“An Unaddressed Issue of Agricultural Terrorism: A Case Study on Feed Security”, 2004-11-01 (; backlinks; similar):
In the late winter of 2003, a number of livestock animals in the Midwest were poisoned due the accidental contamination of a popular commercial feed with a lethal additive.
Although all the evidence indicates this incident had no malicious or terrorist intent, it is informative as a case study highlighting potential security implications with respect to a terrorist event directed at US agriculture.