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

Authors: JUMPER, W - Mississippi State University; BROWN, CLARE - Mississippi State University; Lee, Stephen; Cook, Daniel; STILWELL, JUSTIN - Mississippi State University; HARVEY, KELSEY - Mississippi State University

Submitted to: Bovine Practitioner Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2024
Publication Date: 8/30/2024
Citation: Jumper, W.I., Brown, C.C., Lee, S.T., Cook, D., Stilwell, J.M., Harvey, K.M. 2024. Case Report: Investigating an outbreak of tremorgenic mycotoxicosis in beef cows on pasture in Mississippi due to ergot (Claviceps paspali) production in dallisgrass (Paspalum dilatatum). Bovine Practitioner Journal. 58(2):59-68. https://doi.org/10.21423/bpj20249035.
DOI: https://doi.org/10.21423/bpj20249035

Interpretive Summary: The Mississippi State University College of Veterinary Medicine Ambulatory Service examined a 3-year-old Charolais-cross cow on October 19th, 2023, for lateral recumbency, inability to rise, and generalized tremors. Within 4 hours following discovery of the initial case, an additional 20 cases were discovered in two adjacent pastures, including one mortality. Clinical signs in these cases 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 three days prior on October 16th. At the time of weaning, all cows (147 total) had been separated from their calves, divided approximately evenly, and placed in 5 new pastures (i.e., pastures that had not had cows in them prior to weaning). A granular, mixed trace mineral supplement was provided to these cattle free choice; however, no other hay or supplements were offered. During the night of October 16th and morning of October 17th, one group of cows pushed down a fence, and 32 cows entered a pasture adjacent to their weaned calves. Upon discovery, these cows were moved into pastures with adequate fencing over the next 24-36 hours (i.e., October 17th and 18th). Following discovery of cases in these pastures on October 19th, all cattle in the two affected pastures were moved to a new pasture and grass hay was provided immediately. Necropsy of two affected animals, one mortality and one that was euthanized due to poor prognosis, as well as serum chemistries of 5 affected cows revealed non-specific findings, precluding a definitive diagnosis. Investigation of pastures where the cases were discovered revealed no obvious cause of the observed clinical signs. However, abundant Dallisgrass (Paspalum dilatatum) with obvious Claviceps paspali infection was present on the pasture that the cattle entered overnight on October 16-17th after pushing down the fence. High-pressure 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 the presence of several tremorgenic indole diterpene alkaloids. Additionally, DNA metabarcoding of the rumen contents and forage sample confirmed the ingestion of Dallisgrass, and that the forage was infected with C. paspali. Upon recheck on the morning of October 20th, all previously affected cows appeared to be recovering. Over the next 72 hours, clinical signs continued to resolve. Complete resolution of clinical signs in all affected animals had occurred by October 23rd.

Technical Abstract: The Mississippi State University College of Veterinary Medicine Ambulatory Service examined a 3-year-old Charolais-cross cow on October 19th, 2023, for lateral recumbency, inability to rise, and generalized tremors. Within 4 hours following discovery of the initial case, an additional 20 cases were discovered in two adjacent pastures, including one mortality. Clinical signs in these cases 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 three days prior on October 16th. At the time of weaning, all cows (147 total) had been separated from their calves, divided approximately evenly, and placed in 5 new pastures (i.e., pastures that had not had cows in them prior to weaning). A granular, mixed trace mineral supplement was provided to these cattle free choice; however, no other hay or supplements were offered. During the night of October 16th and morning of October 17th, one group of cows pushed down a fence, and 32 cows entered a pasture adjacent to their weaned calves. Upon discovery, these cows were moved into pastures with adequate fencing over the next 24-36 hours (i.e., October 17th and 18th). Following discovery of cases in these pastures on October 19th, all cattle in the two affected pastures were moved to a new pasture and grass hay was provided immediately. Necropsy of two affected animals, one mortality and one that was euthanized due to poor prognosis, as well as serum chemistries of 5 affected cows revealed non-specific findings, precluding a definitive diagnosis. Investigation of pastures where the cases were discovered revealed no obvious cause of the observed clinical signs. However, abundant Dallisgrass (Paspalum dilatatum) with obvious Claviceps paspali infection was present on the pasture that the cattle entered overnight on October 16-17th after pushing down the fence. High-pressure 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 the presence of several tremorgenic indole diterpene alkaloids. Additionally, DNA metabarcoding of the rumen contents and forage sample confirmed the ingestion of Dallisgrass, and that the forage was infected with C. paspali. Upon recheck on the morning of October 20th, all previously affected cows appeared to be recovering. Over the next 72 hours, clinical signs continued to resolve. Complete resolution of clinical signs in all affected animals had occurred by October 23rd.