The Otherwise Apparently Healthy Collapsing Horse
Stray voltage. Sleep terrors. Melatonin. Medical marijuana. These ingredients made up a lively lunchtime table topic veterinary discussion about horse collapse—a condition with primary causes ranging from sleep deprivation and pain to muscle disorders and pregnancy.

Key to treating a collapsing horse successfully is pinpointing the cause, which can take some sleuthing.

Joe Bertone, DVM, MS, Dipl. ACVS, and Stephen Reed, DVM, Dipl. ACVIM, described their approaches to these cases while moderating the discussion at the 2016 American Association of Equine Practitioners Convention, held in December in Orlando, Florida. Bertone is a professor of equine medicine at Western University of Health Science’s College of Veterinary Medicine, in Pomona, California, and has a special interest in sleep deprivation. Reed is an internist and shareholder at Rood & Riddle Equine Hospital, and his bailiwick is equine neurology; this means he sees a steady caseload of what he sometimes calls “clumsy horses,” or uncoordinated animals because of neurologic disorders. Both veterinarians possess an infectious enthusiasm for difficult-to-diagnose cases.

When Bertone gets a call about a collapsing horse, 90% of the time the horse is sleep-deprived. The other 10% of the time the horse is suffering solely from a neurologic, musculoskeletal, or other type of condition. Common reasons Bertone sees for horses collapsing that could fit in the sleep-deprivation category include boredom (think of a show horse collapsing in the crossties at 4 a.m. while being braided), dominance displacement (when an aggressive gelding keeps vigil and, thus, never sleeps), and the pain and pregnancy mentioned earlier.

Horses need paradoxical, or deep, sleep (aka rapid eye movement, or REM sleep) just like we do, said Bertone. They need to lie down to get this sleep, and can only go about two weeks without it before the body begins responding, sometimes in odd ways.

Veterinarians in the room regaled the group with stories about collapsing sleep-deprived horses they’ve treated, many of which were anxious for some known or unknown reason. Some examples included:

  • A mare that never lay down to sleep though would occasionally roll. She’d collapse intermittently, startling herself, and jump back to her feet. She could be ridden and worked because she was not neurologic. Fifty percent of the time the mare appeared either nervous or exhausted, said her veterinarian.
  • Another mare that collapsed regularly and was extremely anxious about everyday happenings, such as a palm frond falling to the ground near her stall. (Bertone said that 87% of his sleep deprivation cases are geldings—there just happened to be more mares described here.)
  • A group of horses that were chronically sleep-deprived, collapsing, and unwell that improved when the owner moved them away from buzzing overhead powerlines.
  • A horse that was treated for Lyme disease and finally lay down and got some sleep.
  • Horses that have “sleep terrors,” which prevent the horse from going into that restful period of paradoxical sleep. These horses paddle and kick and, just as humans, often do so with their eyes wide open.

Other types of cases described included muscle diseases (myopathies) in which horses have trouble getting to their feet because of muscle tissue pain, so they never lie down to get the deep paradoxical sleep that they need. Among these were mules suffering from hyperkalemic periodic paralysis (HYPP), which veterinarians said often leaves them recumbent (unable to rise) and unrecoverable.

Working Up Falling Down

When Reed works up a collapsing-horse case, and pain has already been ruled out, he checks the horse’s heart first, listening for atrial fibrillation or other types of conduction disturbances. Next, he conducts a neurologic exam, looking for a variety of signs that could predispose a horse to losing balance and falling, or that would cause the horse enough pain that it would avoid lying down.

Then he considers the horse’s metabolism. “Think of endocrinologic problems,” he said. “If they’re 17 and they haven’t developed PPID, then they certainly have that potential. When these conditions are suspected, further testing to rule out PPID or hypothyroidism is indicated.

“A physical exam, neurologic exam, along with some routine blood panels for complete blood count and master panel looking for underlying gastrointestinal, hepatic, or renal disease (can provide some insight) as well as giving an indication of whether inflammation or infection are present,” Reed said. “Beyond this, in search of more specific endocrinologic disorders, I would look for abnormal levels of blood glucose and insulin levels in blood.

“Horses that have PPID but fail to respond to treatment require reassessment of the clinical signs and consideration of additional diagnostic testing,” he added. Many of the horses Reed assesses typically suffer from spinal trauma, acute onset equine protozoal myeloencephalitis (EPM), or cervical stenotic myelopathy (CVM, or wobbler syndrome).

Bertone asks owners to set up 24/7 video for cases so he can watch for night terrors or simply look for signs of pain or behaviors that would prevent paradoxical sleep.

Amy Johnson, DVM, Dipl. ACVIM, of the University of Pennsylvania’s School of Veterinary Medicine at New Bolton Center, chimed in, saying she and her colleagues have found it valuable to work up these horses that collapse using video. Sue McDonnell, PhD, a certified applied animal behaviorist and the founding head of the equine behavior program at the school reviews the footage.

“The really invaluable thing is Dr. McDonnell’s differentiating the horses that are sleep deprived,” said Johnson. “She picks up a lot of pain behaviors that we miss as clinicians. They hide their discomfort from us.”

Added Bertone, “About half the time we cannot find a diagnosis. Once I’ve ruled out pain, made sure there’s no Lyme or sleep terrors, then I try different drugs.”

Let’s Talk Treatment

Reed said he prescribes two products for anxiety to help horses relax and sleep: Dilantin (phenytoin, an anticonvulsant, which also has some sedative properties) and Zylkene, a supplement that contains alpha-casozepine, a protein found in mare’s milk that promotes relaxation in patients that are anxious and stall-walking, particularly after surgical repairs.

For sleep terror cases, Bertone uses melatonin or changes up the horse’s environment, moving the horse to another part of the barn or adding a pony or other companion. Noting that research showed some children with sleep terrors were hypoglycemic, he suggested feeding affected horses later at night to see if that makes any difference.

Bertone also administers melatonin to anxious, sleep-deprived horses and said he’s surprised at how well it works. Still another option he prescribes is Prozac (fluoxetine), which he said can work, but takes about a month to become effective.

“But what about medical marijuana?” asked one veterinarian in attendance.

“It can work, in a state where it’s legal,” said Bertone, when other approaches haven’t worked, and when the practitioner has working knowledge of dosing in the species or can consult a veterinarian who does.

All Ears with an Eagle Eye

For some of the more unusual causes of collapse, treatment can be a process of elimination after a complete workup, involving a walk around the barn, looking for and listening for potential causes. For example, one horse that began collapsing did so after moving into a new barn. The veterinarian noticed a tree branch was rhythmically scratching the roof as the wind blew. The owners moved the horse away from the repetitive noise and the collapsing behavior stopped. At another farm a horse began collapsing after the farm owners changed the voltage of the barn’s lightbulbs; there was something about their sound that bothered the horses.

Finally, simply looking at your barn with a critical eye for safety can reveal a collapsing horse’s trigger. A veterinarian described a gelding that appeared healthy in his stall, but would knuckle over and collapse as soon as the owner would lead the horse into the aisle. None of the other horses behaved this way … but all the other horses were barefoot and this horse was shod. Ultimately, the veterinarian noticed an old extension cord lying nearby in a damp aisle—stray voltage was the culprit.

A new extension cord, stowed neatly away from the damp, was the cure.