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Fighting the fescue toxicity battle

Sam Strahan for Progressive Cattle Published on 26 March 2020

Much has been written about Kentucky 31 (KY-31) tall fescue over the last few decades. Most cattle producers living in the approximately 35 million-acre fescue belt (which encompasses Missouri and Arkansas, the mid-Atlantic states and most of the Southeast) understand the negative effects KY-31 tall fescue grass can have on production.

While fescue has many positive agronomic attributes including pest tolerance, an ability to withstand grazing pressure and a deep root system that helps prevent erosion on hilly terrain, chemical toxins called ergot alkaloids produced by a fungus inside the plant can negatively impact daily gains, conception rates and milk production in cattle and other species.

While many of the problems associated with fescue toxicosis are related to cattle on pasture during warmer seasons, this past year has made producing quality hay difficult. In the fescue belt, this poor-quality hay, coupled with fescue’s known negative attributes, could lead to severe complications for cow and calf health heading into spring. An article written in 2019 by Michell Arnold, an associate professor at the University of Kentucky, notes that wet weather can lead to depressed forage quality. According to Arnold, serious malnutrition in cattle was observed in Kentucky diagnostic labs in late winter of 2019. She described how low-protein and energy diets, combined with inadequate mineral nutrition, can lead to malnutrition problems.

What are the problems related to fescue toxicity?

Let’s start with the challenges that occur due to low-energy intake of the cow. Low-quality hay will have a high fiber content, which fills the gut and limits the amount a cow can consume. Toxic tall fescue can further compound the problem of inadequate energy intake, as the ergot alkaloids have been shown to slow the passage rate of feed, contributing to the “fill effect.” To prevent weight loss from inadequate energy, a cow will require supplementation from a higher-energy feed, likely either a supplement block or grain or a combination of the two.

The negative impacts of female cattle losing weight during late gestation and early lactation include reduced milk production (also exacerbated by toxic fescue, which is shown to reduce the hormone prolactin, involved in initiation of milk secretion), lower-quality colostrum and reduced conception rates at breeding. Unfortunately, that decreased milk production and low-quality colostrum will impact the calf’s health and growth for the rest of its life.

While energy is often the most limited nutrient in poor-quality fescue, protein can also be too low to meet the requirements of cows and their growing calves. Limiting the amount of protein a lactating cow has access to will reduce her milk production, affect the quality of her colostrum, and impact fetal growth and development during late gestation. If adequate protein is not provided to a growing calf (or to a growing pregnant heifer, who will have even higher protein requirements than a mature cow) frame size and muscle development will be affected, as will development of the fetus in the pregnant heifer.

The ergot alkaloids in fescue tend to reduce fescue intake, and the growth and production issues related to inadequate delivery of energy, protein and minerals are exacerbated by poor-quality hay. The challenge for many producers in late winter and early spring is to provide the requisite nutrition to the cattle herd, which will allow the cows and heifers to maintain condition, produce enough milk to feed their calves to bolster their health and growth, and be able to breed back.

In the process of conducting in vitro experiments, research has shown that a yeast cell-wall component known as modified glucomannan has a significant binding affinity for ergovaline, the most prominent fescue fungus compound. Subsequent studies of this affinity showed when cows grazing toxic fescue pastures were fed the same product, their body condition scores and conception rates improved. Similarly, when the product was fed to stocker cattle, the results included increased body weight gain. These studies illustrate that minimizing the problems created by fescue toxicity before they manifest can help animals maintain a healthier status throughout their productive lives. Most other products on the market target symptoms that appear after fescue toxicity has already affected the animal.

Low moisture supplement products, especially those containing the modified glucomannan additive, can significantly help producers in the fescue belt address the nutritional challenges of low-quality fescue forages. By providing additional protein, energy, minerals and vitamins to the rumen microbes, they help improve forage digestibility, improving livestock performance. Critical to this is overcoming such deficiencies in fescue as low copper and selenium levels, so supplements should be fortified adequately to balance the complete diet of today’s high-performing genetic animals.

As we advance our scientific understanding of fescue toxicity, new methods to combat these livestock challenges will lead to continued productivity improvements.  end mark

References omitted but are available upon request.

Sam Strahan
  • Sam Strahan

  • Account Manager
  • Ridley Block Operations
  • Email Sam Strahan

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