Fescue Toxicity

If you are grazing, you are always looking for a forage that produces high yields, good quality, and seasonal longevity. Tall fescue is a forage that can provide a high yield and longer grazing season. This cool-season forage is drought tolerant and grows in a wider range of temperatures, which generally results in high yields. Many pasture mixes will include tall fescue, because of its ability to rapidly produce forage. There are a few drawbacks to utilizing a tall fescue stand; however, if you can identify tall fescue, you can better manage that forage stand for the future.

Tall fescue can be identified by its dull upper surface and its shiny underside. The veins on the leaf are very distinct (Figure 1). Auricles are usually blunt and hairy (Figure 2). Tall fescue also has a low ligule (Figure 3). The seed head is an open panicle with 5 to 9 florets per spikelet (Figure 4).

Figure 1: A tall fescue leaf has very distinct veins, a dull upper surface and a shiny underside. Image credit: Dave Hartman, Penn State Extension.

Figure 2: The auricles on tall fescue are blunt and hairy. Image credit: Leanna Duppstadt, Penn State Extension.

Figure 3: The ligule on tall fescue is very low, almost non-existent. Image Credit: Leanna Duppstadt, Penn State Extension.

Figure 4: A tall fescue seed head is an open panicle with 5 to 9 florets per spikelet. Image Credit: Leanna Duppstadt, Penn State Extension

One drawback to tall fescue is palatability. Cattle tend to avoid consuming tall fescue, because it is a more course and fibrous forage. Animal gains tend to be lower on these fields but are a good source of forage for the beef cow herd. When cattle are turned out to graze a fescue mixed stand, the cattle will eat around the less palatable fescue. Tall Fescue outcompetes other forages, so less grazing pressure will lead to a purer stand of tall fescue. Grazing at a higher intensity and a shorter time period will force cattle to graze more evenly, which can help manage this forage in an existing stand. Winter stockpiling or grazing forage over the winter months, also known as extending the grazing season, is another attractive characteristic of tall fescue.

The biggest issue with tall fescue is toxicosis. Endophyte-infected tall fescue produces ergot-alkaloid compounds, which can be a life-threatening toxin within the plant. Although the toxin can cause issues in cattle all year round, the biggest issues tend to stem to the summer months. Ergot-alkaloid toxicity leads to constricted blood flow that interferes with the animal's ability to regulate body temperature. Otherwise known as heat stress or cold stress. Some other symptoms of fescue toxicosis can include fever, tachypnea, or rapid breathing, rough hair coat, excessive salivation, lameness, poor reproductive success, and increased water intake.

Not all tall fescue is endophyte-infected. The notorious tall fescue variety that gives fescue a bad name, is Kentucky 31; however, there are other varieties that are endophyte-free and novel endophyte-infected tall fescue. The endophyte-free variety does not have endophytes included in the plant, and novel endophyte-infected tall fescue has a modified endophyte that does not produce the ergot alkaloids that cause fescue toxicosis but still gives tall fescue the hardy traits it is known for. Many times, reseeding with these other varieties is a temporary fix, because cattle will prefer the other tall fescue varieties over the Kentucky 31 variety. This grazing selection gives Kentucky 31 the chance to out-compete the other varieties.

A way to mitigate fescue toxicosis is not grazing tall fescue when temperatures are above 75 to 80 degrees Fahrenheit, and do not fertilize a Kentucky 31 stand with high nitrogen fertilizer. Another way to manage a Kentucky 31 stand is through interseeding a clover into the stand. By adding a clover, nitrogen will be fixed throughout the season rather than a bunch of nitrogen being added all at one time by adding fertilizer. In this situation, the solution to pollution is dilution. If you add a clover to the field, the cattle now are consuming a forage other than just ergot-alkaloid infected forage; thus, diluting the amount of toxin consumed. When tall fescue reaches maturity, the endophyte levels are highest in the seed panicle. Removing the seed head can help prevent fescue toxicosis. Stockpiling forage for winter consumption can also decrease the risk of fescue toxicosis.

If you are not interested in managing through the Kentucky 31 variety, eliminating the variety can be an option, if done correctly. Note, tall fescue is a persistent forage, which is why historically tall fescue is included in grazing mixes. One method to eliminate tall fescue is by spraying an herbicide in the spring, reseeding a summer annual, spraying again at the end of the summer annual's growing period, then reseeding with a desired pasture mix with a winter annual or oats. This combination will help suppress weeds and fescue growth until the new stand is established. Another method could be spraying near the end of summer, letting any regrowth of tall fescue to grow, respraying, then reseeding with a desired pasture mix with a winter annual or oats for weeds and fescue suppression.

The key is to identify the forages that you have, be aware of some of the symptoms, and manage the stand. If you have tall fescue, more specifically endophyte-infected fescue, do not think your pasture is worthless. You have options on how to manage or reseed that pasture for a successful future.

Disclosure: This presentation including its text, graphics, and images, is for educational purposes only; it is not intended to be a substitute for veterinary medical advice, diagnosis, or treatment. Always seek the advice of a licensed doctor of veterinary medicine or other licensed or certified veterinary medical professional with any questions you may have regarding a veterinary medical condition or symptom.