. Two intoxicated sheep (Locoweed-Averted) partially extinguished the aversion during the first recovery period, but an additional dose of LiCl essentially restored the aversion. Two of 3 intoxicated horses had strong aversions that persisted without extinction; one horse in the Locoweed-Averted group had a weaker aversion. These findings suggest that previously intoxicated horses and sheep can form strong and persistent aversions to a novel food, but in some animals, those aversions may not be as strong as in animals that were never intoxicated.