by Tamara Scully

Tall fescue has earned a bad reputation. For some, it’s the grass that never dies, being an aggressive grower and having earned notoriety as difficult to eradicate. Others are concerned about its toxic effects: the ergot alkaloids which are found throughout the plant – in the highest concentrations in the seed heads – have deleterious effects on livestock.

Low or no endophyte varieties of tall fescue as well as novel endophyte tall fescue are available, but the most prominent tall fescue variety in the U.S. is Kentucky 31. K31 tall fescue is infected with a fungal endophyte and produces alkaloids, which are responsible for the plant’s toxicity to livestock. Ergovaline is the alkaloid of primary concern.

Yet the endophyte that causes the production of toxins is also responsible for the positive qualities of the forage, and the low or novel endophyte fescues sacrifice some of the good qualities by avoiding the toxins.

K31 tall fescue is a very good forage. It simply has to be managed properly to avoid its toxic effects. For many a beef producer, a hearty stand of well-managed K31 will get the herd through a rough winter with little negative effects on herd productivity.

K31 tall fescue took root during the development of the interstate highway system, happily seeding itself along roadside ditches and quickly spreading into nearby pastures and fields. This cool season bunch grass is the “most predominate forage grass in the United States,” Jeff Semler, agricultural Extension agent, University of Maryland, explained.

Endophyte Toxins

The ergot alkaloids found in K31 tall fescue produce an array of toxic effects when ingested, known as tall fescue toxicosis. Symptoms of toxicity include hyperthermia (elevated body temperature), gangrene of the extremities and reproductive issues. Other signs, such as excessive salivation, increased respiration rate and susceptibility to heat stress, are indicators of the vasoconstriction which is caused by the toxins. Ingestion of enough of the toxin can be fatal.

Subclinical signs of toxicity range from decreased average daily gain to suppressed milk production, and often visibly are noticed as the animal will have a rough coat with no shedding. These early signs of toxicity are easily reversible. They are the first indicators that there are toxins accumulating, decreasing blood flow to the skin, which eventually makes it difficult for the body to cool itself.

“If you are really observing your livestock, you should never get to that point,” Sempler said. “By removing them from the infected pasture, or supplementing, you are going to be able to mitigate a lot of that issue.”

Managing K31

Kentucky 31 tall fescue is drought tolerant, does well with wet feet and has a long growing season. It can provide a valuable forage as long as it is managed. Much of its bad reputation developed during the 1950s, ‘60s and ‘70s, when farmers were continuously grazing their cows in monoculture pastures and applying nitrogen in excess, thanks to inexpensive fertilizers. That scenario was the perfect one for K31 toxicosis.

The endophyte-infected tall fescue produces higher amounts of toxin when grown in nitrogen-rich conditions. Higher nitrogen levels increase the levels of alkaloids in the plant, which in turn produce more toxins. Continuously grazing cattle on K31 tall fescue with elevated levels of toxins is definitely not recommended. Instead, rotationally grazing cattle on fields where added nitrogen fertility is applied in a slow release method – or is simply supplied by legumes – and is not available in excess, and where seed heads are clipped and not grazed by cattle, is the proper management strategy when utilizing K31 as a forage.

The seed heads on tall fescue only occur during the first growth flush of the year, Sempler said. By controlling the timing and the degree of spring grazing, the number of seed heads produced is controlled.

“Those seed heads are where the highest amount of the alkaloid is contained,” he said.

Clipping the pasture in spring – leaving at least six inches of growth – to prevent seed head development removes the portion of the grass where the toxins are most highly concentrated. This also serves to reduce the plant’s reseeding. Because it is an aggressive grower, eliminating seed production can allow other pasture forages to take hold.

The nutritional value of K31 tall fescue is at its peak in cooler weather. Plants such as clover, orchardgrass, crabgrass, legumes and perennial warm season grasses within the pasture serve both to dilute any toxic effects of K31 and provide summer grazing when the tall fescue is least productive.

The most valuable use of K31 tall fescue is as a stockpiled forage. It not only provides nutritious winter forage, but serves as solid footing on slippery ground and can take a lot of abuse and still regenerate. Sempler recommended grazing K31 pastures in late August, then removing the cows and stockpiling the forage. After a killing frost, the pasture can provide winter grazing. K31 tall fescue can have good protein levels and is suitable for feeding dry cows throughout the winter months.

“If you’re one of those 365 grazers … you really want K31 in your toolbox,” Sempler stated.