After a winter of dry hay, last years grass from the horse's point of view, anything green can be very tempting for a horse. During certain seasons or under certain pastures conditions some plants can be more dangerous to horses than at other time. A time of high risk can be the early spring. Many toxic weeds sprout out before the grasses do. During a dry period without rain, late fall as the grass is dying off, even an overgrazed pasture can cause your past conditions to be at high risk for poisonous plants.
Allowed these conditions in a pasture can give weeds a chance to grow and flourish. Horses may eat them under such conditions when normally they would leave them alone. Ryegrass that is intended for lawns may carry fungi (endophytes) that grow inside the plants. Tall fescue can be harmful to pregnant mares in their last trimester of pregnancy because it can harbor an endophyte. Toxins found in the leaves from the red maple tree that are normally at low levels after wilting became very strong making them a danger to horses. In the spring oak buds and young leaves can be toxic for horses. We often think our horses know instinctively to stay away from poisonous plants. NOT TRUE . If there is not plenty of good forage available, if a horse is bored, hungry, or thirsty they may be tempted to nibble on a poisonous plant.
Many poisonous plants taste bad to horses and they will avoid them, but not all do. It can be difficult to diagnose plant poisoning in your horse. The signs can mimic many other problems and they can vary. Symptoms may appear in hours of contact with the plant, or days, or even weeks after contact with the offending plant. If the poisoning is preliminary the signs may be subtle such as weight loss or assimilation to exercise. Some symptoms that can be indications of plant poisoning in horses are: gastrointestinal upset (diarrhea or colic), drooling or slobbering, unable to swallow, red skin, blistered skin, cracked skin, neurological signs (hyperexcitablility, depression or incoordination), weakness, rapid pulse and labored breathing.
To prevent your horse from being poisoned by a toxic pasture make sure you keep toxic plants from their food supply. Become familiar with the poisonous plants in the area where your horse is kept. The list of poisonous or potentially harmful plants can vary from one region to another. Check with your counties Cooperative Extension service. They can also offer suggestions for methods of elimination of poisonous plants that will be safe for horses. Universities can be another source to check for information about plants in a specific area.
After becoming familiar with poisonous plants in your area it is up to you to walk your pasture. Look for signs of these plants, especially at high-risk times (spring, fall, or branches after storms). Remember your horse can reach forage a good three or four feet beyond your fence line. Check anywhere you allow your horse to graze. Check the quality of your pasture. Is it thick and healthy or grazed down? Bare ground allows for toxic plants to take over. Eliminate any toxic plants you find. Inspect brushy areas and hedgerows along the pasture.
Toxic trees and plants may thrive in such areas. If you find any get rid of them. Do not overlook your hay supply. Drying will not eliminate toxins in plants that may be baled up in your horses hay. If the hay has broad-leaved weeds, reject it. If your hay is purchased locally, you will probably more readily recognize any toxic plants that might be in the bales. It is up to you to keep your horse's past and their other food supply free from toxic plants. Following these steps can prevent your horse from grazing in a toxic pasture and insure a high quality food supply.