Watch for fescue toxicosis this grazing season
Livestock producers who graze fescue pastures should always have fescue toxicosis in mind. Tall fescue is a cool-season, high-quality perennial grass that thrives in moderate temperatures with adequate rainfall. Fescue has a long growing season, and it is insect and nematode resistant, but it can also be noxious to livestock.
Fescue toxicosis, is caused by ergot alkaloid toxins, and specifically ergovaline, produced by the endophyte fungus Neotyphodium coenophialum.
“This fungus benefits the plant by warding off herbivores by making them sick, and also helps prevent attack from insects,” said Matt Poore, ruminant nutrition Extension specialist at North Carolina State University.
Cattle and horses are commonly affected by this condition, and although it is not known to kill them, the symptoms of the condition often lead to cattle culling. Poore said the toxin is highest in the late spring and early fall. Symptoms range from lameness, tissue necrosis, gangrene, heat stress, reduced feed intake, reduced milk production, and weight loss.
Effects of fescue toxicosis
“When animals eat the grass, they have a condition called vasoconstriction where the blood vessels will not expand to increase blood flow to the surface of the animal, helping them cool off,” Poore explained. “They also suffer from the suppression of the hormone prolactin, which can interfere with the initiation of lactation, and the shedding of the winter hair coat. The hair coat shedding problems and the vasoconstriction make animals very susceptible to heat stress, resulting in lower feed intake, slow growth rate, and poor reproductive performance.”
Poore said growing animals with fescue toxicosis usually experience very slow growth rates, and breeding animals will have a low body condition score, leading to reduced breed-back rates.
“First-calf heifers are especially prone to ‘agalactia’ meaning they have no milk,” Poore said. “There is a range in how tolerant animals are, so in most herds there will be some cows that are very dramatically impacted—usually young cows, while others will have very few symptoms.”
Some key indicators an animal grazing fescue has fescue toxicosis is if they are standing in water, staying in the shade when it is not hot outside or wallowing in mud to cool off, he said.
“The best test of if you have a problem is to check animal behavior during late spring,” Poore said. “If there are cows that are slow to shed winter hair, if reproductive rate is low, if animals stand in the pond during a not so hot day, or if animals are muddy and rough, and look like they feel bad, you have it.”
Managing the condition
Removing the animal from fescue is the best course of treatment to stop the toxicosis, and Poore said livestock should have no lasting effects from it. Producers can also reduce toxins in the grass by clipping seed heads—where the highest levels of toxins exist—and limiting fertilizer use—which increases toxin levels.
Poore said feeding concentrate supplements is also a tactic to reduce toxins. Grass can be tested by sampling individual plants to analyze for the fungus.
“Renovating pastures and planting Novel Endophyte Tall Fescue provides the advantages of the toxic fescue from a pasture growth and vigor standpoint, while maintaining animal performance because the Novel Endophyte included with the seed is one that does not produce ergovaline,” Poore said. “This is the long-term approach that many progressive cattlemen are taking across the tall fescue belt.”
Poore said there is ongoing research to identify and reproduce highly tolerant animals that have a genetic advantage while grazing fescue.
“This is slow, but there is some progress being made with the Slick Hair Gene present in Senepol cattle and other tropical breeds from the Americas,” he said.
Lacey Vilhauer can be reached at 620-227-1871 or [email protected].
