Arkansas’ rainy summer has been a boon for Dallisgrass, but with that bounty comes a higher danger that grazing cattle can be poisoned by a fungus that’s common to that type of grass, said John Jennings, professor-forage for the University of Arkansas System Division of Agriculture.
The ergot fungus, Claviceps paspali, infects the flowers of Dallisgrass and the growing fungus replaces the seed. The fungus only affects seedheads – the other parts of the plant are nontoxic. Ergot poisoning occurs to a limited extent each year in Arkansas, but is more prevalent following summer rainy periods. Dallisgrass is very common in the southern half of Arkansas and grows in low moist soils.
“Forage quality and palatability are very good for most grazing livestock,” he said. “However, ergot infection is a cause for concern and requires attention under certain circumstances.”
The most common scenario of ergot poisoning occurs when cattle not previously exposed to Dallisgrass are turned into a pasture when the grass is at full seedhead.
“Cattle have the habit of selectively grazing seedheads, which leads to a very high dosage of ergot alkaloids,” Jennings said. “Even on farms where cattle are previously exposed to dallisgrass, poisoning can occur when animals are hungry and are turned into a field full of seedheads. Symptoms are much less common in herds exposed to dallisgrass in mixed grass pastures.”
Ergot poisoning affects the cattle’s nervous system.
“In the very early stages of the disease, the only sign seen may be trembling of various muscles after exercise,” he said. “As the disease progresses, muscle tremors worsen so that the animal becomes uncoordinated and may show continuous shaking of the limbs and nodding of the head.
“When forced to move, the severely affected animal may stagger, walk sideways, and display a ‘goosestepping’ gait,” Jennings said. This late stage gave rise to the name “Dallisgrass Staggers.”
Some animals may be found down and unable to stand. Diarrhea may be noted in some affected animals. Death can occur in severe cases, especially to cattle unused to Dallisgrass.
There is no cure for ergot poisoning, but removing cows from infected pastures when symptoms are first noticed usually results in uneventful recovery in three to five days. Clipping seedheads to prevent animals from grazing them helps prevent the problem from occurring. Ergot toxicity from dallisgrass hay is very uncommon since the total intake of hay forage dilutes any ergot contained in the hay.
The fungus turns orange or rust colored from late summer to fall as its spore-like sclerotia mature in the seedhead. When the weather warms the following summer, the sclerotia germinate and produce spores that infect dallisgrass seedheads during the blooming period.