Page 104 - July 2019

• Equisetum is also called horsetail, scouring rush, or jointfir. Several species grow in meadows and floodplains or wherever the water table is high. These plants may end up in meadow hay. Poisoning is cumulative and may occur after horses eat hay contain- ing large amounts of horsetail or graze it in the pasture. Symptoms include excitement, muscle weakness, trembling, stagger-
ing, diarrhea and loss of condition. As in brackenfern, the poisonous element is the enzyme that destroys vitamin B1. If diagno- sis is made early, treatment with injections of thiamine can save the horse.
• Fiddleneck, fireweed, tar weed, buckthorn, and yellow burr weed are common weeds in wheat and grain crops in the West and Midwest, causing liver failure if eaten. Fid- dleneck may grow in pastures or hay fields. A single, large dose, or small amounts eaten over days or weeks can cause poisoning from pyrrolizidine alkaloids. These weeds aren’t very palatable, but a horse may
be poisoned by eating small amounts at pasture or in hay or grain over an extended period of time.
• Lantana is an ornamental flower com- monly found in yards and along roadways, especially in the Southeast, West and Southwest. Horses will consume the plant if other forage is poor or unavailable. Symptoms of poisoning are respiratory distress, diarrhea and low blood sugar, with the horse becoming dull and weak. Gener- ally, 20 to 30 pounds is fatal.
• Locoweed, aka crazyweed, milkvetch or poison vetch, is native to arid and semiarid rangelands; there are more than 50 variet- ies. This plant is a legume and part of the pea family with alternate leaves and pea- like blossoms. The seeds resemble garden peas in a dry, leathery pod. Most locoweeds and vetches grow in selenium-rich soils and concentrate selenium in their tissues. Some types are unpalatable and horses will eat them only when they are short on better feed, as in dry years or during a late spring when pasture grass is slow starting. Loco- weed comes up early, ahead of the grass. Other types of locoweed are quite palatable and vary in toxicity, ranging from good high-protein forage plants to extremely poisonous. Some are even addictive. Once a horse starts eating these, he seeks them out, even if better feed is available. In moder- ately toxic plants, the poison is cumulative and builds up to dangerous levels over a few days or weeks. The most toxic plants cause death within a few hours. The plant destroys nerve cells in the brain and even if a horse stops eating the plants, he can never completely recover.
“Most poisonous plants, trees, shrubs, and grasses vary in level of toxicity.”
102 SPEEDHORSE, July 2019
Lantana is found in yards and along roadways, and horses will eat it if other forage is poor. Symptoms of poisoning include respiratory distress, diarrhea and low blood sugar. 20 to 30 pounds is fatal.
With over 50 varieties, Locoweed concentrates selenium in their tissues. Types can be addictive and vary in toxicity, destroying nerve cells in the brain. Poison is cumulative in moderately toxic plants, building over days and weeks, while the most toxic can cause death within a few hours.
The toxic substance tremetol found in Rayless goldenrod causes muscle tremors, depression, stiff gait, and weakness. Foals can be poisoned by nursing mares who eat the shrub.
Fiddleneck, fireweed, tar weed, buckthorn and yellow burr weed are common in wheat and grain crops and cause liver failure if eaten. A large dose or small amounts eaten over time causes poisoning from pyrrolizidine alkaloids.
Water hemlock and poison hemlock cause incoordination, drooling and slow heart rate. Death is usually from respiratory failure. Treatment generally does not help and survival depends upon how much the horse has eaten. It takes less than a pound to kill a horse.
Senecio species contain pyrrolizidine
alkaloids that destroy the liver. The plants grow in early spring and are often found in first- cutting hay.
EQUINE HEALTH