Toxicity of Nitro-Containing Astragalus to Sheep and Chicks

Abstract

Several species of Astragalus that contain organic nitro compounds were tested for toxicity to sheep and 1-week-old chicks. Methemoglobin analyses in sheep indicated that nitro compounds in A. diversifolius, A. convallarius, and A. pterocarpus resembled 3-nitro-1-propanol in toxicity and rate of absorption from the digestive tract. Nitro compounds in A. cibarius and A. canadensis were more closely related to 3-nitropropanoic acid in toxicity and rate of absorption. A. pterocarpus, A. convallarius, and A. diversifolius have been categorized as "Class I" species because they produce acute oral toxicity in sheep at less than 100 mg NO2/kg of body weight. "Class II" Astragalus (A. canadensis and A. cibarius) produce acute toxicity in sheep only if oral dosage exceeds 100 mg NO2/kg. Class I species are more likely to cause livestock losses on the range.