Recently, one batch of grass hay was suspected of causing neurological symptoms in a horse in southeastern KY (on the border with TN). The horse was reportedly staggering and displaying a wide stance, muscle trembling and difficulty balancing. Symptoms of the animal improved after the hay was no longer fed to the animal; a similar series of events followed when another animal was fed the same hay.
The “staggers” syndrome occurs when any animal grazes or consumes hay with dallisgrass seedheads that are infected with an endophytic fungus (Claviceps paspali). Fungal spores overwinter on the ground, becoming airborne in the spring. Where unaffected seeds are light brown to tan, the spores grow sclerotia which replace the seed and turn dark brown to black. The potential for toxicity is unchanged with drying or storage, but dallisgrass hay can be less risk than pasture because some seed shatter during hay making.
Dallisgrass (a warm season grass) is not common in Kentucky, but is slowly encroaching into the area with recent warmer summers. Pastures containing dallisgrass should be
kept mowed to remove seedheads, therefore removing the risk of Claviceps paspali infections. Hay harvested from pastures containing dallisgrass should be carefully inspected for signs of infection and not fed if sclerotia bodies are found. Dr. Ray Smith believes this to be an isolated event in Kentucky and not a widespread challenge to the area. Horse and cattle owners should be vigilant to check hay and pastures regularly for the presence of dallisgrass. Since there are numerous causes of tremors and neurological abnormalities in horses, owners should contact their veterinarian immediately if they notice any animals showing neurological signs. ~ Dr. Megan Romano and Krista Lea.