Three cows fed Chenopodium album hay died 30 min after showing ataxia, bluish-brown mucous membranes, rapid and difficult breathing, increased heart rates, tremors and coma. Brown-colored and badly coagulated blood was the prominent necropsy finding. Slight pulmonary edema was prominent and all visceral organs were hyperemic. The hay contained 2,500 ppm nitrate-nitrogen and 11 ppm nitrite nitrogen.