Veterinary internists met June 6-9 in Seattle, Wash., for the 25th Forum of the American College of Veterinary Internal Medicine (ACVIM) to discuss the latest research on the internal workings of horses and other animals.

Summarized below are some of the highlights for horse owners:

Pain Management in Horses

Debra Sellon, DVM, PhD, Dipl. ACVIM, professor of Equine Medicine at Washington State University in Pullman, Wash., discussed some of the agents besides non-steroidal anti- inflammatory drugs (NSAIDs) used to control pain in horses. According to Sellon, an understanding of and familiarity with drugs of other classes can aid veterinarians in providing safer and more effective pain control in horses with either transient or chronic conditions.

In addition to the NSAIDs, opioids (such as butorphanol), ketamine, alpha-2 agonists (like xylazine and detomidine), local anesthetic drugs (such as lidocaine), and gabapentin can be used to manage different types of pain. Each class of drug has associated adverse effects and specific methods of administration that influence veterinarians’ choices in a given situation.

For instance, ketamine is most frequently used as a general anesthetic for horses undergoing surgery, but when administered continuously at a low dose, it confers pain-controlling and even anti-inflammatory effects that veterinarians can use to benefit certain patients.

Veterinarians who understand alternative applications of drugs can prescribe safer pain- controlling regimens for horses in their care. Combining medications from several different drug classes, or giving drugs via different routes, can keep veterinarians from having to rely on high doses of NSAID drugs that can lead to consequences such as kidney and gastrointestinal injury.

Equine Herpesvirus

A round table discussion about equine herpesvirus (EHV) was a popular equine session. EHV is a concern among many horse owners, considering the recent outbreaks at sport horse facilities such as Monmouth Park Racetrack and West Palm Beach show grounds. Typically, EHV causes abortion in pregnant mares and mild signs of respiratory disease and fevers in other horses, but the disease can occasionally cause severe neurologic deficits such as ataxia (incoordination) or recumbency (inability to get up). Veterinarians participating in the session discussed how the recent outbreaks could indicate that the virus has mutated and a new strain has emerged.

Acyclovir has been considered the drug of choice for treating horses with herpesvirus, but recent research on valacyclovir presented by Bradford Bentz, VMD, MS, Dipl. ACVIM, Dipl. ABVP, of Hagyard Equine Medical Institute of Lexington, Ky., shows promise. Valacyclovir, which is converted to acyclovir in the body, might achieve better blood levels of the active drug and be more effective against herpesvirus (see www.TheHorse.com/emag.aspx?id=8961).  

The ACVIM is drafting a consensus statement based on the round table discussion regarding the best methods for treating affected horses and managing outbreaks of EHV.

Pathophysiology of Laminitis

As always, discussions on laminitis are of keen interest to veterinarians who take care of horses. Jim Belknap, DVM, PhD, of The Ohio State University, summarized how scientific thinking about this devastating disorder has undergone a paradigm shift in the recent past.

Whereas it was once thought that impaired blood perfusion and hypoxia in the horse’s digit were the primary pathway leading to laminar inflammation, it is now understood that such a process alone does not explain the complex events that take place at the cellular level in the early stages of laminitis, before signs of lameness are apparent. Belknap and other laminitis researchers describe laminitis as a manifestation of organ damage that develops secondary to acute inflammation and report that laminar damage, while certainly exacerbated by oxygen deprivation, can proceed even when blood flow and oxygen delivery are adequate.

The damage that develops in the digit probably represents the sum effects of inflammation and blood flow alterations, with the latter aggravating and worsening the insult initiated by the inflammatory events.

This information has implications for horse owners, because measures can be taken to decrease the severity of the developing inflammatory state immediately after a horse has been exposed to a known laminitis trigger, such as grain overload or development of an inflammatory bowel disease like colitis.

Seasonal Variation in Incidence of Pasture-Associated Laminitis

Ray Geor, BVSc, MVSc, PhD, Dipl. ACVIM, professor and Paul Mellon Distinguished Chair at Middleburg Agricultural Research and Extension Center, Virginia Polytechnic and State University, spoke on pasture-related laminitis and reviewed what is known about the relationship between pasture carbohydrate content and insulin resistance in horses.

Obese horses or those that have what is called regional adiposity, most commonly recognized as crestiness of the neck, were more frequently affected with insulin resistance and were at higher risk for development of laminitis. Geor said that veterinarians see seasonal variation in the incidence of pasture-associated laminitis because there is seasonal variation in the nonstructural-carbohydrate content of pasture grasses, with concentrations highest in the spring, intermediate in the autumn, and lowest in mid-winter and summer.

Lawsonia intracellularis

Lawsonia intracellularis was once considered a disease of pigs, but in the last 10 years the disease has become a significant problem in horses, said Michele Frazer, DVM, Dipl. ACVIM, of Hagyard Equine Medical Institute in Lexington, Ky.

L. intracellularis is a bacterium that affects the gastrointestinal tract in young horses and results in low blood protein concentrations. Affected horses are typically less than one year of age and signs of illness are first noticed in the fall or early winter. The most common clinical sign is edema (fluid swelling) along the ventral aspect of the abdomen or in the lower limbs, but affected horses might also have diarrhea, lethargy, fevers, rough hair coat, or, less commonly, colic.

Frazer pointed out that horses respond well to treatment with several different antimicrobials. Severely affected horses might require treatment with plasma transfusions to replace the lost protein.–Kim Sprayberry, DVM, Dipl. ACVIM, and Michele Frazer, DVM, Dipl