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Fescue Toxicity: Some Pros and Cons – Part III

by Wyoming Livestock Roundup

By Anowar Islam

In my last two articles, I discussed some common syndromes of fescue toxicosis in cattle. I indicated fescue toxicity can also cause serious problems in horses, especially reproduction problems in mares, including abortions, difficult birth or dystocia, longer or prolonged gestation, thickness in placenta, deaths of foal, retained placentas, little to no milk production, also known as agalactia, and even in worst scenarios, mares’ death during foaling.

 I also talked about how animals respond to fescue toxicity. This time, I will focus on biology of the causal agent.

Biology of the fungal endophyte

Previously, I discussed how the fungus living within the plant is called an endophyte. The endophyte produces ergot alkaloids, which can cause the toxicity syndromes and be highly toxic to livestock. The fungus lives within the plant throughout its entire life cycle, hence it is called endophyte. 

The fungus is not visible from the outside of tall fescue plants. Therefore, there is no difference in appearance of infected versus non-infected plants. The only way to determine the fungus presence in the plants is to do a laboratory testing.

Experimental reports suggest the endophyte is spread by seeds. So, well-managed tall fescue pastures without endophyte should remain productive without causing any toxicity problems for a long time. However, invasion of endophyte to endophyte-free pastures can occur in several ways. 

For example, it can be invaded from the introduction of infected seeds in hay or by cattle that grazed infected tall fescue within 72 hours. In general, infected plants have higher stress tolerance. As a result, pastures with low to medium levels of infection can increase infection significantly.

Reports indicate storing infected seeds under normal conditions of temperature and humidity generally results in death of the endophyte after one to two years. Hence, planting of seeds aged two years or more with endophyte-infected tall fescue can result in an endophyte-free pasture. 

However, it is cautioned weak stand may result from the old seeds as germination of older seeds generally declines with storage time.

Helpful agronomic practices

Proper agronomic practices can help reduce the incidence of fescue toxicity. It is generally recommended to plant vigorous, new crop and non-toxic seeds from clean fields to obtain the endophyte-free pastures.

I will continue discussion on fescue toxicity effects, its benefits and possible solutions, so please keep an eye on my future writings.

Anowar Islam is a professor and the University of Wyoming Extension forage specialist in the Department of Plant Sciences in the College of Agriculture and Natural Resources. He can be reached at 307-766-4151 or

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