More than 100 species of toxic plants infest Texas rangelands. The impact of these plants on the ranch business is not restricted to direct loss in terms of livestock death. Depressed conception rates, lower weaning weights, increased supplemental feeding costs and reduced production of more desirable range forage are examples of indirect losses associated with toxic plants. Total direct and indirect losses attributed to perennial broomweed, is estimated to exceed $30 million per year in Texas (McGinty and Welch, 1987).

Some toxic plants produce easily identifiable symptoms. For example, sacahuista causes photosensitization (hyper-reaction to sunlight), which results in obvious inflammation, swelling and sloughing of the skin. But accurate diagnosis of poisonous plant problems can be difficult. Chronic poisoning from perennial broomweed usually causes abortion, which may be mistakenly blamed on improper management practices or disease. Many cases of livestock poisoning are misdiagnosed and millions of dollars wasted with improper treatment.

The time frame over which symptoms occur adds to the difficulty of diagnosis. Plants which produce toxic amounts of prussic acid (i.e., sorghum species) can kill animals within 15 minutes. On the other hand, threadleaf groundsel may not produce clinical signs or death for 9 to 12 months after consumption.

When a sick or dead animal is found, the first step in diagnosis is to determine whether the cause is plant poisoning or infectious disease. To do so it is necessary to carefully observe symptoms exhibited by affected animals and to have a thorough knowledge of plants native to the area.

Assuming a poisonous plant is responsible, the next step is to identify the plant. Again, symptoms are important when narrowing the suspected plant to one or a few species. It is also helpful to observe if any toxic plant species within the pasture exhibit evidence of grazing use. Finally, the rumen of a dead animal can be opened and a sample obtained of the ingested forage. Careful examination of the rumen contents can assist in identification of the toxic plant responsible. [Next Page]