Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2001
Publication Date: 8/1/2002
Citation: PFISTER, J.A., STEGELMEIER, B.L., CHENEY, C.D., RALPHS, M.H., GARDNER, D.R. CONDITIONED TASTE AVERSIONS TO LOCOWEED (OXYTROPIS SERICEA) IN HORSES. JOURNAL OF ANIMAL SCIENCE. 2002. Interpretive Summary: Consumption of locoweed is a serious problem for horses as they readily eat locoweed, and are very sensitive to the toxic effects. Further, the loss of individual horses to locoweed poisoning exacts a high economic and emotional toll for horse owners. This study investigated the use of aversive conditioning to train horses to not eat locoweed. In aversive conditioning procedures, animals are given the plant simultaneously with a drug that causes gastrointestinal distress such that in future encounters the animal will not eat the plant. Preliminary trials indicated that lithium chloride at 190 mg/kg body weight was the appropriate aversive agent; apomorphine was not effective. Ten horses were conditioned to eat fresh locoweed. Most horses (5/6) were averted to fresh locoweed in pen trials. Controls continued to eat fresh locoweed whenever it was offered. In a 7-day grazing trial, treated horses generally abstained from eating locoweed except for one episode of consumption on day 2. Controls averaged about 9% of their forage intake as locoweed. There are other questions to answer about averting horses to locoweed, but aversive conditioning appears to have potential for reducing locoweed intoxication in horses.
Technical Abstract: Locoweed (Oxytropis sericea) is a serious poisoning problem for horses grazing on infested rangelands in the western U.S. Our objectives were to determine 1) whether lithium chloride (LiCl) or apomorphine (APO) would condition aversions to palatable foods and at what doses, and 2) whether horses could be averted to fresh locoweed in a pen and grazing situation. Apomorphine was not an acceptable aversive agent because at the dose required to condition an aversion (ò0.17 mg/kg BW), APO induced unacceptable behavioral effects. Lithium chloride given via stomach tube at 190 mg/kg BW conditioned strong and persistent aversions to palatable feeds with minor signs of distress. Pen and grazing tests were conducted in Colorado to determine if horses could be averted to fresh locoweed. Pen tests indicated that most horses (5/6) were completely averted from locoweed. Treated horses ate 34 g of fresh locoweed compared to 135 g for rcontrols (P<0.01) during three pen tests when offered 150 g/test. One hors (T) in the treatment group ate locoweed each time it was offered in the pen, but ate no locoweed while grazing. In the grazing trial, control horses averaged 8.6% of bites of locoweed (P<0.01) during the grazing portion of the study, whereas treated horses averaged <0.5%. One treated horse (S) accounted for all consumption; he consumed 15% of his bites as locoweed in a grazing bout on d 2 of the field study. Thereafter, he was dosed a second time with LiCl and ate no locoweed in the subsequent five days. Three of six horses required two pairings of LiCl with fresh locoweed to condition a complete aversion. The results of this study indicate that horses can be averted from locoweed using LiCl as an aversive agent, and this may provide a management tool to reduce the risk of