Toxicological investigations on Toano, Wasatch, and stinking milkvetches

Abstract

Toano milkvetch (Astragalus toanus Jones) synthesizes the beta-D-glucoside of 3-nitro-1-propanol (miserotoxin), a highly toxic aliphatic nitro compound, and also accumulates toxic levels of selenium. The toxicity of Toano milkvetch to 1-week-old chicks was compared with Wasatch milkvetch [Astragalus miser var. oblongifolius (Rydb.) Cronq.], which contains only miserotoxin but does not accumulate selenium; stinking milkvetch (Astragalus praelongus Sheld.), which accumulates selenium but does not contain miserotoxin; and a combination of Wasatch milkvetch and stinking milkvetch. The LD50 for chicks fed Toano milkvetch was 67.8 mg NO2/kg plus 2.7 mg Se/kg of body weight. The LD50 for Wasatch milkvetch was 105 mg NO2/kg and for stinking milkvetch 5.9 mg Se/kg. The LD50s of a combination of Wasatch milkvetch and stinking milkvetch were 66.1 mg NO2/kg and 2.7 mg Se/kg. When miserotoxin and selenium were fed together, either in Toano milkvetch or the Wasatch-stinking milkvetch combination, the LD50 for each compound was significantly lower than when they were fed separately. If seleniferous and nitro-bearing species grow sympatrically, livestock might be poisoned at lower concentrations of the individual toxic compounds if they grazed both species.