It wasn't the water.
It wasn't the hay.
It wasn't inattention or reckless disregard by caretakers.
No communicable disease was running rampant.
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But something has suddenly killed three horses on Camelot Farms and left another critically ill.
Now, owners Mark and Anne Kennedy think they have found the problem.
They sent a sample of horse feed the farm used to the Diagnostic Center for Population and Animal Health at Michigan State University. Tests there came back positive for monensin -- a supplement used in cattle feed that is poisonous to horses.
The Kennedys on Tuesday declined to release the name of the feed manufacturer.
About 20 horses are boarded at Camelot Farms in addition to the Kennedys' 22 horses.
On Dec. 14, one boarder's horse and another that belonged to the Kennedys began showing colic symptoms, an indication of a serious gastrointestinal problem. With quick treatment, those symptoms can subside.
But the two horses deteriorated quickly and were taken to the Edisto Equine Clinic the following day. They were dead within 72 hours.
On Dec. 17, another boarded horse began showing the similar colic symptoms.
That horse died two days later, on Dec. 19.
The Kennedys worked feverishly to figure out what was wrong.
"It's torn my heart apart," Anne Kennedy said.
They called Adam Eichelberger, director of animal health programs at the Clemson Livestock Poultry Health Programs. He came to investigate, the Kennedys said. For privacy reasons, Eichelberger could not confirm he visited Camelot Farms. He did confirm that he recently visited a farm in Beaufort County and found no reason to be concerned about a disease outbreak or maltreatment.
Necropsies of the horses came back negative for any disease.
The Kennedys implemented a self-imposed quarantine at the farm. No one was allowed to come or go. They canceled trail rides and lessons. They sent the hay off for testing. It came back clean.
Thinking the water might be contaminated, the Kennedys purged the farm's well and ran 1,375 feet of hose to get city water. They replaced all the water buckets and disinfected the barns and feed buckets three times.
The Michigan State test results at least gave the Kennedys an answer.
It did little, though, to lift their spirits.
Anne Kennedy hasn't had a solid night's sleep since the first horse died, she said.
She lays down, exhausted, and wakes up crying in the middle of the night. She gets up to check on the horses often and runs through a mental checklist of what she's done and what she could have done wrong.
Then she lays back down, and the cycle begins again.
"I swear I've aged 100 years," Anne Kennedy said Tuesday.
Her speech speeds up as she explains the last two weeks of her life -- the heartbreak and helplessness she's felt with each sick horse.
The thought of another dying sends her into an even darker spiral.
On Tuesday, Mark Kennedy took another one of their horses, Oopsie, to the University of Georgia's veterinary clinic in Athens. The horse is exhibiting the same colic symptoms as the others, and the Kennedys fear she will die soon.
The sadness Anne Kennedy feels has an undertone of anger as well.
"You open up a bag a food, and you don't expect it to have poison," she said.
The Kennedys have continued to be in contact with all the boarders. None have accused them of negligence, and many have come to help. They volunteer to disinfect the farm's equipment, administer medicine and fluids and have even cleaned the Kennedys' home.
"It's a real family here," said Ellen Hudson, who boards her two horses at Camelot Farms. "We're here all day and night to help in any way we can. You'll never meet anyone who cares more than Anne and Mark do."