A deadly mystery

When all but one horse at a Virginia boarding stable develop liver disease, a veterinary turns detective to discovery the cause: panicum toxicosis

Ninety-Nine was the first horse to die. But initially the mare’s illness seemed like nothing more than mild colic. It began on a Sunday in November 2204 when Ninety-Nine, one of the 15 horses at Triple J Farm in Virginia, started to show signs of digestive upset.

Melinda Freckleton, DVM, of Haymarket Veterinary Service, was called to the farm and found Ninety-Nine standing quietly but looking uncomfortable and occasionally glancing at her sides. The mare’s respiratory and heart rates were slightly elevated. More worrisome, however, was the slight impaction Freckleton felt when she palpated the mare.

Before leaving for other emergency calls, the veterinarian gave Ninety-Nine intravenous Banamine and instructed the owners to offer the mare one small flake of hay for each manure pile she produced. Freckleton also told them to call if the mare’s condition worsened. At about 6 p.m., the owners reported that Ninety-Nine was lying down in front of the barn, an active area at the busy stable, and seemed oblivious to her surroundings.

Freckleton hurried back to the farm, certain that something serious was wrong. But she was puzzled: A colicky horse would be restless an in obvious pain rather than lethargic and unresponsive. Deciding she needed help in diagnosing the problem, Freckleton referred the mare to the Marion DuPont Scott Equine Medical Center in Leesburg, Virginia.

At the center, Ninety-Nine developed severe diarrhea. She also began showing signs of liver disease, including jaundice—yellowing of the skin and sclera caused by a buildup of a protein (bilirubin) normally removed from the blood by the liver. The mare was treated aggressively but got progressively sicker until she was euthanatized six days later. A postmortem examination showed extensive damage to her liver, but did not reveal the cause.

More trouble

Two weeks later, one of Freckleton’s colleagues mentioned that she was headed out to Triple J Farm to treat a mild impaction colic. The odd thing was, this was the second case at Triple J in as many days, she said: “I don’t understand what’s going on there.”

Freckleton stopped short. This was the same stable and the same problem she had handled. She mentioned this to her colleague, who hadn’t heard about the previous case, and offered to go along on the call.

At the farm, the two veterinarians examined two horses with signs similar to Ninety-Nine’s and took blood samples. Both horses were depressed and jaundiced. They also had hemorrhages under the gums and unusually smelly breath. Freckleton and her colleague looked for colic risk factors at the farm but found none–the troughs at the stable were full of fresh water and the hay looked fine. Knowing how quickly Ninety-Nine’s condition deteriorated, the veterinarians rushed the blood samples to the DuPont Scott Center for analysis. The results, which came back the next day, showed significant elevations of substances normally filtered by the liver: Both horse had liver failure. Freckleton immediately pulled blood samples from the other horses at the farm and sent them off for analysis. The lab report was both surprising and disturbing: All but one of the horse had abnormalities that suggested impaired liver function. Three days later Freckleton called a meeting of the owners. “It was the hardest thing I’ve ever done as a veterinarian,” she said. “I had to tell people their horses were sick and we didn’t know why—and the only case we knew about had died.”

Gathering evidence

In early December, veterinarians and technicians from the DuPont Scott Center made a rare farm call, setting up a special clinic at Triple J to take liver biopsies from the 14 horses stabled there. Each horse was sedated and a special long, hollow needle was inserted between two ribs and directed into the liver. The results confirmed liver damage in all but one horse.

The veterinarians requested a total lockdown at Triple J Farm. Every horse stayed in his stall. Doors were closed. There was no turnout. Every variable was scrutinized and controlled.

A toxin of some sort was an obvious possibility. Paddocks were searched for poisonous plants, but none were found. The veterinarians took blood samples from the farm cats and dogs to rule out tainted well water, and the tests came back clean.

Grain was eliminated as the culprit because each horse had been on a different ration. Nevertheless, all of the horses were put on a liver-friendly equine senior feed. In case there as a problem with the farm’s hay, the stable owners shipped in a load of new timothy from out of the area and packed the old hay into storage.

Freckleton also scoured the research literature for clues and consulted with experts far and wide, including equine liver disease specialist Tom Divers, DVM, one of her former professors at Cornell University.

“This isn’t something any of us see every day,” Freckleton said. “I needed to rely on these people to guide my search.” She canceled a planned trip to a veterinary convention and spent hours with her textbooks. She created spreadsheets charting the dates each horse moved in and out of the farm, where and how they were kept, and how they were fed. Still, nothing seemed to add up. 

An important clue

In the meantime, Freckleton scrutinized the one horse who hadn’t become ill: Thunder, a Belgian draft horse. While his stablemates sank into depression and jaundice, Thunder remained happy and healthy. Freckleton started investigating every aspect of Thunder’s situation to see what made him different.

What she found was a broken stall door. Thunder had crashed through the door so many times in his impatience to be turned out that his daily routine had been adjusted. While the other horses stayed in their stalls after their grain meal and ate hay doled out from 80-pound bales, Thunder was turned out immediately after he finished his grain, which meant that he ate from the hay in his paddock, which came from a round bale.

Suddenly, the link between the sick horses was clear: It was the 80-pound hay bales. They had come from a nearby farm that had supplied Triple J and other stables in the area for years. A visual inspection turned up nothing unusual. “It looked like bland, boring grass hay,” says Freckleton. “It was a nice green color and smelled fabulous. No molds or toxins. I could not imagine how this hay would be the problem.”

As she studied the bales, however, Freckleton realized that she couldn’t identify one of the grasses in the mix. She saw a little fescue, a little crabgrass and a lot of something else. After poring over plant identification books, she determined that the mystery grass was fall panicum, a species native to Virginia that had no documented history of causing problems in livestock. A related species, however, had been implicated in equine liver disease in the Southwest.

Freckleton put in another call to Divers, who had mentioned the possibility of panicum poisoning in their first conversation. When she told him about the hay, he said he had heard of two other fall panicum-related outbreaks of equine liver diseae in Virginia and Maryland in recent years.

However, only testing would tell whether the same thing was happening at the Triple J. Twenty-five bales were loaded into a pickup and hauled to the Cornell campus in Ithaca, New York, eight hours away. Meanwhile, Divers prepared to start a study on fall panicum and equine liver disease.

Testing a Theory

Amy Johnson, DVM, a veterinary resident at Cornell, helped Divers with the study. The methodology was fairly simple: “To prove that hay was the cause of liver disease, we needed to feed it to horses we knew were healthy before they started eating it and were in a controlled environment,” she says. “They hay would be the only common factor between the research horses and the Virginia horses.”

At the start of the experiment, the researchers collected blood samples and liver tissue from two healthy study horses. They then fed them free-choice fall panicum hay from Triple J for 12 days. Over that time, they collected four more blood and tissue samples, and a botanist examined the hay, identifying five grass species—crabgrass, yellow nutsedge, barnyard grass, spotted spurge and, by far the most abundant, fall panicum.

By the end of the study period, the research horses not only became ill with signs similar to those seen in the Virginia herd, but blood and tissue analysis yielded the same diagnosis: liver failure. On horse’s condition deteriorated so much that he was euthanatized, but the surviving horse made a full recovery when he was returned to regular hay after the trial. “The liver has a pretty amazing capacity to regenerate, compared to other organs,” says Johnson, who eventually wrote a paper on the study for the Journal of Veterinary Internal Medicine.

A slow recovery

Back in Virginia, Freckleton was keeping a notebook to document the progress of each of the Triple J horses. She divided her patients into three groups: A (really sick), B (mildly sick with changes in bloodwork), and C (healthy to look at but with minor changes in bloodwork). Then there was Thunder, who was still in a category by himself.

In mid-December the first two horses to take sick after Ninety-Nine had to be euthanatized. On December 21 two more became severely ill and later died of complications related to liver disease. “Near Christmas, it was creepy to walk into the barn,” Freckleton says. ‘You’d see glassy-eyed horses, standing silent. No chewing, no fidgeting, no horses talking to each other or banging the door for treats. The horses didn’t care if you came or went.”

The remaining animals received steroids and antibiotics, and their blood was tested at least once a week. The expense mounted, and so did the work. Because Triple J was not staffed to stable horses 24 hours a day, the horses’ owner pitched in to help, cleaning stalls, feeding and watering.

About mid-January things started to turn around. In fact, Freckleton drew happy faces on her notes for January 14. Two weeks later, the liver values of the surviving horses were still not completely back to normal, but they were well enough to go off their medications. “From the end of January on, everyone was recovering and doing week,” she says.

Of 14 horses diagnosed with liver disease at Triple J, five were euthanatized. During the following spring there was some concern about how the survivors would handle vaccinations and deworming, but blood tests showed no problems.

Although life at Triple J has returned to normal, questions about the fall panicum poisoning linger. Most important, the researchers have not been able to determine how fall panicum causes liver disesase. They suspect that the plant’s saponin, a waxy protective coating, may contain a toxin, but this has yet to be proven.

Another oddity is the sporadic nature of fall panicum poisoning. All of the anecdotal reports seemed to suggest that toxicity is most likely to occur in late fall or early winter when horses are fed fall panicum hay harvested during the same year. Weather, time of harvest or variations in saponin concentration may all play a role. “We’re not sure exactly what makes it toxic,” Johson says. “We can’t predict, given a field of panicum, if it’s likely to happen again.”

The hay that cause the trouble at Triple J was donated to a landscaper and horses in the area were alerted to the potential danger. Many of the surrounding hay growers replanted their fields to eliminate the grass. The owners of Triple J, who lost two of her own horses, still buys hay from her original supplier but requests cuttings from a different field. She also always checks to make sure there is no panicum in the mix.

“This hay is not a problem every time you feed it,” Freckleton says. ‘But until we know how to identify which batch or conditions are dangerous, I recommend that my clients avoid it. It would be a good PhD project to figure out what condition makes this dangerous. I’d love to see other horses not have to go through this.”

This article first appeared in the June 2007 issue of EQUUS Magazine




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