Beware of Grazing Tall Fescue During Hot Months

Rain in July is normally good news for pastures. But if you're grazing tall fescue, beware. Cool-season grasses usually go dormant in July, but rains this year kept grass growing. That means livestock farmers must be alert to heat stress added by toxins in the lush grass. “In this heat, remove cattle from toxic tall fescue pastures,” says Craig Roberts, University of Missouri Extension forage specialist. “Get them onto nontoxic grass with shade and plenty of water. Lush Kentucky 31 fescue in summer looks good, but is toxic,” K-31 contains a fungus between plant cell walls creating ergovaline, a toxin. That is a vasoconstrictor that cuts blood flow to body extremities, which slows cooling. Heat-stressed cattle stop eating to seek shade or to stand in a pond. “Cattle try to cool down,” Roberts says. “That is good for the cattle, but it reduces feed intake and slows gains. We had our worst gains on calves when grazing toxic fescue in a hot, wet July. Those calves gained only one-third pound per day,” Roberts says of research at the MU Southwest Center, Mount Vernon. Calves on nontoxic grass gained three times as much. The problem becomes what to do with toxic fescue left standing. Roberts says, “It makes hay, not grazing." Ergovaline breaks down when exposed to sun and air. “About a third of the toxin goes away in the first week after mowing. The toxin continues to fade in a stored bale, but at a slower rate. By winter feeding time, the toxin in hay

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One thought on “Beware of Grazing Tall Fescue During Hot Months

  1. I keep looking for a good way to positively identify K-31 fescue. Does anybody have a way to do that? I think we have some in some parts of the fields but I’m not sure.

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