Toxic Weeds in Hay and the Effects on Livestock

Eliminating toxins from the hay begins in the field. However, toxic weeds frequently end up in hay and forage and pose a serious risk to livestock. The effects of poisonous plants on animals depend on the amount ingested and the individual weed present in hay. Many indications for poisoning exist. Obvious cases involve sudden onset of disease in a number of animals. Finding of common feed or environmental conditions will further support a suspicion of poisoning. A toxicosis is also suggested in the animal that is found "suddenly dead". Some toxic weeds may result in acute poisoning while others have to be ingested over a period of weeks to months before clinical signs of illness develop. Most plant poisonings have no specific treatments and thus, are best prevented by avoiding exposure to toxic plants in the first place. Awareness of poisonous plants growing in a certain geographical region and their associated clinical signs are instrumental in making a diagnosis, and initiating treatment. More importantly, the recognition of poisonous plants in hay or forage may help prevent plant poisonings in animals. It is often prudent to consult with a veterinary toxicologist at the earliest stage of a case, especially if one is available in your proximate area. Many potential poisons are unique to a geographic location, or a specific time of year. The veterinary toxicologist is uniquely qualified to discuss differential diagnoses, sampling techniques, and potential treatment options. Alfalfa hay has been contaminated with poisonous plants and has resulted in illness and death of animals. The presence of nitrate accumulators, pyrrolizidine alkaloid-containing plants, summer pheasant’s eye, foxtail, and oleander are discussed as these weeds are most commonly associated with alfalfa hay. In addition, spoiled forage or the presence of decomposed animal carcasses in hay can result in botulism and blister beetles have been found in alfalfa hay resulting in disease in cattle.