Top Equine Medicine Studies of 2013

In one study Clark described, researchers tested metformin's effects on insulin responses, and believe the drug could be a useful pre-turnout approach to preventing insulin spikes in horses at risk for developing EMS or EMS-induced laminitis.


A must-attend session for many of the practitioners at the American Association of Equine Practitioners' annual convention is the Kester News Hour, which features a panel of expert practitioners who summarize recent research results from the areas of equine medicine, surgery, and reproduction. At the 2013 convention, held Dec. 7-11 in Nashville, Tenn., attendees welcomed Carol Clark, DVM, Dipl. ACVIM, of Peterson & Smith Equine Hospital, in Ocala, Fla., to the Kester panel for the first time, and listened as she offered concise equine medicine literature reviews.


Clark began by describing research surrounding equine eye conditions, highlighting a paper in which researchers reviewed the clinical signs, diagnostic methods, and treatment options for equine subepithelial keratomycosis, a fungal infection of the eye. They found that one-quarter of these cases have a “punctuate” appearance (with little specks dotting the eye), Clark reported, while half the cases have a more diffuse appearance. The remaining one-quarter of cases present with both features. The team also found that the best way to diagnose these cases is by obtaining a cellular sample for culture and evaluating the structure of the cultured fungus to identify it, she said. Another helpful diagnostic tool is horses’ response to antifungal treatment—Clark said nearly all the cases resolved within four to five weeks of using this approach. She remarked, “It is yet unknown if this is the beginning of an ulcerative fungal infection or its own disease entity.”

Next, Clark shared a study in which researchers evaluated the use of topical anesthetics for numbing the horse's eye for veterinary ophthalmic procedures. While proparicaine has always been the preferred ophthalmic anesthetic, the authors indicated that other topical choices are just as effective, such as lidocaine and bupivicaine. They determined that mepivicaine does not achieve complete anesthesia, Clark cautioned, but the other anesthetics' effects were usually apparent within a minute, with a maximum effect observed within five minutes of topical treatment.

Clark also touched on a study in which scientists examined eosinophilic keratitis in mid-Atlantic states. Researchers found that this invasion of the equine cornea with a type of white blood cell tends to be a summer syndrome, with 92% of cases occurring between June and October. Almost half of the cases evaluated were recurrent, with horses having been infected in previous years. The typical healing time for eosinophilic keratitis cases is about 3.7 months, Clark said, and topical corticosteroid treatment did not decrease healing time. On the contrary, systemic corticosteroids (such as dexamethasone) shortened healing time by 2.2 months, and cetirizine (an antihistamine) lessened the chance of recurrence.



Clark then moved to papers involving equine protozoal myeloencephalitis (EPM) diagnosis in the living horse. In one study, researchers determined that the most accurate means of detecting EPM is to use a simple titer ratio of antibodies in serum to those in cerebral spinal fluid (CSF). The team concluded that using this titer ratio offered excellent sensitivity and specificity for diagnosing EPM in the live horse, she said.

Clark also reported on a study in which researchers further examined the usefulness of serum testing, CSF testing, and serum to CSF titer ratios by comparing the results with neurologic deficits consistent with EPM and necropsy results on those cases. The authors similarly confirmed that serum testing very poorly correlates with post-mortem confirmation of disease, she said, and while CSF testing alone has been a standard test for a long time, the best diagnostic test to use appears to be the serum:CSF ratio titer. Clark stressed that evidence of antibody production within the CSF is important for diagnosing EPM and serum testing alone is not at all reliable.



Moving on, Clark described a paper in which authors compared the effects of oral vs. intravenous (IV) fluid therapy on whole body hydration. They concluded that both “maintenance” (the standard volume used to maintain a sick horse’s hydration to keep normal metabolism and organs functional) and double-maintenance dose IV fluids are effective volumes for restoring hydration in dehydrated horses. However, Clark said, the team found that a triple-maintenance dose of IV fluids did not improve horses’ hydration status and increased urine output; ultimately, horses receiving triple-maintenance doses of IV fluids were less hydrated than those receiving a maintenance or double dose once IV fluid therapy was stopped. Clark also mentioned that the researchers showed that oral fluid replacement—passing fluid through a nasogastric tube into the animal's stomach—is an excellent means of restoring intestinal water levels. In addition, she said, kidney fluid losses through urination are less likely when restoring intestinal water with oral administration.


Blister Beetle Toxicosis

It takes just three ingested blister beetles from hay or pasture to kill an adult horse, and in the next study Clark described researchers evaluated which treatments work best for treating so-called blister beetle toxicosis. They examined the effectiveness of three gastrointestinal therapies—mineral oil, charcoal, and smectite (or Biosponge)—in rats that had received cantharidin, the toxic substance found in blister beetles. They found that mineral oil was associated with the highest mortality rate: six of eight treated animals died. Three of eight rats died after receiving toxin and no treatment (the control group), Clark said, while two of eight rats died after treatment with charcoal or smectite. The bottom line: Mineral oil—or any lipid soluble—should not be used in suspect cases of blister beetle toxicity because it appears to exacerbate cantharidin absorption and increase mortality.


Long Distance Hauling and the Respiratory Tract

Horses that travel long distances are prone to developing respiratory infections, often due to damage to their respiratory tract epithelium caused by environmental factors within the trailer (such as hay or dust), stress, and holding the head in an elevated, fixed position. Clenbuterol is a medication designed to improve the tracheal lining's ability to transport inhaled debris out of the airway. Clark described a study in which authors evaluated if clenbuterol could provide relief to traveling horses. The research team administered clenbuterol 12 hours prior to transport and then every 12 hours over the next 48 hours and found it improved tracheal clearance of debris by at least 50%. The drug can reduce respiratory disease development following transport, she said, however it's important to keep in mind that drug testing on athletic horses means that veterinarians or owners using the drug must allow for appropriate withdrawal times.


Inflammatory Mediator Inhibitors

Matrix metalloproteinases (MMPs) are inflammatory mediators that play an important role in the development of equine conditions such as laminitis, recurrent airway disease, hepatitis, and osteoarthritis. Clark described the results from a study in which authors compared potential MMP inhibitors–specifically, doxycycline, oxytetracycline, flunixin meglumine, and pentoxyfylline–to suppress specific MMP components that cause inflammation. Clark said the team found pentoxyfylline to be the most useful MMP inhibitor used in the study with oxytetracycline coming in second. The results of this study can help veterinarians better understand the medications that best control inflammation caused by MMPs.


Equine Metabolic Syndrome

Researchers are getting closer to establishing one reliable treatment method for the hormonal disease equine metabolic syndrome (EMS). Clark shared on a study in which the authors tried to find ways to blunt abnormal insulin responses. Healthy horses (not EMS-affected) were given a large dose of dexamethasone to elicit insulin resistance. Then these horses were administered metformin (30 mg/kg) one hour prior to administering oral sugar. The team found that metformin reduced the horses' insulin response. Clark said the researchers believe metformin has a local intestinal effect on reducing sugar absorption and might be a useful pre-turnout approach to preventing insulin spikes in horses that are at risk for developing EMS or EMS-induced laminitis.


Effects of Equine vs. Canine Firocoxib

When prescribing the NSAID (non-steroidal anti-inflammatory drug) firocoxib for horses, some veterinarians have opted for using the canine pill version, Previcox, rather than the more expensive equine version of the same pharmaceutical agent, Equioxx paste. Researchers who completed the next study Clark described found that the canine tablet is just as effective as the equine paste. But she noted one major problem: It is illegal to use or for veterinarians to prescribe the canine version for use in the horse. The FDA claims that “cost is not a justification for using an off-label drug,” particularly when an equine formulation is available.

Clark stressed that use of the canine drug could remove owners’ ability to make equine insurance policy claims, and, when using the canine product in horses, accumulated drug levels could lead to positive drug tests. Veterianrians have determined withdrawal times for Equioxx, whereas this is not the case for Previcox. Previcox and Equioxx's manufacturer is working on developing another, less-expensive equine oral firocoxib form, Clark relayed. She also pointed out that three times the recommended dose of Equioxx may better serve as a loading dose to achieve maintenance levels more quickly.

  • Barton MH, Paske E, Norton N, et al. Efficacy of cyclo-oxygenase inhibition by two commercially available firocoxib products in horses. Equine Vet J early view 16 Jul 2013. 

Digital Cryotherapy:

The final studies Clark described were centered around digital cryotherapy—or, icing the hooves--to minimize laminitis risk. Researchers found that that 21% of horses with colitis (inflammation of the large colon) developed secondary laminitis. In this study, only 10% of horses treated with the ice slurry developed laminitis as compared to 33% of those not treated with the ice slurry. “Colitis horses treated with ice had 10 times less odds of developing laminitis compared with horses treated without ice,” the researchers reported.

Clark described one strategy to minimize horses’ risk of developing laminitis: standing the affected horses' front limbs in an ice slurry. Ice boots, ice packs, and ice gel do not have the same effect as the slurry. Used 5-liter intravenous fluid bags can also be filled with an ice slurry, then wrapped around the horse’s lower limb, she added. Additionally, digital cryotherapy can be an important technique for preventing laminitis in horses with serious systemic or intestinal illness, or Potomac horse fever, Clark said


About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her recent book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care (available at or by calling 800/582-5604). She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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