[Wikipedia] Toxicity in Large Amounts To Livestock: Like many other species of Amaranthus, this plant may be harmful and even deadly when fed to cattle and pigs in large amounts over several days. Such forage may cause fatal nephrotoxicity,[12] presumably because of its high oxalate content. Other symptoms, such as bloat or methylglobineamia in the most severe cases, might reflect its high nitrate content.[13] However, when supplied in moderation, it is regarded as an exceptionally nutritious fodder. (link added by Mary Ann Machi)