Case Report: Investigating an outbreak of tremorgenic mycotoxicosis in beef cows on pasture in Mississippi due to ergot (Claviceps paspali) infection in Dallisgrass (Paspalum dilatatum)

The Mississippi State University College of Veterinary Medi­cine Ambulatory Service examined a 3-year-old Charolais-cross cow on October 19, 2023, for lateral recumbency, inabil­ity to rise and generalized tremors. Within 4 hours following initial case discovery, 20 additional cases were discovered in 2 adjacent pastures, including one mortality. Clinical signs ranged in severity from mild tremors to severe ataxia, hy­perexcitability, aggression, lateral recumbency and death. All affected cows had calved in the spring of 2023, and all 2023 spring calves were weaned 3 days prior on October 16. Overnight on October 16-17, one group of cows pushed down a fence, and 32 cows entered a pasture adjacent to their weaned calves. Following discovery of cases on October 19, all cattle were removed from the affected pasture and grass hay was provided immediately. Necropsy of 2 affected animals as well as serum chemistries of 5 affected cows revealed non-specific findings. However, abundant dallisgrass (Paspalum dilatatum) with obvious Claviceps paspali infection was present on the pasture that the cattle entered overnight on October 16-17. High-performance liquid chromatography-mass spectrom­etry (HPLC-MS) analysis of samples collected from C. paspali infected pasture as well as rumen and abomasum contents collected at necropsy revealed several tremorgenic indole di­terpene alkaloids. Additionally, DNA metabarcoding of rumen contents and forage samples confirmed the ingestion of dallis­grass infected with C. paspali. Upon recheck on October 20, all previously affected cows appeared to be recovering, and com­plete resolution of clinical signs had occurred by October 23.