Page 103 - July 2019

COMMON OFFENDERS
Here is a list of some of the more common toxic plants found in various parts of the U.S.
• Brackenfern is a large perennial herb that
grows in burned-over areas, woods and shady places, but it also grows on dry, sandy, or gravelly soil. Horses will consume this plant when other feed is scarce, when it is mixed in hay, or when they are allowed to grab a snack along the trail. This fern contains an enzyme that inhibits absorp- tion of thiamine (vitamin B1) in the gut. Because the affected horse cannot absorb the B1, symptoms present as vitamin B1 deficiency, including deteriorated nerve function, loss of coordination, weight loss and depression. The horse will stand with back arched, legs apart and muscles twitch- ing. Symptoms develop slowly over days or weeks after eating a large amount of fern and if affected horses are not treated, they will eventually die, however, if the horse
is taken off the offending feed and treated with IV injections of thiamine hydrochlo- rate when symptoms first appear, he will most likely recover.
• Castor beans are grown as a crop for cas- tor oil in California and the Southwest and also as an ornamental plant in other regions. The seeds are the most toxic part of the plant causing mild colic, diarrhea, sweating, and a thundering heartbeat. Only a few ounces of castor beans can kill a horse.
• Cockleburisanannualplantthatgrowsin lakebeds, lowlands along rivers, and dis- turbed soils of fields, pastures, and roadways. Poisoning from this plant occurs mainly when horses eat the leaves in early spring because seedlings are more toxic than mature plants. Symptoms include: rapid and weak pulse, labored breathing and spasmodic contractions of the leg and neck muscles.
• Crotalaria,amemberofthepeafamily, contains pyrrolizidine alkaloids that destroy the liver. In the Midwest, the plant is called “rattleweed.” In Florida, it may be called “showy crotalaria.” The effects of liver damage may not show up right away because the liver is a large organ that continues to function until about 60% has been destroyed. Then, liver failure is quite sudden, with the horse dying within three to five days.
• Death camas grow on foothills and pastures in western and plains states. It takes less than 10 pounds of it to kill a horse, but the bulb (root) is the most deadly part of the plant. In moist soil, the root may pull up and be eaten. Symptoms of poisoning are excessive saliva- tion, weakness, difficulty breathing and coma. Death occurs soon, within a few hours to two days after ingestion.
“Certain plants absorb substances from the soil that accumulate to toxic levels.”
Wild delphinium, or larkspur, can kill a horse if he exerts himself after eating the plant due to impaired muscle activity and impaired breathing.
Death camas ingestion causes salivation, weakness, difficulty breathing and coma. Death occurs quickly, within a few hours to two days.
White snakeroot contains the alcohol tremetol, which damages the liver, and enzymes in the plant damage the heart muscle. It can be excreted in
a mare’s milk and poison a foal. Symptoms of poisoning include weakness, lethargy, stiffness and incoordination. A lethal dose is two to 10 pounds of plant material.
Signs of yellow star thistle poisoning include twitching lips, flicking tongue, involuntary chewing movements and drowsiness. Animals have trouble eating and drinking because the muscles of the jaw and lips become rigid, but they are able to swallow. Some horses will eat enough to cause permanent brain damage.
Brackenfern has an enzyme that inhibits absorption of thiamine in the gut and presents as vitamin B1 deficiency. It can cause deteriorated nerve function, loss of coordination, weight loss, depression and eventually death if not treated.
The nightshade family includes black nightshade, aka horse nettle, which contain the alkaloid solanine that causes nervous system impairment, digestive problems and abdominal pain. One to 10 pounds of black nightshade is fatal to a horse.
SPEEDHORSE, July 2019 101
EQUINE HEALTH