Types of toxins in plants Alkaloid – any number of bitter organic substances, such as caffeine, morphine, quinine and strychnine, having alkaline properties and containing nitrogen. Found in plants and often used as drugs and stimulants, but can have a toxic effect on the human or animal system. Prussic Acid - (hydrocyanic acid) a deadly poison which is produced under certain conditions: frost, drought, trampling, bruising, wilting. Ecological conditions are factors in the formation of prussic acid. Plants grown in poor soil have less acid than when grown in nitrate rich soil. These plants seem to lose their poison when thoroughly dry, as the acid is very volatile and passes into the air while the plant is drying. Prussic acid is a cyanide compound that can kill animals within minutes of ingestion under the right circumstances. Cyanide interferes with the oxygen-carrying function in the blood, causing animals to die of asphyxiation. Symptoms include difficult breathing, excess salivation, staggering, convulsions and collapse. Affected animals will have bright cherry red mucous membranes from the cyanide. Ruminants are more susceptible than horses or swine because they consume large amounts of forage quickly and the rumen bacteria contribute to the release of the cyanide from consumed plant tissue.

Most Common Poisonous Plants in MD and PA In Order From Most to Least Toxic Hemlock/water hemlock All parts are toxic, a piece the size of a pea can kill a human. Water hemlock, trampled into water, has been known to kill livestock. Toxic year-round, most likely to be eaten in early spring. Symptoms: salivation, bloating, colic, dilation of pupils, rolling of eyes, labored respiration, diminished frequency of breathing, irregular heart action, loss of sensation, uncertain gait, falling, ending with complete paralysis, and death within a few hours.

Ornamental yew/Japanese yew All parts contain toxic alkaloids, ¼ lb of clippings will kill. People, often not knowing better, will place trimmings in animal enclosures. Yew is often planted as an ornamental plant around houses. Having the shrubs too close to fencelines is a common way that animals come in contact with them. Symptoms: colic, diarrhea, tremors, dilated pupils, respiratory difficulty, weakness, fatigue, collapse, coma, convulsions, circulatory failure, and death. Death is sometimes so rapid that few well-developed symptoms appear. Survival is rare.

Mountain Laurel, Rhododendron, and Azalea All parts toxic, 2 or 3 leaves may produce severe toxicosis. Because they retain their green leaves year-round, most toxicoses occur in the winter and early spring, when other forage is unavailable. Grows in shady areas, and often planted as an ornamental. Symptoms: disinclination to eat, repeated swallowing, profuse salivation, grating of the teeth, frothing at the mouth, loss of energy, slow pulse, low blood pressure, incoordination, dullness, depression, stupor and death.

Nightshade (black, bittersweet, deadly, silverleaf), horse nettle, Jerusalem cherry, ground cherry Generally, the leaves and green fruits are toxic. Eating the juice from wilted leaves may be especially toxic. Poisoning by these species occurs primarily when animals are confined in overgrazed fields where the plants are abundant. The hazard of poisoning varies, depending on the plant species, maturity of plants, and other conditions. One to ten pounds can be fatal. Symptoms: Colic, convulsions, dilated pupils, weakness, depression, death from paralysis of the lungs.

Wild cherry, chokecherry, Sudan grass, sorghum When plants are damaged due to frost, drought, bruising, trampling, wilting, they produce prussic acid. This is found mostly in the leaves, bark, and shoots. Most common exposure to wild cherry and chokecherry is when limbs are blown down or are trimmed and thrown into animals’ enclosures. They are common trees in many areas, and are often found in woods edges. They kill by inhibiting the red cells’ ability to transport oxygen. When dried, there is no longer any danger. Symptoms: anxiety, staggering, falling down, convulsions, rolling of eyes, tongue hanging out, colic, difficulty breathing, and death by suffocation.

Red maple Wilted red leaves contain toxin, can remain toxic for 30 days after falling. Early spring and fall are times to watch for it. A common tree, mostly in damp areas. Symptoms: similar to oak poisoning.

Oak Toxin is ingested by eating young shoots, leaves, and acorns if eaten in quantitiy. A common tree in most areas. Symptoms: anorexia, constipation becoming diarrhea, colic, thirst, and excessive urination.

Black locust Toxin is ingested by eating inner bark, roots, wilted leaves, and seed pods. A common tree in many areas. Symptoms: stupor, depressed heart action, weak pulse.

Black walnut Pollen in spring can cause allergic respiratory reactions and laminitis. Laminitis and colic occur from eating bark or fallen walnuts. Standing in walnut shavings as bedding causes laminitis, too. A common tree in many areas. Bracken fern All parts are toxic, usually eaten in the fall when pasture is poor, or in hay. Drying does nor reduce toxicity. Inhibits uptake of vitamin B1. Must eat it frequently for a period of 30 – 60 days for toxicity to build up. Symptoms: loss of appetite, and loss of coordination.

Horsetail Usually eaten in hay, must be eaten for 2 – 5 weeks for symptoms to appear, The alkaloid equesetin causes thiamin deficiency. Symptoms: unthriftiness, diarrhea, loss of weight, loss of muscular control, followed by swaying and staggering. Animal falls and cannot rise. Violent struggle weakens the animal and death is caused by exhaustion.

Jimsonweed Whole plant is toxic, seeds are particularly poisonous. Horses usually avoid the plant due to its noxious odor and taste. Poisoning most often occurs from the leaves of young plants getting into hay, or pasture with nothing else to eat. Symptoms: rapid pulse, rapid breathing dilated pupils, restlessness, nervousness, muscular twitching, drinking a lot, diarrhea, loss of appetite, weight loss, in fatal cases, the pulse remains rapid but weak, breathing becomes slow and irregular, body temperature becomes subnormal, and convulsions or coma precede death.

Spreading dogbane/Indian hemp Whole plant is toxic, eaten only when pasture is poor, early spring or late fall. Symptoms: increased temperature and pulse, warm body, cold extremities, sweating, dilation of pupils, discoloration of mouth and nostrils, sore mouth. The animal refuses to drink for 24 hours preceding death.

Cocklebur Seeds and seedlings contain the toxin. It is not lost upon drying. Most hazardous at seedling stage because of its toxicity as well as palatability. Mature plants are seldom eaten due to bitterness and rough texture. Symptoms: signs develop within 2 – 24 hours, loss of appetite, rapid weak pulse, difficulty breathing, muscular weakness, prostration, and spasmodic contraction of leg and neck muscles. Potentially lethal hypoglycemia may occur.

Pokeweed Whole plant is toxic, although root is most toxic. Animals may feed on poke plants in the spring when the plants are succulent or if the grass is very short, they may browse on the tips of the plants. Unless there is almost nothing else to eat, the animals will not eat the tops or the berries later in the summer. Pokeweed is harmless when it is dried. Symptoms: horses rarely eat enough to cause more than a colic.

May Apple Entire plant toxic, except “apple” when ripe. Not normally eaten but some animals develop a taste for it. Must eat continuous large amounts to show symptoms. Grows in moist, shady, wooded lowlands. Symptoms: colic, bloody feces, convulsions, and death.

Buttercup Fresh leaves and tops contain toxin. This toxin is an acrid volatile substance that leaves the plants as they dry, so buttercups in hay are harmless. They have a very bitter taste and are usually only eaten by accident, when they are pulled up from soft, damp earth along with other plants. They must be eaten in quantity to be toxic. Symptoms: salivation, loss of appetite, colic, diarrhea, and slow pulse.

Bouncing Bet Toxin irritates mucous membranes of digestive tract and cause colic. Common horse chestnut Nut is toxic.

Wild Onion Entire plant contains toxins. Toxin causes rupture of the red blood cells. Horses are only slightly susceptible to the toxin. Most common time for poisoning occurs in cool spring weather when grass growth is delayed and wild onions are available in comparatively large quantities for grazing. Symptoms: urine discoloration from red wine to almost black. Muscle weakness, rapid breathing, and rapid heart rate may be noted if hemolysis is sufficiently severe.

1.What is more toxic, yew, or buttercup? Yew 2.How do horses often come in contact with yew? Yard trimmings thrown over a fence, and yew planted near fences and barns. 3.Why will horses sometimes eat bitter, foul-tasting toxic plants? When there is little else to eat in a field, especially in spring, when plants are young and tender. 4.In what condition do cherry leaves have to be in order to be toxic? They have to be wilted or damaged 5.What’s a common way that horses are exposed to toxic cherry leaves? When a tree or branches fall in a pasture. 6.What trees have toxic seeds or nuts? Oak, black locust, black walnut, horse chestnut. 7.What toxic plant is most commonly eaten in hay? Horsetail jimsonweed, and bracken fern 8.What toxic plants are harmless when dried? Pokeweed, buttercup 9.What plants are needed to be eaten in large quantities in order to be toxic? May apple, buttercup 10.Have you noticed any of these plants in pastures in this area? Should you be concerned? Why, or why not? Common ones are: wild cherry, red maple, oak, black locust, black walnut, cocklebur, pokeweed, buttercup, wild onion.

Most are not concerning, because horses won’t eat them because of bitter taste or low palatability. Others need to be eaten in very large quantities. Keeping pastures healthy, and feeding supplemental hay in fields can reduce the risk. Removing fallen nuts, and fallen cherry branches can help.