THE CLINICAL AND MORPHOLOGICAL CHANGES OF INTERMITTENT LOCOWEED (OXYTROPIS SERICEA) POISONING IN SHEEP

Authors: Stegelmeier, Bryan; James, Lynn; Panter, Kip; Molyneux, Russell; Gardner, Dale; Lee, Stephen; Ralphs, Michael; Pfister, James

Submitted to: Poisonous Plants Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/20/2003
Publication Date: 11/1/2003
Citation: Stegelmeier, B.L., James, L.F., Panter, K.E., Molyneux, R.J., Gardner, D.R., Lee, S.T., Ralphs, M.H., Pfister, J.A. 2003. The clinical and morphological changes of intermittent locoweed (oxytropis sericea) poisoning in sheep. Poisonous Plants Symposium Proceedings.

Interpretive Summary: Locoweed poisoning affects livestock and wildlife throughout the world and the risk of locoweed poisoning can inhibit the productive use of natural resources. Poisoned animals often develop permanent neurologic disease making poisoned animals dangerous to use or to be around. Intermittent or cyclic grazing of locoweed infested ranges may avoid the permanent effects of locoweed poisoning. The purpose of this study was to determine the effects of intermittent dosing on the development of clinical and histologic lesions. Ten groups of 4 wethers were treated with Oxytropis sericea at doses of 1 mg swainsonine/kg bw/day for 45 days with varying dosing intervals and recovery periods. Sheep treated for 45 uninterrupted days were depressed, anorexic and reluctant to move. The serum biochemical changes were similar to those found in previous studies of locoweed poisoned animals. Microscopic changes included degeneration and vacuolation of many tissues that were most severe in neurons in the cerebellum and lower parts of the brain. Less severe clinical biochemical and microscopic changes were seen in animals with dosing periods of 9 and 15 days and recovery periods of 7 and 14 days. Though animals dosed for periods of 5 or fewer days followed by 7 and 14 day recovery periods had no clinical or microscopic changes. This suggests that animals may ingest locoweeds for short periods, 5 days or less, without developing behavioral or functional lesions if allowed withdrawal periods of 7 to 14 days. This supports the hypothesis that intermittent use of locoweed-infested ranges and pastures may allow use of valuable forages without permanently damaging animals.

Technical Abstract: Locoweed poisoning affects livestock and wildlife in many parts of the world and often inhibits the productive use of natural resources. Intermittent or cyclic grazing of these ranges may avoid the permanent effects of locoweed poisoning. The purpose of this study was to determine the effects of intermittent dosing on the development of clinical and histologic lesions. Ten groups of 4 wethers were treated with Oxytropis sericea at doses of 1 mg swainsonine/kg bw/day for 45 days with varying dosing intervals and recovery periods. Sheep treated for 45 uninterrupted days were depressed, anorexic and reluctant to move. They had increased serum alkaline phosphatase activity (ALP), aspartate aminotransferase activity (AST) and swainsonine concentrations with decreased a-mannosidase activity. Histologic lesions included subtle vacuolation of many visceral tissues with extensive vacuolation and occasional pyknosis of cerebellar Purkinje cells and large neurons of the basal ganglia and medulla. Less severe clinical, biochemical and histologic changes were seen in animals with dosing periods of 9 and 15 days and recovery periods of 7 and 14 days. Though animals dosed for periods of 5 or fewer days followed by 7 and 14- day recovery periods had mildly increased serum AST activities, no clinical or histologic lesions were detected. This suggests that animals may ingest locoweeds for short periods, 5 days or less, without developing behavioral or functional lesions if allowed withdrawal periods of 7 to 14-days. This supports the hypothesis that intermittent use of locoweed-infested ranges and pastures may allow use of valuable forages without permanently damaging animals.