Trade-offs in management of endophyte-infected tall fescue

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Although we are still in the middle of winter, it is never too early to start thinking about the health of your pasture.

Unfortunately, what may benefit your forages does not always benefit the grazer of those forages, especially when it comes to endophytes.

Definition

An endophyte is a microorganism that lives within a plant host but does not appear to cause disease — rather, the fungus (or bacterium) has a mutually beneficial relationship with the plant.

Many fungal endophytes are so in-tune to their plant-partner that the entire life cycle occurs inside the plant. Endophytes can improve a plant’s tolerance to environmental stresses such as drought, poor quality soil and herbivory.

In return, the endophyte receives nutrients from its “host”. In tall fescue varieties, the fungal endophyte Neotyphodium coenophialum produces ergot alkaloids that deter herbivory.

Leaf sheaths and seed heads have greater endophyte and ergot alkaloid content compared to leaf blades, which may lead to greater toxicity in these plant organs.

Research

According to the University of Missouri Fact Sheet g4669, cattle, horses, and sheep that consume endophyte-infected fescue may experience symptoms associated with ergot alkaloid toxicity that include rough hair coats in the summer, elevated core body temperatures, increased labored respiration, decreased prolactin concentrations, reduced body weight, low conception rates and offspring mortality.

Long-term exposure to tall grass fescue containing toxic endophytes may lead to fescue foot and fat necrosis.

At this time of year, endophyte toxicosis is primarily reported in horses that are fed hay. Pregnant mares experience the most serious side effects, which may include abortions when hay containing N. coenophialum is fed during the third trimester of pregnancy.

Consumption of hay with endophyte-infected fescue may delay birth of the foal, often resulting in foal mortality. Surviving foals often will have additional complications as they mature.

Mares may struggle with hemorrhaging, infection, and substantial decreases in milk production after consuming endophyte-infected hay.

Long-term issues

Long-term exposure of mature geldings to endophytes can also lower conception rates and increase the likelihood of embryonic death early in pregnancy.

To learn more about endophyte toxicosis in horses, see the University of Arkansas’ Fact Sheet 3042.

As with any disease, the first step in management is identification. How do you know if you have an endophyte problem if the organism develops inside its “host” and leaves little trace of its presence externally?

Symptoms

Unfortunately, this usually comes down to knowing what symptoms to look for in your livestock after they have already eaten a substantial amount of tall fescue.

If the symptoms occur, you may need to submit a sample of your fescue to a laboratory for verification. Management of endophytes in tall fescue will vary from pasture to pasture.

Grazing practices that encourage the choice of leaf blades over plant tissue with greater concentration of ergot alkaloids such as tillers, seed heads, and leaf sheaths may provide a reduction of endophyte toxicosis cases.

An obstacle a manager may run into, however, is that many livestock have a preference for the seed heads of tall fescue, where alkaloids may be as much as ten times as concentrated than in either the leaf blades or sheaths.

Herbicide

The use of metsulfuran-methyl (which is found in Chaparral herbicides) in tall fescue suppresses seed head development, but the trade-off with using an herbicide on forage is that can reduce available forage.

Adopting a rotational grazing system is another possible method to promote consumption of leaf blades over seed heads and leaf sheaths or avoiding ergot alkaloids altogether. Rotating cattle later in the spring to pastures with warm-season grasses can reduce the risk of alkaloid consumption.

However, more research is needed in both areas to determine timing of rotations for optimal toxic endophyte control and to identify the causal mechanism for the reduction in forage availability from herbicide use.

You may hear of diluting forage stands by increasing forage diversity as a mitigation practice. Legumes such as red clover, white clover and birdsfoot trefoil may give alternative choices for grazing.

More work may be required in the management of these forages, including frequent reseeding and inoculations. Make sure to fertilize for the legume — too much fertilizer has been shown to not only reduce legumes in a mixed stand but may also increase ergovaline, an ergot alkaloid, concentration in fescue.

Excess fertilizer may increase nutrient content in plant tissue that promotes endophyte growth and development (this also occurs with some plant pathogens too!).

When feeding livestock hay, ammoniation may be an option. Ammonia counteracts the endophyte toxicosis by breaking down plant cell walls in stems where toxins maybe found and reducing alkaloid content.

Endophytes

In addition, ammonium is a post-harvest treatment — so your fescues still see the symbiotic benefits of the endophytes. The use of novel endophytes has also been suggested as a possible management alternative used in conjunction with good grazing practices.

The idea behind these endophytes is that the plant still receives much of the benefit from the fungus (and vice versa), but these organisms produce less ergot alkaloids and are less toxic than their wild counterparts.

Endophyte-free tall grass fescue cultivars are available, but once again it comes down to the trade-off between endophyte toxicity and plant response to stress, including drought, overgrazing and pests.

Therefore management of these stands will likely be more intensive and would not provide much benefit to low maintenance pastures. Finding a management strategy that works for your pasture can help mitigate the costs associated with endophyte toxicity.

No two fields are alike, and achieving a balance between animal and forage health can make all the difference in the long-term.

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