Around the globe veterinary scientists investigate equine health issues in a search of new treatments and diagnostics or to substantiate conventional wisdom.

Each year during the Kester News Hour, part of the annual American Association of Equine Practitioners Convention, three esteemed veterinarians offer their top picks from current published studies in their respective specialty areas of surgery, reproduction, or medicine in a popcorn-style research roundup.

At the 2016 meeting, held Dec. 3-7 in Orlando, Florida, Rob MacKay, BVSc, PhD, Dipl. ACVIM, a professor at the University of Florida, in Gainesville, presented his selection of research topics in medicine, ranging from equine herpesvirus to headshaking.

Heparin for EHM Prevention

Equine herpesvirus myeloencephalopathy (EHM) is the dreaded neurologic form of equine herpesvirus-1 (EHV-1). During outbreaks, infection control and treatment are paramount, but the virus still confounds veterinarians for one reason: No reliable and tested medication is available for treating or preventing the disease.

Enter a research team from the University of Zurich, in Switzerland, and an EHV-1 outbreak that involved 61 horses. The veterinarians hypothesized that the drug heparin, a blood thinner/anticoagulant, might help manage EHM infection spread during outbreaks because of the virus’ procoagulant nature. So, beginning on Day 10 of the outbreak, the team administered heparin to 31 EHV-1-infected horses on the first day of fever, before the onset of neurologic signs. Thirty horses infected with EHV-1 before Day 10 of the outbreak were not given heparin.

The researchers analyzed results after the outbreak and found that the heparin-treated horses showed a lower EHM incidence (one out of 31) than did the untreated horses (7 out of 30). Results indicate that heparin might be useful in managing EHM spread during an outbreak, MacKay said, but because important controls were not possible during this study, the work needs to be confirmed by additional studies.

Walter J, Seeh C, Fey K, et al. Prevention of equine herpesvirus myeloencephalopathy – Is heparin a novel option? Tierärztl Prax 2016;44:313-317.

Diet and Omeprazole to Control Equine Gastric Ulcers

Veterinarians who treat horses with equine gastric ulcer syndrome (EGUS)—and owners who manage them—know that keeping EGUS under control is a balance between medication, feed type, and feeding schedule. In an effort to provide “real world” data on the efficacy of omeprazole for suppressing gastric acidity in the horse (which is related to the formation and recurrence of EGUS), Australian and British investigators took a closer look at diet and drug treatment for affected horses.

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In the study, a group of horses consumed two different diets, one a free-fed (at liberty) “all-hay diet” and the other a concentrate-based (high-grain, low-fiber diet) “racehorse diet.” MacKay noted that veterinarians often recommend high-forage, low-concentrate diets to manage EGUS by simulating the horse’s natural grazing tendencies. Conventional wisdom for treating EGUS would say that horses on an all-hay diet would do better than horses on a concentrated, grain-based feed.

In addition to the two diets, the study horses also received omeprazole treatment.

Researchers then measured the horses’ stomach pH on Day 0 for a baseline and recorded their stomach pH for continuous 23-hour cycles. Ideally, EGUS treatment with omeprazole raises stomach pH (making it less acidic), allowing existing ulcers to heal.

The seemingly surprising study result? The “racehorse diet” group fared better, with their stomach pH improving the most after omeprazole administration, MacKay said.

But don’t throw out your slow-feeders just yet. Rather, MacKay said, the study simply suggests omeprazole works best when administered on an empty stomach, and veterinarians should consider making minor feeding schedule adjustments to accommodate drug treatment times. “Withhold hay for two hours before and after dosing,” Mackay suggested.

Sykes BW, Underwood C, Greer R, et al. The effects of dose and diet on the pharmacodynamics of omeprazole in the horse. Equine Vet J 2016; DOI: 10.1111/evj.12630.

Liver Failure Related to Supplement

An otherwise healthy 8-year-old Holsteiner gelding presented to the University of Pennsylvania School of Veterinary Medicine’s (Penn Vet) New Bolton Center, in Kennett Square, colicky, off his feed, listless, and jaundiced. Ultimately veterinarians euthanized the horse, but subsequently found that he had a small, flaccid liver and Alzheimer-like cells in his brain.

All signs pointed to liver failure and consequent brain disease related to toxicity. But what caused the horse’s acute illness? No other horses in his barn showed signs of sickness, and veterinarians found no evidence of hay or feed contamination or potential exposure to toxic plants. The research team started sleuthing to uncover the cause, ultimately testing an oral supplement containing C-phycocyanin that the horse’s owner had purchased to support his joint health.

C-phycocyanin is derived from blue-green algae (cyanobacteria), and research shows it might have anti-inflammatory and antioxidative properties that help osteoarthritis is horses, dogs, and humans. However, blue-green algae can also produce microcystins, which are highly toxic and often associated with algal blooms.

In this case, tests confirmed that three containers of the supplement purchased for the horse—including one that was open and had been fed to him—contained the toxins. The veterinarians concluded that consuming the toxic supplement had likely sickened the horse, leading to his death.

MacKay’s takeaway: Despite professional-looking label and marketing claims “supplements are not always safe,” he said. Furthermore, he pointed out that blue-green algae harvesting and processing for supplements is not regulated.

Mittelman NS, Engiles JB, Murphy L, et al. Presumptive iatrogenic microcystin-associated liver failure and encephalopathy in a Holsteiner gelding. J Vet Intern Med 2016;30:1747-1751.

Effect of Rifampin on Clarithromycin Absorption in Foals

Veterinarians commonly use the antibiotic rifampin in combination with a macrolide antibiotic such as clarithromycin to treat Rhodococcus equi infections in foals. A team of German researchers compared the pharmacokinetics (how drugs move through the body) of clarithromycin (CLA) given orally with rifampin to data from foals given CLA alone. They found that CLA concentrations lowered by more than 80% in foals’ blood and bronchoalveolar cells when rifampin was co-administered with CLA.

Although CLA absorption was improved by giving the rifampin four hours after CLA, rather than at the same time, this effect was slight, and the investigators did not consider it clinically significant.

The research team found that rifampin suppressed CLA absorption by upregulating the actions of P-glycoprotein, an “efflux protein” that actively pumps the antibiotic back into the gut’s lumen.

For MacKay, the study’s main take-home is that rifampin likely severely reduces uptake of all macrolides used for R. equi treatment (i.e., CLA, azithromycin, erythromycin). Notwithstanding this effect, the CLA/rifampin combination remains a clinically effective R. equi treatment.

“More work is needed to discern whether the perceived advantage of rifampin outweighs the negative effects on macrolide absorption,” MacKay said.

Berlin S, Spieckermann L, Oswald S, et al. Pharmacokinetics and pulmonary distribution of clarithromycin and rifampicin after concomitant and consecutive administration in foals. Mol Pharm 2016;13:1089-1099.

Retrospective Look at Lyme Neuroborreliosis

The neurologic form of Lyme disease in horses—or more accurately, equine neuroborreliosis (NB)—is as difficult to describe as it is to diagnose, in part because little literature on the subject exists. That’s why a research group at Penn Vet delved into a retrospective study of equine NB cases in hope of providing a detailed description of the disease’s clinical signs, diagnostics, and pathologic findings.

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Sixteen equine cases qualified for the research paper based on basic selection criteria, which included location in areas of the northeastern United States known to be at high risk for Lyme disease and post-mortem histologic findings consistent with previous reports of NB without evidence of other disease. Study candidates came from New Bolton’s own caseload, as well as other referral clinics in the northeast.

The study found variable clinical signs, including:

  • Muscle atrophy/weight loss;
  • Cranial nerve deficits;
  • Incoordination;
  • Changes in behavior;
  • Difficulty eating or swallowing;
  • Muscle tremors;
  • Neck stiffness;
  • Episodic respiratory distress;
  • Uveitis;
  • Fever;
  • Joint swelling; and
  • Heart irregularities.

Of the 16 horses, only six tested positive for Borrelia burgdorferi (the causative agent of Lyme disease) infection via standard immunodiagnostic testing of blood or cerebrospinal fluid. PCR testing on cerebrospinal fluid for exposure to the tick was negative in all seven cases that were tested.

MacKay’s takeaway: There’s still a lot we don’t know about Lyme disease in horses.

“Signs are nonspecific and numerous, routine bloodwork is unhelpful, and tests such as the Lyme multiplex are not diagnostic,” MacKay said.

Johnstone LK, Engiles JB, Aceto H, et al. Retrospective evaluation of horses diagnosed with neuroborreliosis on postmortem examination: 16 Cases (2004–2015). J Vet Intern Med 2016;30:1305–1312.

PENS for Treating Horse Headshaking

Headshaking in horses is a frustrating chronic problem—likely a response to nerve pain—that has no consistent, effective treatment. Managing cases can, in turn, leave veterinarians and horse owners shaking their own heads.

But there’s a promising new treatment that’s recently been tested by researchers from the University of Bristol, in Somerset, U.K.: percutaneous electrical nerve stimulation (PENS) therapy. This is a minimally invasive neuromodulatory (the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons) treatment used to manage human neuropathic pain.

Researchers looked at seven horses diagnosed with headshaking that showed clinical signs at the study’s onset. They sedated and treated the horses with a PENS probe following a protocol developed for managing nerve pain in people. The horses each received a series of three or four treatments, with researchers repeating treatments as headshaking signs recurred.

The results had MacKay shaking his head yes, calling the treatment protocol both “safe and promising.” All horses tolerated the treatments well, according to the paper. Two of the horses had increased headshaking for up to three days after the initial treatment session. Six of the study’s horses responded positively to their first treatment and returned to ridden work at the same level as prior to onset of headshaking. Five of the seven horses continuing to respond to subsequent treatments, gaining up to 20 weeks of relief from headshaking after the fourth treatment.

Roberts VLH, Patel NK, Tremaine WH. Neuromodulation using percutaneous electrical nerve stimulation for the management of trigeminal-mediated headshaking: A safe procedure resulting in medium-term remission in five of seven horses. Equine Vet J 2016;48:201-204.