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Fescue Toxicity: Some Pros and Cons – Part II

by Wyoming Livestock Roundup

By Anowar Islam

In my last article, I discussed some common syndromes of fescue toxicosis in cattle.

Fescue toxicity can also cause serious problems in horses, especially reproduction problems in mares. These include abortions, difficult birth known as dystocia, longer or prolonged gestation, thickness in placenta, death of foals, retained placentas, little to no milk production known as agalactia and even in worse scenarios, mares’ death during foaling.

Fescue toxicity causes

It was thought for a long time, although not proven, some alkaloids such as perloline could cause the syndrome. Some scientists in 1977 at the U.S. Department of Agriculture in Georgia reported a fungus living inside the grass could be associated with the cause of the syndrome. 

More research work continued to find out the cause of the syndrome. In grazing trials in Alabama, it was shown that excellent gains and no toxicity could be obtained on tall fescue free of fungus, i.e., endophyte-free tall fescue. 

The fungus living within the plant is called endophyte. This endophyte produces ergot alkaloids that could cause the toxicity syndromes and be highly toxic to livestock.

Animal response

In general, research shows beef steer daily gains on endophyte-free tall fescue are much higher, around 50 to 100 percent, than endophyte-infected tall fescue. Typically, the daily gain is 1.5 to two pounds per day on endophyte-free tall fescue, compared to one pound or less on infected tall fescue. 

Animals on endophyte-free tall fescue are tolerant to heat, graze continually throughout the day, shed their winter hair coats in spring and are overall more active compared to animals on endophyte-infected tall fescue.

 In addition, visible signs of fescue toxicity syndrome are higher with higher temperatures in endophyte-infected tall fescue than endophyte-free tall fescue.

Beef cows also show serious negative response to fescue toxicity. These include thin and poor condition, caked with mud, spend more time in shade or water, reduced conception rate and reduced calf weight gains due to reduced milk production and consumption of toxic tall fescue. It is reported milk production of beef cows when grazing endophyte-infected tall fescue can be reduced by 30 percent or more.

Tall fescue hay and seed infected with toxic endophyte can also cause poor performance of animals. 

Generally, the toxic effect in tall fescue hay is about half the level in green grass but the effect may remain in stored hay for two years. Similarly, the stockpiled tall fescue infected with toxic endophyte can contain toxins but the level of toxicity is much lower than fresh pasture.

I will continue discussion on fescue toxicity effects and its biology, so please keep an eye out for my future writings.

Anowar Islam is a professor and 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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