CM-CN-MR-2-PoisonousPlantsby George Looby, DVM
Now the snow is gone, and most of us are waiting impatiently for spring to arrive. The first harbingers of the season have blossomed, but for every group of early bloomers there are a few plants that pose potential threats to livestock and pets. After a winter on dry forage and silage, the natural inclination of animals turned out to pasture is to seek out greenery. Unfortunately, all that is green is not healthy, nutritious or beneficial.
The mountain laurel is often found in wooded areas with rocky outcroppings and ledges. This habitat is often used as pasture for athletic animals, such as goats, where it may be eagerly eaten.

Ingestion of even rather small amounts of the leaves may produce symptoms of gastric irritation and if quantities are large enough may prove to be fatal. Treatment is symptomatic and often, activated charcoal can be life-saving, if administered early.
Horses seem to enjoy ingesting the wilted leaves of the red maple, especially when pasture grasses have been overgrazed. It is critical that the horse owner recognizes these trees and removes them from any lot where horses are turned out. If tree removal is not an option, the owner should remove the horse from this pasture. When this foliage is damaged, the leaves to elaborate a toxin which destroys red blood cells, rendering the animal extremely anemic. Signs may include discolored urine, jaundice and weakness. Prompt treatment is necessary, and activated charcoal given by tubing may act to deactivate the toxins. Blood transfusions, if available, are high on the list of recommended treatments.
Livestock owners should have a good working knowledge of the plants found on their property to help avoid unnecessary emergencies. One of the classics toxic plants is the black cherry. When its leaves are damaged by frosts, storms, or when eaten by cattle, they can turn lethal. The best course of action is not to allow cattle graze in pasture where these trees are found or entirely remove them.
Cockleburs — which are often confused with burdocks — share the characteristic of bearing toxic fruit. Very young, emerging cockleburs are especially toxic to young pigs. Before turning this group into new pasture, a walk around to ensure these plants are absent. Administering oils orally to animals after ingesting the fruit may be helpful. Additionally be sure to keep the affected animals warm and dry.
Many ornamentals possess toxins lethal to animals. One such common plant is the yew. Take care that livestock does not have access to trimmings from these plants. Eating just a small amount of plant material can be fatal often in a very short time.
The bracken fern, commonly found in poorer soil, contains a toxic material which, when eaten over time, will destroy thiamine, one of the more important members of the B vitamin complex. The development of symptoms tends to be rather slow and insidious. The acute form oftentimes shows in cattle as signs of an acute hemorrhagic condition, with blood showing from all body openings. Horses may show signs of a neurological condition through incoordination, crouching and legs positioned in a saw horse posture. Treatment consists of thiamine replacement over a period of time with monitoring of the animal’s platelet level a good aid in developing a prognosis.
In the spring, when there is the possibility of a late frost, care should be exercised in pasturing Sudan grass. Sudan grass that has been frosted will produce hydrocyanic acid, also known as prussic acid, which can have a devastating effect on cattle. If there is even a remote possibility that a frosted pasture has any amount of Sudan grass growing in it, avoid putting cattle in to graze. The standard treatment for the ingestion of this poision has been sodium nitrate followed by sodium thiosulfate, both given by IV. The proper amount depends on the weight of the animal. The treatment is best carried out by a veterinarian.
Although not a poisonous plant problem, grass tetany is somewhat related in that it can often be mistaken for such. Grass tetany may be seen in the spring, when cattle are on lush pasture consisting of cereal grains such as oats, rye or wheat. These most appetizing grasses are usually high in potassium and nitrogen, which can cause a reduction in the absorption of magnesium. Magnesium deficiency does not become apparent until the calcium level in the blood drops below a critical level. Animals so affected may show signs of hyperactivity before they collapse and convulse.

Treatment consists of IV solutions of calcium and magnesium, removal from affected pasture and magnesium supplementation.
Sweet clover toxicity is another result of inappropriate crop handling. Sweet clover naturally contains coumarines which, when subjected to the wrong conditions, are converted in to dicumarol, which is toxic. The most commonly seen cause of this conversion is excessive moisture, which promotes mold growth. Damaged round bales should always be fed with caution, especially the outermost part.

The appearance of symptoms may vary greatly depending on the amount eaten, the age of the animal and the dicumoral content of the haycrop being fed. Dicumarol is an anticoagulant which interferes with normal blood clotting, allowing for excessive bleeding from even the most insignificant wounds. When doing a post mortem on suspect animals it is possible to see large pools of unclotted blood under the skin and elsewhere. Treatment is blood transfusions and administration of vitamin K3.
Good management is the key to preventing poisoning in your pastures. Taking a few moments to do a personal survey might prove well worth it as we move further into the season.