I want to shed some light on this topic because it most commonly affects horses in our area. Yet, it also affects cattle, which makes it essential to spread awareness going into the summer months of grazing.
Tall fescue is a cool season grass prominent in the United States. Introduced around the mid-twentieth century, tall fescue appeared well-suited for livestock grazing because of its hardiness, nutritional qualities, and ease of cultivation; however, consumption of tall fescue quickly became associated with poor animal health and performance (1).
Some symptoms of toxicity to watch for in the summer months while grazing tall fescue are excessive panting, laminitis (often mistaken for foot rot), the inability to shed their coat, and spending more time in ponds or shade. This happens because the cattle are unable to regulate their body temperature after ingesting large amounts of the tall fescue grass. Research has shown that toxicity can also cause abortions in beef cattle, but higher rates of abortions have been seen in broodmares. There has also been extensive research showing that cattle fed higher amounts of infested grass have lower daily gains, which, from a producer’s standpoint, can mean lots of money lost.
What causes this toxicity? The culprit is a fungal endophyte (Neotyphodium Coenophialum) that lives between the plant’s cells and is not visible to the naked eye. These endophytes produce an alkaloid that is toxic to cattle and horses. This same endophyte causes the tall fescue to be such a drought-hardy grass.
There is no way to eliminate this toxicity, but good pasture management can significantly reduce future problems in cattle. The endophyte-affected grass spreads by the seeds, allowing us to monitor and mow before the grass seeds out. I have seen endophyte symptoms in drought years as early as July, but in “normal” years, symptoms appear as late as September. There have been some tall fescue seed research on the potential of killing the endophytes by storing the seed in climates that kill off the fungus. That same research shows that when the fungus is eliminated, the tall fescue grasses lose their hardiness. While producers have been happy with higher daily gains in cattle, they are disappointed when the grass only lasts roughly five years.
As we see this problem more in southern states, it is common in northern states. Producers often overlook this problem, but it is essential to know if you’re having issues with cattle or broodmares while they’re out on pasture. A lot of information about tall fescue endophytes is available, so I urge all producers to be aware of the topic. If you suspect any issues in your pastures, samples can be sent in for laboratory testing to confirm. Awareness of the problem and good pasture management practices are key to prevention. ◄
(1) Bush L, Buckner RC. Tall Fescue toxicity. In: Matches AG, editor. Anti-Quality Components of Forages. Madison, WI: Spec. Pub.4. Crop Science Society