The Horse

APR 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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Inquiries to: 859/276-6726 E-Mail: News@TheHorse.com ERICA LARSON, News Editor @TH_EricaLarson 8 April 2019 The Horse | TheHorse.com Rikke Buhl, DVM, PhD, of the University of Co- penhagen's Department of V eterinary Clinical Sci- ences, in Taastrup, Den- mark, and her colleagues used electrocardiography (ECG, which measures the heart's electrical activity) to evaluate heart rates and abnormal beats in Standardbred racehorses— which are eight times more likely to have atrial fibrilla- tion than the general horse population (TheHorse. com/137150). They were "extremely surprised" with the results. "Previously I hadn't been too worried about people riding or driving horses suffering from atrial fibril- lation, but after this study I am more concerned," she said. Buhl's team exercised nine healthy, recently retired Standardbred racehorses on a treadmill to evaluate their cardiac function and performance. Then they induced atrial fibrillation and repeated the treadmill test (learn more about the materials and methods at TheHorse. com/165498). Horses with atrial fibril- lation had a 12% reduction in blood flow velocity compared to controls. Stud- ies in humans suggest this corresponds to a roughly 15% reduction in exercise capacity, Buhl said. What's more, they noted maximum heart rates as high as 346 beats per minute (bpm) in the atrial fibrillation group; a normal, healthy exercising heart rate hovers around 200 to 240 bpm, they said. Ultimately, the team con- firmed that atrial fibrilla- tion resulted in significantly reduced performance, substantially increased heart rates, and frequent abnormal heartbeats during exercise, which could put the horse at risk for collapse or sudden cardiac death. "The results are disturb- ing," she added. "Based on what we've seen, I now always recommend several exercise tests for horses, equipped with ECG readers, before I recommend riding or driving the horse suffer- ing from atrial fibrillation." —Christa Lesté-Lasserre, MA T he athletic future of a horse diagnosed with atrial fibrillation can be uncertain; his blood courses through his cardiovascu- lar system slower than in a horse without, and his heart beats faster. Until recently researchers had never quantified just how seriously this car- diac arrhythmia affects heart function, giving them a realistic look at the dangers the condi- tion poses. How Atrial Fibrillation Impacts Performance Researchers used retired Standardbred racehorses to study the effects of atrial fibrillation on heart function and athletic performance. COURTESY DR. RIKKE BUHL NEWSFRONT Certain Environmental Chemicals Linked to EMS Researchers recently confirmed that endocrine-disrupting chemicals (EDCs) in a horse's environment—think pesticides, plastics, and personal care products—could play a role in the development of equine metabolic syndrome (EMS). This finding could help explain some of the variability in EMS severity that can't be explained by diet, exercise, season, and other factors. "This is a pivotal piece of a very complicated jigsaw puzzle," said Molly McCue, DVM, MS, PhD, Dipl. ACVIM, of the University of Minnesota College of Veterinary Medicine, in St. Paul. "There are a lot of horse own- ers out there who are very diligent about providing their horses fantastic care, but the horse is still diagnosed." Man-made EDCs are prevalent in the environment and can mimic a body's hormones and block them from doing their jobs. McCue said it remains to be seen how significant the association between EDCs and EMS development is, but she hopes future studies will further scientific understanding and help advance equine veterinary care. Sycamore Toxin Disease Kills Newborn Foal Researchers described what they believe to be the first reported case of a neonatal foal dying due to atypical myopathy (AM)—an often-deadly muscle disease of horses in the U.K. and the rest of Europe caused by a toxin found in sycamore tree seeds. The filly was born to a mare that developed AM when she was six months pregnant and recovered before delivering full-term. The filly suckled within two hours of birth but appeared weak six hours postpartum. Blood tests confirmed AM, and she was eventually euthanized. It's unclear if the toxin passed through the placenta in utero or through the mare's colostrum. But, said Petr Jahn, PhD, of the University of Veterinary and Pharmaceutical Sciences Faculty of Veterinary Medicine, in the Czech Republic, the latter seems more likely: "In the case of transplacentar trans- mission of the toxin during pregnancy, I would expect abortion." STUDY SHORTS

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