Poisonous Plants and Effects on Animals

Livestock animals are at the mercy of toxic plants when these plants are present in feeds or hay. Alfalfa hay or forage, which is commonly offered to livestock animals, may pose a risk if contaminated with poisonous plants. Undesirable effects may result from ingestion of large amounts of alfalfa by livestock but may also be associated with the ingestion of small amounts of highly toxic plants present in alfalfa. In many cases, livestock animals, especially horses are selective about what they eat, but instances such as herbicide applications may change palatability or increase toxicity in some plants. Most plant poisonings have no specific treatments and thus, are best prevented by avoiding exposure to toxic plants in the first place. Hay and feed should be carefully inspected for contamination with potentially toxic weeds before the first feeding and owners should establish excellent working relationships with suppliers and growers. Producers and farm managers, along with veterinarians and diagnosticians play important roles, and all contribute information that may be important to a poisoning case. Once all the information is available, all evidence is collected, and proper sampling of specimens has occurred, a summary of findings can be provided and will be instrumental in preventing reoccurrences. Livestock poisoning associated with the ingestion of hay contaminated with nitrate accumulators, pyrrolizidine alkaloids, summer pheasant’s eye, foxtail, and oleander are discussed. Awareness of poisonous plants growing in a certain geographical region and their associated clinical signs are instrumental in making a diagnosis, and initiate treatment. More importantly, the recognition of poisonous plants in hay or forage may help prevent plant poisonings in animals. In addition, botulism is briefly discussed.