Fescue Toxicosis in Beef Cattle
Tall fescue (Festuca arundinacea) was introduced to the United States from Europe in the 1940s because of its ability to grow in various environmental conditions. More than 90% of the tall fescue found in the United States is infected with a fungal endophyte (Neotyphodium coenophialum), which lives symbiotically with the fescue but has adverse reactions in cattle.
Richard Browning, Tennessee State University
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Cattle that graze endophyte-infected fescue suffer from three major problems: fescue foot, fat necrosis and fescue toxicity. Fescue toxicity affects the most cattle and is the most severe of the three problems. It is not a lethal condition, but it affects performance by causing heat stress, which suppresses appetite, and reduces growth and calving rates
Richard Browning Jr., Tennessee State University, told attendees of the 35th Annual Beef Improvement Federation (BIF) Meeting in Lexington, Ky., that researchers have been searching for causative agents for fescue toxicity since animal disorders were first recognized. They found that the endophyte produces many chemical compounds that are responsible for the hardiness of the plant. The ergot alkaloids are the generally accepted toxic agents of the tall fescue endophyte. There are several alkaloids present, including ergovaline, ergotamine, ergonine and ergocrystine.
Browning said that researchers found that these alkaloids are able to interact with three neurotransmitters naturally found in the bovine. These are dopamine, seritonin and norepinephrine. These alkaloids are found to affect many physiological traits the neurotransmitters affect including appetite, cardiovascular function, muscle contraction, body temperature regulation and endocrine activity.
Minimizing fescue toxicity
Browning gave several tips on pasture management to reduce the effects of fescue toxicosis, including increase stocking rates to prevent plant maturation and seeding, ammoniation of fescue hay to minimize or kill the endophyte and dilution (with other forages) or replacement of the fescue stand.
Animal management, which has been a lessor research focus, includes feed additives like seaweed extract, pharmacologicals such as ivermectin treatment, or immunologicals such as a vaccination. Research is still ongoing for any immunologicals.
Few studies have been done on breed selection for tolerance of endophyte-infected tall fescue. However, Browning says there have been research studies done on heat-tolerant and heat-sensitive cattle breeds that have shown preliminary results. The studies compare Hereford cattle, a heat-sensitive breed, and Senepol cattle, a heat-tolerant breed. The study is explained in-depth in the proceedings. Click on the proceedings link to download.
Browning concluded that cattle performance is generally dependent on two primary factors: the production environment and genetic composition of the animal. Good management of your production system will increase the profitability of your animals.
To access the audio of Browning’s presentation and the proceedings paper, visit the newsroom.
— by Stephanie Veldman