LSU Vet Med plays major role in detecting toxin affecting Louisiana horses


Discovered Clostridium toxin found in alfalfa cubes was causing serious illness and even death in horses

The Louisiana State University (LSU) School of Veterinary Medicine played a significant role in diagnosing and treating several horses in Louisiana infected with Clostridium botulinum type C, which causes botulism. They discovered that alfalfa cubes were infected with the toxin that originated from one source and were sold in various states, with horses in Louisiana, Texas, Colorado, and New Mexico reportedly falling ill and many even dying from the toxin.

Clostridium botulinum type C bacteria affecting the horses in Lousiana (Photo courtesy of LSU Vet Med).

Clostridium botulinum type C bacteria affecting the horses in Lousiana (Photo courtesy of LSU Vet Med).

According to the university release,1 “botulism is a rare but serious illness caused by toxins released by a bacteria. That toxin then binds to nerves that affect muscles throughout the body and causes difficulty breathing, muscle paralysis, and even death.” The toxin that causes Type C Botulism usually is ingested from contaminated feeds and binds to nerve receptors. After this happens, it cannot be reversed, however, if it’s discovered early, an anti-toxin can be used to keep free, unbound toxins from binding to the nerve receptors.

On December 3, 2022, a horse from a breeding farm in Vermilion Parish came to the LSU Veterinary Teaching Hospital and was seen by the equine emergency service, and a second horse came the following day; both were presenting with neurological issues. The horses were tested for infectious agents, including Eastern Equine Encephalitis, West Nile virus, herpes virus, and rabies. On December 5, additional horses from the same farm arrived with the same symptoms. In total, LSU saw 15 horses, while others were treated at the farm, with about 20 horses in Louisiana suffering from the toxin.1

The first round of horses was treated by Mustajab Mirza, DVM, DACVS, associate professor of equine surgery. Then, Rose Baker, BVMS, DACVIM (LAIM), assistant professor of equine medicine, took over the care of the horses. On December 6, Matthew Welborn, DVM (LSU 1987), MPH, DACVPM, professor of food animal health maintenance at LSU Vet Med; and Christine Navarre, DVM (LSU 1990), DACVIM, professor of veterinary science, visited the farm in search of potential toxins.

The initial suspicion was that the horses had been exposed to a toxin on the property. Because Welborn and Navarre did not find an obvious source of contamination, they recommended additional testing of the feed with a request made to the Louisiana Department of Agriculture and Forestry (LDAF). Baker collaborated with Jonathan Roberts, DVM, director of the commercial feed program with LDAF, to identify the cause of the illness and its source. All of the affected horses in Louisiana originated from the same breeding farm; though it was possible that other horses in Louisiana were affected and those horse owners attributed illness and/or death to another cause.

Roberts teamed up with farm and LSU to set up testing of alfalfa cubes. Official samples were sent both to the Food and Drug Administration (FDA) and the California Animal Health and Food Safety Laboratory at the University of California, Davis School of Veterinary Medicine, which revealed a positive result for Clostridium botulinum type C. While UC Davis was testing the cubes, the Louisiana Animal Disease Diagnostic Laboratory (LADDL) at LSU Vet Med, and Baker, tested other samples from patients for botulism.1 Additionally, LADDL performed necropsies on 12 horses with additional toxin testing to further find the cause of death.

So far, LSU Vet Med has successfully treated 5 horses and sent them home and is still currently treating 2 horses. These horses came in on an emergency basis and were triaged and because of herd outbreak concerns, various diagnostic tests and intensive nursing care were required immediately. Management of the ill horses required round-the-clock care, and a committed nursing staff and veterinary students.

On December 17, 2022, the USFDA issued a warning2 regarding recalled lots of alfalfa cubes that seemed to have caused illness and death in horses. At this time, the FDA reported that horses in Louisiana, Texas, New Mexico, and Colorado have displayed neurological signs that may be associated with the toxin found. An updated advisory3 on January 5, 2023, the LDAF released confirmed the cause of the illness and death to be botulism. Thanks to the tremendous efforts of farm owners and staff, LSU Vet Med, LADDL, LDAF, UC Davis, and the FDA, they got to the root of the issue quickly.

If you believe that your horse has been affected, contact your veterinarian immediately or the LSU Veterinary Teaching Hospital at 225-578-9500.


  1. LSU Vet Med instrumental in identifying toxin affecting Louisiana horses. News release.Louisiana State University College of Veterinary Medicine.January 11, 2023.Accessed January 12, 2023.
  2. FDA cautions horse owners not to feed recalled lots of Top of the Rockies alfalfa cubes due to reports of illness and death. News release. US Food and Drug Administration. December 17, 2022. Accessed January 12, 2023.
  3. FDA confirms Clostridium Botulinum type C was found in alfalfa hay cubes tied to the death of multiple horses in Louisiana. News release. State of Louisiana Department of Agriculture and Forestry. January 6, 2023. Accessed January 12, 2023.
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