By Martin W. Adams, PhD, PAS – Equine Nutritionist for Southern States
How do you know what plants are safe, and what are some ways to prevent the potential for acute or chronic poisoning of your horses in their pasture? Generally, horses naturally avoid toxic plants, as they usually have an undesirable taste, but there can be exceptions. Overcrowding (less than 2 to 3 acres per horse) and overgrazed pasture (lack of fertilization, regular mowing or weed control) opens the door for the encroachment of toxic plants. Even if a sufficient diet of hay is fed, horses may graze toxic plants out of boredom.
Many poisonous plants that are a concern for horses are only slightly to moderately toxic and not life-threatening only if consumed in a fairly large quantity, at certain times of the year, or under conditions of heat and drought. Buttercup, Milkweed, Oak, Walnut, Pokeweed, Foxtail, Dogbane, Horsetail, Perilla Mint, Johnsongrass, Nightshade and Star of Bethlehem are examples. Although many of these plants are found in pastures, they’re usually not consumed in a sufficient amount and are diluted by intake of pasture grasses to not be a problem. However, some plants are highly toxic with a consumption of just a few pounds, examples being Wild Cherry, Red Maple, Horse Chestnut, Yew, Rhododendron, Lantana and Laurel. The last four plants listed are commonly used as ornamental plantings near a barn or paddock and could present an opportunity for a horse to consume enough for a fatal toxic dose. Horse eating leaves from low hanging and/or downed tree limbs that are wilted (wild cherry and red maple) are a common cause for equine deaths.
To minimize the possibility of horses grazing toxic plants:
Inspect your pasture to identify plants in and around your pasture that could be a problem.
Don’t allow overgrazing so there is enough desirable forage to dilute weeds that may be moderately toxic, like buttercups in the early spring, for example. Allow 30-day rest periods to allow grass to recharge their root reserves and grow to a minimum height of 4 inches for warm-season and 6 inches for cool-season grasses before allowing horses in to graze again. If not, the grass plants in your pasture can die out and be replaced by weeds and toxic plants.
Maintain proper soil pH and keep potassium, nitrogen and phosphorus fertility at proper levels with regular soil testing and fertilizer application to provide vigorous growth of pasture plants.
Control weeds and re-seed your pastures on a regular basis. Most toxic plants are broad-leafed and there are effective herbicides that can be used for spot and pasture applications.
Be on watch for ornamental plantings and downed tree limbs that could have toxic implications for your horses.