By David Jessee
Agronomist 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? Generally, horses naturally avoid toxic or bad-tasting plants, but watch out for some conditions. Overcrowding (less than one acre per horse) and overgrazed pastures can force grazing of plant species that are usually avoided. Poorly managed forages open the way for encroachment of toxic plants. Even if a sufficient diet of hay is fed, horses may graze toxic plants out of boredom.
Most poisonous plants are moderately toxic only if consumed alone or at certain times of the year or under conditions of heat and drought. Buttercup, Milkweed, Oaks, Walnut, Pokeweed, Dogbane, Horsetail, Perilla Mint, Johnsongrass, Jimsonweed, Nightshades and Star-of-Bethlehem are examples. Although they may be present in pastures, they're usually not consumed in amounts large enough or are diluted by grasses. However some plants are highly toxic, examples being Cherry, Red Maple, Horsechestnut, Yew, Rhododendron or Laurel. The latter three might be planted nearby as ornamentals. Low hanging or downed tree limbs that are wilted can also contain high toxin levels.
To minimize poisoning possibilities:
- Take a pasture walk to identify plants in and around the pasture that you think may be a problem.
- Don't overgraze. Allow enough desirable forage to dilute weeds that may be moderately toxic. During the summer, allow 30 to 45 day rest periods to recharge grass, and allow plants to regrow to at least 4-6 inches before grazing to recharge the plant's system. Stressed plants will die out and be replaced by weeds.
- Keep the pH adequate and keep potassium and phosphorus levels at medium, plus test soil levels to help keep grasses and legumes in the pasture.
- Newly introduced pastures to a hungry horse can cause browsing of strange plants.
- Control weeds and re-seed. Most toxic plants are broadleaves.
- Watch out for ornamental plantings and downed tree limbs.