Aliphatic Nitro Compounds in Crownvetch: A Review¹

Aliphatic nitro compounds found in crownvetch ( Coronilla varia L.) can adversely affect animals. They are glucose esters of 3‐nitropropanoic acid (NPA) and are found primarily in the Coronilla , Astragalus , and Indigofera genera of Leguminosae family, as well as in other families. Methods have been established for isolation, identification, and analysis of these compounds. The toxicology of NPA in nonruminant animals has been studied, and symptoms produced by NPA, including methemoglobinemia, have been described. Recent data support the hypothesis that NPA exerts its toxic effect by irreversibly inhibiting the mitochondrial enzyme, succinate dehydrogenase. During this event, nitrite ion is released, which results in methemoglobinemia. In contrast to nonruminants, ruminants rarely exhibit toxic symptoms, because NPA is metabolized to nontoxic products by rumen microorganisms. Growth and storage conditions influence the levels of NPA in crownvetch. Information concerning the inheritance and function of NPA in crownveteh is inadequate. Crownvetch may be safely fed to ruminants but, if fed to nonrnminants, its concentration should not exceed 5% of the diet.