Ergot Poisoning and Dallisgrass Staggers
by Dr. John Jennings, Extension Forage Specialist
Ergot poisoning or dallisgrass staggers is a problem this summer. The rainy weather in August led to a flush of dallisgrass forage and the seedheads are commonly infected with ergot. The ergot fungus, named 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. However, ergot infection is a cause for concern and requires attention under certain circumstances.
In summer, dallisgrass seedheads are often covered in a “honeydew” exudate from the fungus that leaves a sticky film on hands and clothing after walking through fields of dallisgrass seedheads (Figure 1). As the fungus develops, it turns dark or orange from late summer to fall (Figure 2) as the sclerotia mature in the seedhead. The sclerotia drop to the soil and overwinter. When weathers warms the following summer, the sclerotia germinate and produce spores which infect dallisgrass seedheads during the blooming period.
The most common scenario of ergot poisoning occurs when new cattle are brought onto a farm that have not been exposed to dallisgrass and are turned into a field that is at the full seedhead stage. Cattle have the habit of selectively grazing seedheads which leads to a very high dosage of ergot alkaloids. 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.
Clinical signs associated with Dallisgrass Staggers involve the animal’s nervous system. In the very early stages of the disease, the only sign seen may be trembling of various muscles after exercise. As the disease progresses, muscle tremors worsen so that the animal becomes incoordinated and may show continuous shaking of the limbs and nodding of the head. When forced to move, this severely affected animal may stagger, walk sideways, and display a “goosestepping” gait. Incoordination can be severe enough that the animal will fall down when attempting to walk. 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 in scenarios where cattle are naïve to grazing dallisgrass as previously described. 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.