A mysterious illness has been killing horses in Kent County in the past month, but now the cause has been discovered.
Many of the cases affecting a horse's brain and nervous system have been associated with a corn-based feed, according to an announcement from the office of state veterinarian Karen M. Lopez on May 30.
Anyone using animal feed purchased in April is encouraged to contact their supplier to see if the supplier is aware of any related concerns, according to the announcement.
One of the first to report the horse deaths was veterinarian Amy L. Franklin at Country Roads Veterinary Services west of Clayton.
"We know of 16 deaths total, mostly in the Smyrna, Clayton and Camden areas," Franklin said.
She first heard of cases at the end of April.
One challenge is that the deaths are "largely contained in the Amish population and so a lot of horses aren't being seen by a veterinarian," Franklin said. "Some passed away without us hearing about it, and when they get sick they die very quickly."
The symptoms horses showed were blindness, heat butting or pressing and a lack of coordination.
While some horses have survived, most of the horses with the symptoms have died, usually quickly, Franklin said.
In one case, a client reported that the horse was acting normal one day, but the next morning was showing symptoms and later that morning was dead.
Along with notifying the Department of Agriculture, Franklin posted flyers about horse deaths at feed stores in the northwestern Kent County area to reach horse owners including the Amish. She said the Amish usually buy their horse feed at the same places as other horse owners.
Horse autopsy helps find cause of illness
Franklin talked with veterinarians at the New Bolton Center at the University of Pennsylvania School of Veterinary Medicine who asked if the owner of an affected horse could bring it to the center for an autopsy.
"A viral cause was ruled out," Franklin said. The horse tested negative for West Nile and eastern equine encephalomyelitis, two mosquito-borne viruses for which horse vaccinations are available.
"Examination of the horse's brain was most consistent with a toxin," Franklin said. "We also collected two different feed samples from farms where horses were affected and sent them out for analysis. The results of those tests showed significant levels of a mold toxin in the feed."
Requests for information from the New Bolton Center May 30 were not immediately returned as of 2 p.m., but if information is received, this story will be updated.
Tracking the source of the toxin
The office of the state veterinarian report said symptoms in horses were recorded by area veterinarians between April 22 and May 17.
Three samples of feed eaten by affected horses were submitted by the state veterinarian's office and a horse veterinarian for toxin analysis. All samples returned with levels of a fungal toxin called fumonisin. The levels in the samples significantly exceeded five parts per million, the maximum level recommended by FDA.
Fumonisin is a toxin produced by mold that grows on corn. The amount of contamination can vary due to weather during harvest and harvest periods, improper storage and other factors, according to the state veterinarian's announcement. Dry periods followed by rainfall just before and during harvest can create optimal conditions for mold growth. Insect damage and high-moisture content in storage can increase levels of toxins. Proper storage and management of corn and other feed grains are vital preventative steps.
Fumonisin can harm various livestock animals depending on the levels of contamination and the amount ingested, with horses and rabbits being most sensitive. The toxin causes softening of the brain and neurologic symptoms including lethargy, head pressing, a wobbly gait, tremoring, circling and death, according to state veterinarian's office report.
The feed samples submitted by the state veterinarian's office and the horse veterinarian had levels ranging from 31 to 101 parts per million. Safe, quality feed should not have fumonisin levels exceeding one part per million.
What should horse owners do?
Those caring for horses and other animals sensitive to the mold toxin should use these "best practices" when purchasing feed, according to the state veterinarian's office report:
Animal health questions should be directed to the Poultry and Animal Health Section of the Delaware Department of Agriculture at 302-698-4500.
Franklin said treatment options for mold toxin are limited, and so far, most cases have resulted in death.
As far as potential problems that can be prevented, Franklin encouraged horse owners to get their horses vaccinated for West Nile and eastern equine encephalomyelitis.