The Horse

MAR 2018

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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SPONSORED BY A51 TheHorse.com/AAEP2017 March 2018 THE HORSE AAEP Wrap-Up Léguillette said. Common signs of an up- per airway issue include: ■ Abnormal respiratory noise; ■ Exercise intolerance; and ■ Coughing. Lower airway problems are often char- acterized by: ■ Coughing; ■ Nasal discharge, usually bilateral (from both nostrils) and mucousy; ■ Exercise intolerance; and ■ Labored breathing at rest. "Studies have shown that owners are a good and reliable source for observ- ing changes in their horses' respiratory signs," Léguillette added. Specifically, researchers found that owners are better than vets at detecting changes relating to their horses' cough- ing, he said. One study that showed: ■ Horses that cough frequently or constantly and during exercise are more likely to have severe airway inflammation; and ■ Horses that cough more frequently at the start of exercise are likely to have moderate to severe inflammation. "I think it is therefore important to not ignore coughing observed at the begin- ning of exercise," Léguillette said. After evaluating clinical signs, the vet- erinarian has several diagnostic options: Endoscopy Static (at rest, in a standing horse) and dynamic (during exercise, as seen in the photo to the left) upper airway endoscopy can help diagnose obstruc- tions, Léguillette said. Such issues can include laryngeal hemiplegia (roaring), dorsal displacement of the soft palate, and pharyngeal collapse. Upper and lower airway endoscopy can also show evidence of EIPH, mucous ac- cumulation (due to lung inflammation), and pharyngitis (pharynx inflammation). Thoracic ultrasound Most useful for assessing the lung surface and diagnosing pneumonia and related issues, ultrasound of the horse's chest can also reveal evi- dence of EIPH, Léguillette said. Radiographs Although difficult to per- form on full-sized horses in the field, due to the lungs' large size, X rays can help vets see the deeper lung structures, along with evidence of EIPH and pulmonary nodular fibrosis, he said. However, they lack the sensitivity (the probability that results will be correctly positive) needed to diagnose inflammatory disease. Sampling to detect inflammation Vet- erinarians can collect a variety of samples from the respiratory tract, Léguillette said. These include tracheal wash and/ or bronchoalveolar lavage (BAL) samples (flushing saline into the windpipe and drawing the "wash" back up with a syringe, or lavaging a lung with sterile fluid before drawing it back out again, respectively). Practitioners examine both types of samples under a microscope to detect signs of inflammation. Léguillette said BAL analysis is the more reliable of the two for detecting lung inflammation. However, he added, it isn't always clear- cut, because some horses have persistent inflammation even after treatment. Lung function testing These tests are difficult to perform in the field and are most commonly used in research settings, he said. They include bronchoprovo- cation tests (to assess the respiratory system's response to bronchoconstrictive agents) and measuring VO 2 max. "Diagnosing pulmonary pathologies in athletic horses can be challenging and should start with a good documentation of clinical signs," Léguillette said. "The inter- pretation of ancillary tests can be difficult if a good technique is not used properly." Consider History, Environment When Managing Equine Asthma On the surface, managing equine asthma—including RAO, a chronic condi- tion common in older horses, and IAD, often seen in younger equine athletes— might not seem complicated: Modify the horse's environment and treat, when needed, with corticosteroids and broncho- dilators. In reality, it can be challenging. Furosemide Administration Times Tested Thoroughbred racehorses in North America often receive furosemide as a preventive for exercise-induced pulmonary hemorrhage (EIPH, bleeding into the lungs). An estimated 44- 75% of Thoroughbred racehorses suffer from this condition, which can adversely affect both health and performance. Typically given four hours before a race, furosemide is currently the only proven preventive treatment available. Under the pending Horseracing Integrity Act of 2017 (HR 2651), race-day furosemide administration might be banned due to concerns that it might mask illegal substances. In anticipation of this legislation, researchers from the University of California, Davis, looked at furosemide's ability to reduce EIPH in Thoroughbred racehorses when adminis- tered 24 hours vs. four hours prerace. Anecdotal reports suggest that administering the drug 24 hours prerace might be as effective as race-day administration in decreasing EIPH sever- ity. Associate professor Heather Knych, DVM, PhD, Dipl. ACVCP, presented their findings. The team used 15 client-owned Thoroughbred racehorses, both male and female, ages 2 to 4, whose EIPH status was unknown. They randomly assigned horses to one of three treat- ment groups: 250 mg of intravenous (IV) furosemide 4 hours before exercise, 250 mg of IV furosemide 24 hours before exercise, or 5 mL of 0.9% IV saline as a control. They restricted horses' water access four hours before a five-furlong simulated race on a synthetic or dirt track. All horses underwent a two-week washout period before moving to the next treatment. The researchers noted a significant difference in EIPH scores after four-hour and 24-hour furosemide administration. When horses received furosemide four hours before exercise, 93% had a zero EIPH score (no blood detected in the pharynx, larynx, trachea, or main- stream bronchi) one hour post-exercise versus 60% when furosemide was given 24 hours before exercise. Sixty-nine percent of the saline-treated horses had a zero score. An investigator blinded to the treatment also performed bronchoalveolar lavage (BAL) and counted the number of red blood cells (RBC) in the BAL fluid. Horses receiving furose- mide four hours before exercise had significantly fewer RBCs in their BAL fluid than when they received saline, but there was no significant difference between saline and 24-hour furosemide treatment. Knych cautioned that the limited sample size and broad range of horses' athletic ability might have impacted treatment effect. However, she said, the results suggest furosemide is effective for reducing EIPH severity in Thoroughbred racehorses, but any reports that it's just as effective when administered four or 24 hours prerace are unfounded.—Clair Thunes, PhD

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