Use Caution When Bedding Horses on Rye Straw

Grasses including tall fescue and ryegrass, pictured here, can contain ergot bodies, which can be toxic to horses.

Photo: Courtesy Cynthia Gaskill/UK Veterinary Diagnostic Laboratory

Due to a shortage of wheat straw in the United States, more equine operations are switching to rye straw for bedding. Experts at the University of Kentucky’s (UK) College of Agriculture, Food and Environment say this is generally a good option, but there are several unique considerations when using rye straw.

Unlike wheat, where the grain is harvested first and the remaining stems are cut and baled, the whole rye plant is usually harvested and baled. This means the straw still has its seed heads, which contain awns or appendages that could cause gum irritation if the horse consumes the bedding. Thus, it’s important to watch horses bedded on rye closely to ensure their gums don’t become irritated.

Additionally, molds can develop on the stems and seed heads of rye during wet harvest conditions. As with any hay or straw, only purchase bales that are clean and dust free.

The most important consideration with rye straw, however, is the risk of ergot toxicity. Ergot alkaloids are substances caused by fungi and are poisonous to livestock—including horses—when infected cereal grasses are consumed. In horses, the most common signs are observed in broodmares and include decreased or no milk production, prolonged gestation, and fertility problems. High doses of ergot alkaloids or prolonged exposure can cause other signs in all classes of horses, such as gangrene on the extremities.

Ergot bodies resemble mouse droppings and form in the place of healthy seed of many cereal grains.

Photo: Courtesy Cynthia Gaskill/UK Veterinary Diagnostic Laboratory

Ergot fungal spores are found in the soil of much of the United States and infect the seeds of many grasses, particularly during wet springs. This infection results in the growth of sclerotia, also called ergot bodies, that look similar to mouse droppings instead of healthy seed. The sclerotia contain concentrated levels of many ergot alkaloids, a number of which are similar to the major toxin found in endophyte-infected tall fescue (called ergovaline) and cause clinical signs comparable to fescue toxicosis in mares.

Wheat straw is rarely infected with ergot because the grains are removed prior to the straw harvest. But, since most rye straw bales still contain the seed heads, ergot bodies are more likely to be present in the finished product. The good news is that ergot bodies usually fall off during the raking and baling process; however, horse owners and managers should inspect rye straw being used as bedding carefully to ensure it is free of ergot bodies. If ergot bodies are found, the straw should not be used, as it often contains toxic concentrations of ergot alkaloids.

Horse owners and managers with questions or concerns about ergotism should contact Ray Smith, PhD, forage extension specialist in the UK Department of Plant and Soil Sciences, at ukforageextension@uky.edu or 859/257-0597, or Cynthia Gaskill, veterinary clinical toxicologist at the UK Veterinary Diagnostic Laboratory at cynthia.gaskill@uky.edu or 859/257-7912. Additional information can be found at https://www.ag.ndsu.edu/pubs/plantsci/crops/pp551.pdf.

Krista Lea, MS, is research analyst and coordinator of the UK Horse Pasture Evaluation Program within the UK Department of Plant and Soil Sciences.


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