Page 107 - July 2019

Some types of poisoning are irreversible and fatal, while others can be resolved with prompt emergency treatment.
bination of stress and the apples in his digestive tract leads to an acute case of colic.
Wild cherry (chokecherry) grows wild in most areas of the United States. It has dark green leaves and clusters of white or cream-colored blossoms that produce dark red or black fruit. The leaves contain a substance that produces cyanide and hydrocyanic acid poisoning when damaged. The chokecherry is most deadly when the leaves are damaged. Because the poison interferes with oxygen transfer to the cells, the affected horse suf- fers from acute oxygen starvation. The horse will breathe heavily, grow excited and agitated, then become weak and may suffer from convulsions before going into a coma. Symptoms appear soon after the leaves are consumed and, unless treat- ment is immediate, the horse may die. Cherry, plum, peach and apricot leaves are also toxic if wilted or otherwise damaged, so horses should be kept out of orchards. Cherry laurel, often planted in yards and gardens, is another potent source of hydrocyanic acid, as is crab apple. The chokecher- ry is often found in pastures, lining fence rows, or growing along streams in arid regions. It may be merely a tall shrub in dry places, but grows into a tree where there is plenty of water.
Rayless goldenrod, a bushy, unbranched perennial shrub, is also called “rosea” or “jimmy weed.” Most common in the Southwest, it grows two to four feet tall with yellow flowers. The toxic substance tremetol causes muscle tremors, depression, stiff gait, and weakness. Foals can be poisoned by nursing mares who eat the shrub.
Black locust is a legume with short thorns, creamy white blossoms and thin brown seed pods. It grows east of the Mississippi, and is used as an ornamental tree in other regions. The leaves, twigs, and bark are poisonous to horses, causing colic, diarrhea, dilated pupils, weak and irregular heartbeat, depression and death.
Red maple, also called “swamp maple,” is native to the eastern half of the United States. It can be quite poisonous to horses, killing them within a day or two after they’ve eaten small amounts of wilting leaves in the fall or nibbled them off fallen or trimmed branches. The wilted leaves contain a toxin that causes breakdown of red blood cells. Symptoms of red maple poison- ing include rapid breathing, weakness, depres- sion, brown urine and very dark blood.
Oleander is a common ornamental shrub in warmer regions that is deadly if eaten. One-fourth pound or less will kill a horse. Often just a few leaves can be deadly. Horses rarely eat leaves from the shrub itself, but if wilted or dried, they are more palatable because they don’t retain their bitter taste
but they do retain their toxicity. Oleander contains two toxins, oleandrin and nerioside, that affect
the heart much like digitalis, producing erratic heartbeat and diarrhea. Death may occur within a few minutes or hours. It’s best to assume that any ornamental tree or shrub is unsafe for horses to nibble on. Magnolia, azalea, privet, boxwood and rhododendron also cause illness in horses.
Black walnut trees are often grown in the eastern part of the United States and in Cali- fornia. Wood shavings from these trees cause colic and laminitis in horses bedded on them. In addition, horses at pasture can be seriously affected if they have access to black walnut trees. Pollen in spring causes allergic respiratory reac- tions, and chewing of bark or branches leads to laminitis and colic at any time of year.
Yew is a small ornamental evergreen tree or shrub with red berries. Its leaves are stiff and needlelike, dark glossy green on top and yellow-green under- neath. There are several species, including English yew, Japanese yew, and American or Canadian yew. Yew contains taxine, a highly poisonous alkaloid, even when dried, and has a depressing effect on the heart. About 4 ounces, or one mouthful, of yew needles can kill a horse. The animal dies of heart failure, often within minutes of nibbling on Yew.
Yew is poisonous to people and livestock. Symptoms include shortness of breath, muscle tremor and sudden collapse. With horses, death may be so sudden that some of the plant will still be in the mouth. Avoid these shrubs in landscaping and check your farm and neighbor- ing fence lines to make sure there’s not a poten- tially lethal hazard waiting around the corner for an unsuspecting horse.
Other trees that are mildly toxic if chewed by horses are oak (including the acorns), Ohio buckeye, and the Kentucky coffee tree. Horses consuming a lot of oak leaves or acorns may be severely poisoned.
Check all the plants in a pasture or paddock before putting horses in. Check all trees and shrubs — even if they are outside the fence line but within reach of the horses, or where branches or leaves can blow into the pens.
To avoid poisoning your horses, never dump trim- mings, pruned branches, or discarded garden plants near horse pens or pastures. Bored or curious horses may nibble on strange plants, even reaching under or through a fence to taste and eat them. Never let horses near ornamental shrubbery, plants or flowers. Remove fallen tree limbs or leaves from pens and pastures im- mediately after a storm. Carefully inspect bedding straw to make sure there are no weeds. When feeding hay, always take time to look, smell and inspect it for strange plants and discard anything you aren’t sure about.
Russian knapweed, if eaten over several weeks, causes irreversible brain damage. Signs include rigid jaw muscles and drowsiness. Horses starve from the inability to eat and are typically euthanized to spare them a slow death.
Equisetum, aka horsetail, scouring rush, or jointfir, may end up in meadow hay. Poisoning
is cumulative and signs include excitement and staggering. The poisonous enzyme destroys vitamin B1, as in Brackenern, and the horse must be treated with thiamine injections to be saved.
Black locust leaves, twigs, and bark are poisonous to horses, causing colic, diarrhea, dilated pupils, weak and irregular heartbeat, depression and death.
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EQUINE HEALTH