buttercups in horse pastures

The University of Kentucky (UK) Horse Pasture Evaluation Program has had several calls regarding the safety of yellow buttercup in horse pastures. As such, Megan Romano, PhD, veterinary toxicology resident, described on the plant’s potential risks to horses.

According to the current U.S. Department of Agriculture PLANTS database, Kentucky is home to nearly 30 different species of Ranunculus, or buttercups. Ranunculus leaves, flowers, and stems have a sharp, pungent taste, and livestock generally avoid grazing the plants.

Some Ranunculus species contain ranunculin, a compound hydrolyzed to protoanemonin when the plants and cells are damaged (for example, when they’re chewed). Protoanemonin is a vesicant (an agent that causes skin, mouth, and digestive system blistering). Those Ranunculus species with the highest ranunculin concentrations are the most toxic.

Plant cell damage also occurs when buttercups are cut and dried in hay. Ranunculin hydrolysis (when a compound breaks down chemically due to reaction with water) to protoanemonin likely occurs as the plants dry. Protoanemonin then forms anemonin, another bioactive compound which is not a vesicant. Dried Ranunculus plants, therefore, are expected to lose toxic potential fairly rapidly, although scientists haven’t studied and published research to specifically confirm this.

Buttercups can cause mouth pain and blisters, drooling, oral and gastric ulcers, colic, and diarrhea. Horses are one of the most sensitive species to Ranunculus’ gastrointestinal effects. These effects can be severe if horses ingest buttercups in large quantities, but their acrid taste usually deters further grazing. Clinical signs are typically seen only in animals forced to consume buttercups when they have nothing else to eat.

A few anecdotal reports have suggested an association between the presence of Ranunculus species in the pastures and abortions in cattle and horses; these reports are unconfirmed, however, and attempts to reproduce the disease have been unsuccessful. Bur buttercup (Ceratocephalus testiculatus) can cause significant illness, but this plant occurs primarily in the Western U.S. and is not a true buttercup, as it belongs to a different genus.

All in all, the risk posed by Ranunculus species in Kentucky appears minimal if there are plenty of other forages present; animals avoid grazing the unpalatable fresh plants, and the dried plants appear to be much less toxic.

A review of UK Veterinary Diagnostic Laboratory records over the last 13 years revealed no cases of livestock deaths attributable to Ranunculus. It is possible, however, that cases of colic or diarrhea have unknowingly were caused by Ranunculus ingestion but never attributed to the plant.

Preventing Toxicosis

Buttercup toxicosis poses the greatest risk to starving animals with nothing else to eat; this can be easily prevented by providing animals with adequate forage. Because animals avoid grazing Ranunculus, it proliferates in overgrazed pastures. Overgrazing can be prevented by maintaining appropriate stocking rates.

Ray Smith, PhD, UK forage extension specialist, said it’s too late this year to spray to kill yellow buttercup. But maintaining good grass cover prevents many weeds, including buttercup, from germinating in fall or winter. Resting pastures and not overgrazing are key to improving pasture health.

Thin stands with bare patches or areas with summer annual grasses, like crabgrass, can be overseeded with a pasture mix in September. Be sure to soil test every two to three years and apply amendments based on soil test recommendations. In most horse pastures, nitrogen is most beneficial in the fall to improve root density and thicken stands.

Additional information on buttercup in pastures and control methods can be found in an article published in Forage News; read Buttercups in Graze Pastures at kyforagenews.com/2018/01/31/buttercups-in-grazed-pastures/.

Megan Romano, PhD, veterinary toxicology resident at UK’s Veterinary Diagnostic Laboratory; Ray Smith, PhD, forage extension specialist within UK’s Department of Plant and Soil Sciences; and Krista Lea, MS, research analyst and coordinator of UK’s Horse Pasture Evaluation Program, provided this information.

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