“If a livestock producer calls me in the spring to ask how much nitrogen they should apply to their tall fescue pasture or hayfield, I return the question and ask what kind of fescue they have,” says Craig Roberts, extension forage specialist at the University of Missouri. “If it’s toxic Kentucky 31, I tell them to hold back. For a novel-endophyte fescue, the answer is how much nitrogen can you afford.”
In a recent University of Missouri Extension news release, Roberts explains that fertilizing toxic tall fescue with nitrogen in the spring merely compounds the problems inherent with ergovaline, the fungus-produced compound responsible for animal performance issues in toxic Kentucky 31. “With added nitrogen comes more toxin,” notes Roberts. “Effectively, the nitrogen aids both plant and fungus growth,” he adds.
“If a grower wants to apply nitrogen to increase hay yields, they need to be absolutely sure that the toxic tall fescue gets cut before seedheads emerge,” says Roberts. “Seedheads contain high levels of the toxin. Further, waiting until after heading results in low nutritional quality. It’s a double-whammy, and livestock performance will be dismal,” he cautions.
Without any effort toward mitigation, cattle forced to eat toxic Kentucky 31 fescue will have poor conception rates, reduced milk output and low average daily gains. Animals suffer extreme heat stress and constricted blood flow.
Reseeding some or all toxic tall fescue pastures with nontoxic novel endophyte varieties is an effective means of eliminating the problem. Other options include interseeding legumes into Kentucky 31 pastures to help dilute the toxic effects or by feeding supplements such as soybean hulls.