Poisonous Plants and Plant Toxins That Are Likely to Contaminate Hay and Other Prepared Feeds in the Western United States

Abstract

Livestock poisoning by toxic plants is a relatively common problem in pastures and rangelands and it is estimated to annually cost the livestock industry more than $200 million. However, these estimates are for grazing animals and the total cost is probably much greater because many animals are poisoned by contaminated feeds. Many poisonous plants are accessible to grazing livestock, but they are generally avoided and are not eaten, or they are eaten at doses that they do not produce detectable disease. In such cases toxic plants may not be more than a problem of displacing desirable nutritious plants. However, this is not always the case, especially when toxic plants contaminate prepared feeds. Poisonous plants incorporated in preserved forages, such as hay and silage, are much more likely to be eaten. This may occur because of increased competition from herd mates or by increased feeding pressure as prepared feeds are most often used in winter when alternative food sources are exhausted. Alternatively, the plants may become more palatable as they are diluted with palatable feed or the previously distasteful plant components are altered during forage preparation or storage. In addition, normally safe forages, under certain conditions, can produce and accumulate toxins. Identifying these toxic contaminates and understanding when forages may be toxic is critical in reducing poisoning and ensuring quality animal products. Our objectives of this review are to present basic principles of identifying contaminated feeds and sampling forages, introduce several common forages that under certain conditions can be toxic, present a brief description of plants that we have found contaminating feed in the western United States, and review how to treat or avoid such poisonings.