Red Maple Poisoning Survivor

When a pony ingests a deadly toxin, his unusually stoic nature helps him beat the odds.

Red maple leaves have three to five lobes, silver-white undersides and bright red stems. Photo © EQUUS

Something was clearly wrong with Feelin’ My Oats. The 5-year-old Connemara/Welsh pony, called “Oats,” usually expressed a cheerful interest in everything, especially eating. But on the morning of September 21, 2010, the 13-hand buckskin gelding failed to come in for his grain.

“He was just standing there, real lethargic,” says his owner, Candi Hylton. Her husband, Bernard, put a halter on the pony and walked him in to the barn. Oats’ depressed demeanor suggested that he might be colicking, but he didn’t appear to be in significant pain. A quick check of his temperature revealed it was slightly elevated at 102 degrees. At first Hylton was only a little concerned about the pony, but she became alarmed when Oats stretched out to urinate—and produced a stream of dark, almost coffee-colored, urine.

Thinking quickly, she grabbed a bucket to take a sample. Then she phoned Appalachian Veterinary Services in Christiansburg, Virginia, where she also happened to have worked in the front office years earlier. The on-call veterinarian headed out right away.

Hylton and her husband had been scheduled to deliver Oats and a few other horses from their boarding and training farm to a show at the county fairgrounds that morning. Leaving the sick pony under the watchful eye of the morning barn help, she and Bernard left to deliver the other horses. She would wait anxiously for a call to her cell phone with an update.

The veterinarian who arrived, a recent graduate, immediately knew Oats was in serious trouble. Dark brown or black urine is a sign that the body is excreting debris from damaged cells. Something inside Oats’ body was breaking down and had been for some time. The veterinarian called the office and consulted with the practice owner, Kent Adams, DVM.

“I could tell it was serious from the sound of that first call,” Adams says. The veterinary team still wasn’t sure exactly what they were dealing with: In addition to the dark urine and fever, Oats was lethargic, his heart and respiratory rates were elevated, and his gums were a slightly “muddy” color, indicating that his cells might not be getting enough oxygen.

The veterinarian gave Oats a dose of Banamine to help control any pain he might be experiencing and “tubed” him because of his decreased gut sounds, scant feces on rectal palpation and loss of appetite. The hope was to address any gastrointestinal problems while he considered the diagnostic possibilities for the unusual set of clinical signs. To gather more clues, he pulled a blood sample and headed back to the office to analyze it.

The results of the blood test shocked everyone: Oats had a hematocrit (HCT) of only 14 percent. HCT is a measure of the percentage of red blood cells in the blood; the normal value is 31 to 53. A level of 14 percent is very serious and potentially life-threatening. The pony had so few red blood cells circulating in his bloodstream that his vital organs, and indeed all of his tissues, were slowly being starved of oxygen. The dark urine indicated that red blood cells, and possibly other tissues, were being destroyed inside his body. These signs, combined with Oats’ muddy gums and depressed behavior, plus a careful survey of his turnout paddock, all pointed toward one very serious diagnosis: red maple toxicosis.

Deadly leaves
Red maple toxicosis (poisoning) occurs when horses eat wilted leaves from Acer rubrum trees. Red maples, also called swamp maples or soft maples, are medium-sized trees with distinctly shaped three- to five-lobed green leaves with jagged edges, V-shaped notches between the lobes, bright red stems and silver-white undersides. The trees are native to the eastern United States, but they are planted all over the country. The leaves contain several toxins, most notably gallic acid, that can lead to the destruction of red blood cells (hemolysis). A horse who nibbles on a few fresh green leaves, which are mostly water, isn’t likely to get a toxic dose. But one to three pounds can be a fatal dose for an average adult horse, and half a pound can kill a small pony. As the moisture content of the leaves decreases, the levels of the toxic principle increases: It is generally thought that lush spring growth is less toxic than later summer or early fall leaves.

“It’s a common misconception that [red maple poisoning] happens most frequently in the mid- to late autumn, when leaves turn colors and fall from the trees,” says Adams. “But in reality, in late summer when pastures are short, downed branches are much more of a threat because of both the quantity and appeal of the green leaves. In fact, the majority of cases I see are in late summer following a thunderstorm, when a branch falls and the pastures are sparse. Horses go looking for something to chew on and find those leaves.”

The exact source of the toxicity in red maple leaves has not yet been pinned down, but the effects within the body are well documented: “The toxin attaches to hemoglobin in the red blood cells, rendering them incapable of transporting oxygen,” explains Adams. “Some of the cells rupture, releasing hemoglobin into the bloodstream. That stresses the kidneys by clogging up the blood-filtration system. Meanwhile, the liver and spleen are identifying nonfunctioning cells with damaged hemoglobin and removing them from circulation faster than they can be replaced by the bone marrow. The end result is a horse who is essentially suffocating, with extensive damage to vessel-rich organs that depend on oxygen, like the heart, lungs, brain and kidneys.”

Starved of oxygen, the organs begin to shut down, usually about 72 hours after the horse eats as little as a handful of leaves. Severe colic and laminitis from circulatory dysfunction are common complications. “The spleen can release its stores of red blood cells, but that’s only about 10 percent of the total volume, and those cells will quickly die or be destroyed just like the others,” says Adams.

There is no specific antidote or effective treatment for red maple poisoning, but supportive care, including intravenous fluids and possibly blood transfusions, may help a horse survive. Infusions of vitamin C may also help, if the problem is caught in its earliest stages. “So it comes down to, ‘Can the horse live long enough—can his kidneys and other organs remain functioning long enough—for the toxin to be used up and new blood to not be affected,'” says Adams. “Most of the time, the answer is ‘No, he can’t.'” About 70 percent of horses with red maple toxicity do not survive.

Adams relayed the grim diagnosis to Hylton, who immediately headed home from the fairgrounds, hoping Oats would still be alive when she got there. He was.

Although Oats displayed all of the classic signs of advanced red maple poisoning—and his HCT indicated that he’d eaten at least a couple of pounds of the leaves a day or more before his problem was discovered—his case was distinctly unusual in one way: “In the early stages, even before we see red urine from the hemolysis, the gut slows down, experiences marked irritation and colic sets in. It’s usually a fairly painful process,” says Adams. “So, by the time we identify what’s going on through blood work, the horse is usually in significant pain or refusing to stand.”

Oats was by no means perky, but he was still standing, drinking some and even eating small amounts of hay. Also, his gums were only slightly off in color, not the deep brownish hue that can be more typical of the condition. Taken together, these signs suggested that he was in the early stages of toxicity or he had gotten only a relatively small dose of the toxin, contrary to his blood work.

“What was remarkable is that he wasn’t panicking and severely stressed,” says Adams. “He was clearly in some discomfort and in distress, but he was staying on his feet. He would start breathing heavily if he moved much, but if you let him stand there, he seemed to be coping very well.” This stoic nature was serving Oats well—when a horse with red maple toxicosis gets agitated and thrashes, he uses up his limited oxygen supplies that much faster and can make the situation worse.

Tough decisions
The Hyltons’ first course of action that day was to find the source of the red maple leaves Oats had eaten to protect the rest of their horses. Although the pony had been in a large pasture that morning, he’d spent the previous day in a sparse “diet” turnout area. “The maple tree was over the diet pen,” says Hylton. “And we’d had a rainstorm. Bernard found a small limb that had fallen off, and you could see where leaves were gone off of it. When Oats is in the diet pen he will literally eat anything that has a leaf.” Bernard removed the limb and searched the property for any others that may have come down.

Meanwhile, Hylton had a long discussion with Adams about treatment options. “The first thing you think of is transporting the horse to a clinic where you can do a blood transfusion,” says Adams. “But given how low his oxygen levels were, the stress of such a trip could very well have killed him.”

Adams also had doubts about the benefits a transfusion might ultimately have for the pony: “Blood transfusions in horses have limited utility because they have so many blood types—you can’t get an exact match. Plus, in cases of red maple poisoning, any blood you do put in is going to be destroyed by the same processes as long as the toxin is circulating. So you get maybe 24 hours of benefit.”

All in all, it seemed better to leave Oats where he was and keep stress to an absolute minimum. His blood results had shown that his kidneys, liver and other vital organs were still functioning, and if he didn’t move around much his respiratory rate was nearly normal. “He was a very sick horse—no doubt about it—but his body seemed to be handling the situation remarkably well at that point,” says Adams. “He seemed to be holding his own.”

The veterinarian was also reluctant to try giving Oats intravenous fluids for fear it could upset the pony’s fragile physiological balance. “You can expand their blood volume with intravenous fluid, which will lower the total [HCT] levels even further,” says Adams. “There’s always the urge to do something, but sometimes you need to step back and make sure what you do doesn’t create a bigger problem.”

After discussing all of these factors, Adams and Hylton arrived at what may seem like a startling treatment plan: They would try to control Oat’s pain and discomfort and not much else—at least for the moment. “This wasn’t a case of ‘Oh, it’s just a pony, let’s wait and see what happens,'” says Adams. “And it wasn’t a case of an owner deciding things weren’t bad enough yet to call a veterinarian. Far from it. There was intense discussion to understand all the nuances and risks before making some very difficult decisions.” Confident that Oats was comfortable and as stable as possible, Hylton remained close by to monitor the pony’s condition.

Hanging on, day by day
Oats’ condition was unchanged the next day. He remained lethargic and slightly feverish with brown urine, all indications that his blood was still under assault from the toxin. And yet he remained on his feet, eating and drinking normally. Hylton watched him nearly continuously for signs of colic or laminitis, but the pony seemed to be holding his own.

A veterinarian from the practice returned to check on Oats that morning, and on the third day, Adams himself came back out to the farm to draw another blood sample to check the gelding’s HCT level. An increase in the number would be a sign that he had turned a corner and that his blood was no longer being destroyed by the toxin or removed by the liver and spleen.

Using a portable unit to run the blood test on site, Adams had results in minutes—and they were shocking. Oats’ HCT had dropped even further, to an astonishing 9 percent. According to the textbooks, a horse with an HCT that low should be in severe distress—or dead. Yet, there stood Oats, very much alive.

Hylton and Adams had another long conversation. The risks associated with transport, transfusions or intravenous fluids were still present, perhaps even greater. And although Oats was undoubtedly getting sicker, he still didn’t seem to “need” the supportive treatments. He showed no outward signs that his condition had worsened. In fact, his urine appeared lighter in color that day, a sign that the destruction of his blood cells was diminishing.

“We decided to let things be,” Hylton says. Oats remained in his stall, kept as quiet as possible while his owner monitored his care: “I was taking his temperature and listening to his gut and heart and giving [the veterinarians] a call several times a day to let them know how he was.”

Receiving these regular reports helped support Adams’ decision to not intervene medically: “Candi is an incredibly knowledgeable and diligent horsewoman. I knew she’d notice any changes and report it immediately.”

But the day after his astonishingly low HCT, Oats began to perk up. He moved around in his stall, and his temperature and heart rate started to come down. After another day, Hylton took him for a short hand-walk outside his stall. He pulled her toward the grass and ate voraciously.

Seven days after the initial veterinary visit, Oats was rechecked and a third blood test performed. This time, the pony’s HCT was 31 percent, edging into the normal range. His liver and kidney functions were normal, and he showed no clinical signs of colic or laminitis. Oats’ body, it seemed, had powered through the worst of red maple toxicity and was well on the road to recovery.

“It’s really a remarkable case,” says Adams. “I wouldn’t have believed the recovery in light of the dramatic lab findings if I hadn’t seen it myself.”

A few weeks later Oats was turned out with the herd again, and several months later Hylton began riding him cautiously. Finally, one year after the day he was found in the field so lethargic and weak, the pony made the trip to the county fair. He has never shown any adverse effects from his ordeal.

Adams uses Oats’ story as a teaching tool in continuing-education seminars for veterinarians. “This case really highlights the complex issues you face when treating red maple poisoning and how understanding the pathology is crucial so you don’t inadvertently make the situation worse; in some cases intravenous fluids or whole blood transfusion might make things worse,” he says. “Plus, it’s nice to be able to present a case with such a good outcome. He really is a remarkable pony.”

This article first appeared in EQUUS issue #425.




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