Dryness leads to poisonous grazing
With dry weather in many parts of the area, the potential for animals to eat toxic plants increases, mostly because they’re hungry and not much forage is available for grazing.
Most poisonous plants taste terrible, but livestock may accidentally eat some toxic plants while foraging, too. Knowing which weeds (and parts) are toxic and which ones are not is valuable information for this season.
Poisoning effects can appear a few ways and affect certain animal systems (sometimes more than one).
For example: sudden death (poison hemlock and nitrate accumulators); cardiovascular (dogbane and foxglove); digestive (pokeweed and most of the nightshade family); blood (red maple and bracken fern); and nervous (buckeye and horse chestnut).
Area offenders. Some of the more common and notable weeds in the area include bracken fern, pokeweed, cressleaf groundsel, water hemlock and poison hemlock.
Bracken fern toxicity in horses stems from vitamin B1 deficiency. Horses will usually not eat bracken fern if there is anything else to eat. The symptoms include weight loss, muscle tremors and death. It usually becomes a problem in drought conditions when more favorable species do not grow as well.
Pokeweed is common in Ohio and toxic to most livestock. This is one plant that animals will eat even when there is sufficient grazing available. The roots are the most toxic part of the plant and the berries are the least toxic.
Symptoms of pokeweed toxicity include cramping, vomiting and diarrhea.
Cressleaf groundsel contains an alkaloid that causes liver damage in animals. The flowers are the most toxic part of the plant.
Liver damage may not be immediately apparent. By the time symptoms appear, damage has already been done. The symptoms include lack of coordination, anorexia, depression, diarrhea and eventually death.
Hemlock. Both water hemlock and poison hemlock are toxic to livestock. Water hemlock is extremely dangerous and is one of the most toxic plants in North America.
Animals can show signs of toxicity within 15 minutes of ingestion and can be dead within two hours of the first symptoms. This plant causes convulsions, which lead to asphyxia and cardiovascular collapse.
Poison hemlock is less toxic but can cause death if the animal eats enough of it. Symptoms include lack of coordination, shaking and muscle weakness. It is more commonly a cause of abortions and birth defects.
The weeds we discussed here are certainly not an exhaustive list. For more information, see these Web sites for reference: The Ohio State University Extension factsheet on plants poisonous to horses: http://ohioline.osu.edu/b762/b762_24.html.
Penn State has a nice resource as well, found at http://vetextension.psu.edu/Resources/. From this site, click the search box in the upper-right corner and type in “poisonous plants” for a document on various types of poisoning and plants.
Illustrations. A book with full-color pictures that may be helpful to grazers is A Guide to Plant Poisoning of Animals in North America, by Anthony P. Knight and Richard G. Walter (2001, Teton NewMedia, WY).
If you have suspicious weeds in your pasture or hayfield and have questions regarding the possible toxicity, give your county Extension office a call for assistance.
(The authors are Ohio State University Extension agriculture and natural resources educators in Wayne County, Ohio.)