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Pros and cons of fescue toxicity – Part VII

by Wyoming Livestock Roundup

In my last few columns, I’ve discussed common syndromes of fescue toxicosis in cattle including fescue toxicity problems in horses, reproduction problems in mares including abortions, difficult birth (dystocia), longer or prolonged gestation, thickness in placenta, deaths of foal, retained placentas, little to no milk production (agalactia), mare death during foaling, some biology of the causal agent, benefits of fungal endophyte, endophyte free tall fescue and non-toxic endophytes and their effects on tall fescue and animal performance. 

Today, I will focus on level of endophyte infection in pasture.

Endophyte testing

One important factor to keep in mind for pasture grazing is to avoid overgrazing. Overgrazing tall fescue infected with or without toxic endophyte is detrimental. In general, forage intake of animals is higher in novel endophyte tall fescue than tall fescue infected with toxic endophyte. 

It is important to manage pasture grazing by lowering stocking rates. Therefore, it is recommended novel endophyte tall fescue pasture should not be grazed below four inches.

It has been reported most tall fescue pastures are endophyte infected at a level of 60 to 80 percent. However, this infection percentage varies significantly based on initial infection level, location, time of the year and most importantly age of the tall fescue pasture.

In the pasture, not all tall fescue plants are infected by endophyte. It’s important to check and determine the infection level from time to time. When there is a concern about infection level, it is suggested to have samples and test the field. 

There are several private and public laboratories that can do the test for forage and seed endophytes. A representative sample should be collected based on the guidance provided by the testing laboratories.

Varying levels 

Often, fescue toxicity problems vary among farms although all farms might have similar or heavier endophyte infected tall fescue. This is mainly because of dilution effect of other forage species or weeds. The farms maintaining good legumes or diversity of forages have fewer fescue toxicity problems.

On the other hand, unpalatable or weed species enhances livestock to have high intake of endophyte infected tall fescue, hence increasing fescue toxicity problems. However, producers should be careful because even livestock with few visible toxicity problems might have reduced conception rates and lower calf weaning weights. This will affect the overall productivity of farms.

Also, adequate dilution may not occur evenly throughout the growing season which may result in periods when the cattle diet is mainly based on tall fescue pasture with increased risk of fescue toxicity problems.

I will continue discussion on the possible solutions of fescue toxicity problems in future columns.

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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