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Submitted to: Veterinary Clinical Toxicology
Publication Type: Book / Chapter Publication Acceptance Date: 1/1/2003 Publication Date: 1/1/2004 Citation: Stegelmeier, B.L. 2004. Nitropropanol glycosides (astragalus, coronilla). Veterinary Clinical Toxicology. Interpretive Summary: The toxic nitro-compounds (3-nitropropanol, 3-nitropropionic acid and miserotoxin, the glucoside of 3-nitropropanol) have been identified in over 600 species of plants. These include many species of Astragalus that commonly poison livestock in North America. Though human poisoning is uncommon, NPA can contaminate feed or foods causing significant damage, as it is a potent neurotoxin. NPA inhibits cellular metabolism and poisoned animals develop labored breathing and muscular weakness. These animals have severe lung disease and abnormal gait (the rear feet interfere called 'cracker heels'). Poisoned horses may be reluctant to back up. Poisoned animals become weak and emaciated and generally die within several weeks. Current recommendations are that cattle can safely use grasslands containing milkvetch, if adequate forage is available. In wooded areas, it is more dangerous and other precautions should be taken. Grazing later, after the plants begin to senesce has also been recommended. Toxin metabolism may also be enhanced as rumen microbes become adapted to metabolizing nitrocompounds. Most of these toxic vetches may also be controlled with herbicides Technical Abstract: The toxic nitro-compounds (3-nitropropanol, 3-nitropropionic acid and miserotoxin, the -D-glucoside of 3-nitropropanol) have been identified in over 600 species of plants. These include many species of Astragalus that commonly poison livestock in North America. Though human poisoning is uncommon, NPA can contaminate feed or foods causing significant damage, as it is a potent neurotoxin. NPA inhibits succinate dehydrogenase, fumerase and aspartase, important enzymes of the Krebs or tricarboxylic acid cycle. Lesions appear to be due to inhibited cellular oxidative phosphoralation, decreased energy production and loss of cellular homeostasis. Poisoned animals develop dyspnea, rales, stridor, and muscular weakness. These animals have severe emphysema, abnormal gait (the rear feet interfere called 'cracker heels'), rear limb proprioceptive defects and goose- stepping. Poisoned horses may be reluctant to back up. Poisoned animals become weak and emaciated and generally die within several weeks. Current recommendations are that cattle can safely use grasslands containing milkvetch, if adequate forage is available. In wooded areas, it is more dangerous and other precautions should be taken. Grazing later, after the plants begin to senesce has also been recommended. Toxin metabolism may also be enhanced as rumen microbes become adapted to metabolizing nitrocompounds. Most of these toxic vetches may also be controlled with herbicides. |
