Dealing with toxic fescue
by Sally Colby
The Alliance for Grassland Renewal partnered with several state universities to present several day-long workshops on novel tall fescue renovation. At a workshop held recently in Maryland, Dr. Craig Roberts, University of Missouri, discussed some of the animal health problems associated with tall fescue. “Fescue toxicosis is a very serious problem,” he said. “When calf prices are really low, losses are close to $160 million but probably more like $240 million.”
Kentucky 31 tall fescue (also referred to as toxic fescue) has been a pasture staple since the 1940s. Its vigorous root system, bunch growth habit and long growing season made it suitable for erosion control. It tolerates both drought and flooding, withstands heavy grazing and is suitable for reserve grazing. The traits that make tall fescue stand up to adverse conditions are present thanks to a fungal endophyte within the plant itself. However, this endophyte produces ergot alkaloid compounds, notably ergovaline, which are harmful to livestock.
Roberts explained one common problem with toxic fescue – vasoconstriction. “It’s narrowing of the blood vessels, so the animal can’t control its internal temperature,” he said. “Blood isn’t circulating, so in winter, blood doesn’t reach extremities. Cattle are too cold in winter and too hot in summer.”
For beef cattle, another major issue is low feed intake that results in low rate of gain, low birthweights and low weaning weights. “In worst case scenarios, calves are losing 112 pounds,” said Roberts, sharing research results. “In the best case, they’re losing 56 pounds. There are also problems with low pregnancy rates and low milk production.”
Cattlemen are familiar with the lameness (also known as fescue foot) associated with toxic fescue. “Many people say they don’t have a fescue toxicosis problem because there’s no lameness,’” said Roberts. “But you can’t always see low rate of gain.”
In one study, steers in Virginia gained 1.06 lbs./day on “hot” fescue but gained 1.47 lbs./day after being moved to novel fescue. In North Carolina, steers gained 0.55 lbs./day on hot fescue and 1.65 lbs./day on novel fescue. Calving rate on toxic fescue was about 55%, but when animals were moved to non-toxic fescue, the calving rate reached 95% or higher.
As Kentucky 31 became popular as a mainstay forage, cattlemen became more aware of the problems it caused. In 1977, scientists identified the toxic organism, an endophyte, that grows in tall fescue between plant cells. In the 1980s and ‘90s, endophyte-free fescue varieties were released. Animals thrived on this new fescue, but it didn’t persist and had to be replanted.
Realizing that the fescue plant required an endophyte to maintain its beneficial traits, scientists inserted a strain of endophyte that didn’t produce toxins. The new endophyte-infected fescue, known as novel tall fescue, proved to be drought resistant, non-toxic to animals and persisted in pastures.
Today’s farms with tall fescue may have one or more fescues: Kentucky 31, which is infected and toxic; endophyte-free fescue, which is non-toxic but doesn’t persist; or novel endophyte, which is infected but not toxic. Any fescue can be tested for endophyte levels, and low infection may not create problems. But Roberts says once the level reaches 60% infected, problems begin and a management plan should be initiated.
Dr. Amanda Grev, Extension specialist in forage and pasture at the University of Maryland, offered tips on managing existing toxic fescue pastures. She noted numerous folk remedies to manage fescue toxicosis but cautioned cattlemen that none are effective. Instead, understand when the plant is most toxic and focus on points of control.
The first strategy is to dilute the pasture with other forage species such as smooth bromegrass, orchardgrass, red clover, white clover or birdsfoot trefoil. “Animals are likely grazing preferred non-toxic species much more heavily than grazing the toxic Kentucky 31,” said Grev. “Be careful in managing the stand to keep the non-fescue species thriving.”
Another strategy is to rotate animals to different pastures. Ergovaline (the toxic compound) concentration in fescue varies throughout the year, so avoid grazing toxic fescue from spring into early summer – that’s the time to use winter annual forages, then use summer annuals from late summer into autumn. “The highest concentrations of alkaloids are in the seedheads,” said Grev, “so one option is to clip the pasture prior to the plant forming viable seeds to stop seed production and lower the total concentration of toxins in the plant.”
A broadleaf herbicide such as Chaparral helps suppress seedhead production in tall fescue, but be aware that such treatment will also eliminate clover. Spraying should be done at boot stage, prior to seedhead development in spring. Studies on treated fescue show improved weaning weights, rate of gain and pregnancy rates as a result of minimizing seedhead production and lowering ergovaline concentration.
One of the strong points of Kentucky 31 is its ability to produce high-quality stockpiled forage suitable for winter or early spring grazing. “The key is that ergovaline concentration decreases throughout winter,” said Grev. “As we’re stockpiling fescue, even as we go from the early stockpile period and into January, February and March, ergovaline concentrations are decreasing in the plant. The key to stockpiling is to use it later, or last.”
Because nitrogen increases the alkaloid concentration in the plant, limiting nitrogen application helps decrease toxicity. Grev explained that to prior to understanding the alkaloids in toxic fescue, the problem was thought to be poultry litter application. However, further studies showed increased toxicity was due to the nitrogen content in poultry litter, not the poultry litter itself.
Although it isn’t a common practice, ammoniating hay helps reduce toxicity. The process involves weighing and stacking hay, covering with heavy plastic and burying the edges, then treating with anhydrous ammonia at 3% on a per weight basis. Ammoniated Kentucky 31 fescue hay has the lowest ergot alkaloid concentration compared to green chop, silage or dry hay.
Supplementing the diet can also help reduce toxicity from fescue. The goal is incremental alleviation, so if cattle are grazing toxic fescue, legumes can be added to dilute the pasture. Moving cattle to different paddocks that don’t contain toxic fescue with non-fescue forage is also beneficial.
“The goal in managing toxic fescue is to use a combination of different strategies to incrementally alleviate reduced daily gains from toxic fescue,” said Grev.
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