The Horse

MAR 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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YOUR GUIDE TO THE 2018 AAEP CONVENTION A32 March 2019 The Horse | AAEP Wrap-Up Belgian Horse Owners: Test for SCC Squamous cell carcinoma (SCC) is the most common ocular cancer in horses. Belgians appear to be at a higher risk of developing SCC than some other breeds. Kelly Knickelbein, VMD, an ophthal- mology resident at the UC Davis Veteri- nary Medical Teaching Hospital, recently confirmed a genetic link between ocular SCC and Belgians. Squamous cell carcinoma tumors around the eye most commonly affect Haflingers and Belgians but are also reported in Clydesdales and other draft breeds, Quarter Horses, Appaloosas, Thoroughbreds, and more. Knickelbein said chestnut horses appear to be at higher risk of developing ocular SCC than horses with other coat colors, presumably because their coats lack a photoprotective pigment that prevents DNA damage as- sociated with ultraviolet (UV) exposure. In a recent study of Haflingers, UC Davis researchers identified a genetic risk factor for ocular SCC within that breed. It occurs in a variant of a gene called DDB2, which codes for a protein involved in DNA repair following UV damage. They found that nearly 80% of affected Haflingers were homozygous (had two copies) for the DDB2 genetic variant. So Knickelbein and colleagues investigated whether having the DDB2 variant or a chestnut coat were risk factors for ocular SCC in Belgians. Knickelbein said the results show that Belgians have the same genetic risk factor for SCC as do Haflingers. Belgian horses homozygous for the DDB2 variant are four times more likely to develop ocular SCC than those that are not homozygous. They found no significant association with coat color. Knickelbein recommended that owners of Belgians have their horses genetically tested (a test is available at the UC Davis Veterinary Genetics Laboratory) and use the results to guide breeding and manage- ment decisions. She advised stabling horses during peak sunlight hours and outfitting them with UV-protective fly masks to help reduce SCC risk. She also urged owners of high-risk horses to have their vets perform frequent eye exams. h Vets Discuss How to Use SAA in Practice Does your practice routinely use serum amyloid A (SAA) testing and, if so, how? Are you looking to implement this test into your toolbox but aren't sure how to go about it? Two internal medicine veterinarians answered these questions during a Table Topic discussion. Nicola Pusterla, DVM, PhD, Dipl. ACVIM, professor of medicine and epidemiology at the University of California, Davis, School of Veterinary Medicine, and Laura H. Javsicas, VMD, Dipl. ACVIM, from Rhinebeck Equine LLP, in New York, co-mediated the session. They kicked it off with a brief review of SAA basics. Pusterla reminded attendees that SAA—an acute-phase protein produced by the liver—essentially acts as a marker of inflammation. He highlighted the fact that while SAA is a powerful indicator that inflam- mation is present, the test can't tell you what's causing the inflamma- tion or, importantly, where it is. "Infection, trauma, neoplasia (tumors), and more can all cause inflammation," Pusterla said. "Together with a complete physical examination and other routine diagnostic blood tests, SAA can provide powerful real-time information about whether treatment/intervention is required, whether the inflammation is improving or getting worse during treatment, and even when treatment should be discontinued." While most practitioners attending the session said they use SAA regularly, how they apply the test varies markedly depending on the type of practice. Pusterla, Javsicas, and veterinarians in the audience listed examples of how they've used SAA in everyday equine practice: ■ Differentiating between equine asthma and other upper respiratory conditions (bacterial or viral). In the former, SAA should be 0, where- as it will likely be elevated in association with infectious causes. ■ Differentiating between guttural pouch disease (usually caused by bacteria) and inflammatory airway disease (lower airway inflamma- tion, caused by allergies, bacteria, or viruses) in young racehorses as potential causes of poor performance. ■ Intensive, time-consuming colic cases that are notoriously expen- sive to treat. If SAA levels start to decrease from 2,000 to 1,000— suggesting inflammation is subsiding and the case is likely moving in a positive direction—this information might help owners make the decision to forge ahead with treatment to ultimately save the horse. ■ In healthy horses either pre-surgically (e.g., for osteochondritis dis- secans or chip fracture removal) or during a prepurchase examina- tion. Knowing a horse's SAA value when he's healthy provides a baseline should he become ill in the future. ■ Routine screening in neonatal foals to predict health issues. This seemed particularly useful on farms that regularly deal with Rhodo- coccus equi in foals. In addition to daily temperature checks, if the SAA values began to rise, veterinarians pursued further diagnostics and prescribed antibiotics for the affected foals, rather than treating all foals preventively. ■ Before or after transport (to help identify horses that might need to be isolated at their destinations). Vets deemed SAA particularly useful for horses considered at high risk for infection—those that are competing and stressed or that were recently ill—to help decide whether they have recovered sufficiently to handle shipping stress. ■ During disease outbreaks such as influenza and equine herpesvirus, even testing healthy horses, to better control the outbreak and group or isolate horses appropriately. As for specific SAA numeric values and what they mean, Pusterla said, "The kinetics of inflammation vary so immensely between different disease processes, so it's hard to say what a 'significant' increase or decrease is." Instead of relying on an exact SAA numeric value as an indicator of a clinical problem, Pusterla said he looks to trends. For example, he starts "getting nervous" with levels higher than 1,000 and will continue to monitor SAA values to assess that horse's response to therapy. During the session Pusterla pointed out the importance of not be- coming reliant on a single diagnostic test, even one as black-and-white as SAA. In addition, he recommended veterinarians read the manual before using this stall-side test and have all the equipment they need before starting, including extra batteries, lens cleaners, and swabs. When monitoring a single patient's SAA levels, use the same sample each time (whole blood vs. plasma vs. serum), and read the result at exactly the recommended duration, as the test results will continue to change over time.—Stacey Oke, MSc, DVM

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