Vermont horse owners are breathing a collective sigh of relief today upon news that the facial injuries sustained by "Nellie," a 13-year-old paint mare in Essex, were caused not by some wanton act of animal cruelty but by the animal consuming a type of clover (photo right) found throughout Vermont.
As Seven Days reported in this week's Animal Issue story, "Whoa, Nellie! Essex Equine got Burned By Unlucky Clover, Not Battery Acid," on May 16 Nellie's owners went to their barn and discovered the horse’s face covered in a gel-like substance. They assumed someone had attacked the animal with a caustic chemical that caused its skin to peel and permanently blinded its left eye.
However, a vet at Vermont Large Animal Clinic Equine Hospital in Milton later determined the burns were the result of a photosensitivity caused by the horse consuming a toxic plant: a common variety of clover that often grows in New England horse pasture called alsike clover (Trifolium hybridum), a close relative of both white and red clover, the latter of which is Vermont's state flower.
After deadline, we learned more about the toxic clover (and got these helpful pictures) from Sid Bosworth, an Extension agronomist and instructor in the plant and soil science department at the University of Vermont.
According to Bosworth, alsike clover was traditionally seeded in pasture mixes, in part because it's more tolerant of Vermont's wetter soils. Although alsike is of European origin, Bosworth refers to it as a "naturalized" rather than "invasive" species, as it's not considered a threat to native plants.
"And, it's the only clover that I know of that has that [photosensitive] trait, at least around here," he adds.
How can horse owners determine if they have alsike clover in their pasture? As Bosworth explains, the blooms look similar to white clover, the most common variety of clover found in the state, but get pink at the lower part of the flowerhead. Alsike also has two features that distinguish it from other clover: There are no hairs on it and no "watermarks" on its leaves.
Bosworth can't say for sure how much alsike is toxic to horses and other light-skinned livestock — evidently, its effects can be worse when the plant is wet — but suggests that if owners suspect their animal is having a problem, they should contact their vet. Horses are the most vulnerable, though other livestock, especially light-skinned animals, are also susceptible. Alsike is not considered harmful to humans.
Finally, the agronomist emphasizes that he doesn't want to generate a panic about this plant, especially if someone discovers some of it growing in their pasture.
"If they have a few of these out there, it's probably not a big deal," Bosworth says. "But if there's a lot of it, they may want to think about getting rid of it."
For a good list of Vermont plants that are poisonous to livestock, click here.
Photos courtesy of Sid Bosworth, UVM Ag Extension.