The Horse

FEB 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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32 February 2019 The Horse | of the WALTHAM Equine Studies Group, in Leicestershire, England. Researchers have conducted many studies on obesity prevalence in equids, and the findings shed clear light on a problem: ■ In one study of 319 pleasure horses in Scotland, researchers classified 45% of the animals as fat or obese; ■ In two U.S. studies scientists classified 48% of 366 North Carolina horses as overweight or obese and 51% of 300 mature Virginia horses as such; ■ In a study of 127 U.K. horses and ponies living at pasture for at least six hours per day, scientists classified 28% as obese at winter's end and 35% as obese at summer's end; and ■ In a study of 300+ horses in a U.K. championship, 41% were overweight and 21% were obese, with show and dressage horses most likely overweight. Why are so many horses obese? Some factors include: ■ Breed In a U.K. study native breeds and cobs were 14 times more likely to be obese than other breeds. ■ Pasture "In the U.K. many fields now used for horse grazing used to be grazed by dairy cows, and we're putting native breeds out on these potentially energy-rich pastures," Harris said. "(Here) it is possible for a 300-kilogram (660-pound) pony to ingest the same number of calories as a 500-kilogram (1,100-pound) racehorse in training." ■ They become wise to their routine Even if an owner is trying to limit grass intake, their horse or pony might have "wised up to this," Harris said. By Week 5 of limited daily pasture turnout, "ponies ingested an estimated 40% of their daily dry matter intake in grass in three hours—and work has shown that ponies can ingest almost 5% of their body weight in dry matter (all nutrients minus water) per day and more than 1% of their body weight in dry matter during a three-hour turnout on pasture, which is all that would be recommend- ed … on a severe weight loss restriction diet," Harris said. ■ Too many calories and not enough exercise Researchers and veterinar- ians have observed that owners often don't feed for the exercise level they're undertaking or believe their horses are working harder than they are and, so, require more calories than they do. Perhaps the biggest issue with obesity, Harris said, is some owners don't recog- nize it. In one study of nearly 550 owners, only 11% correctly identified all the examples of overweight horses shown. Gastric Ulcers in Horses We know an estimated 50-90% of horses suffer from ulcers and that per- formance and racehorses are some of the most susceptible. Al Merritt, DVM, Dipl. ACVIM, a professor emeritus at the Uni- versity of Florida College of Veterinary Medicine, in Gainesville, described what researchers have learned about equine gastric ulcers in the past three decades. Horses produce gastric acid con- tinuously, whether they're eating or not. When they chew, their bodies release saliva, which contains sodium bicarbon- ate and calcium—both of which buffer stomach acid. This is good if horses are grazing continuously, but human man- agement can put a wrench in the gears. When we supply horses with a few meals a day, the stomach keeps producing acid, but there's not a steady saliva sup- ply. This leaves the stomach to become increasingly acidic and raises ulcer risk. Ulcers weren't always at the top of vets' differential diagnoses when health problems arose. But with the discovery of gastric lesions on necropsy findings in the mid-'80s, followed by the develop- ment of endoscopes (long, flexible tubes with cameras attached), veterinarians began to conduct gastroscopy. During this procedure a veterinarian passes the tool through the horse's nostril, down the esophagus, and into the stomach to peer inside it. This is the only definitive way to diagnose gastric ulcers. Eventually, scien- tists developed videoendoscopes. Vets realized ulcers were significant problems for high-performance horses, and researchers began studying them more. In 1999 the Equine Gastric Ulcer Council published its recommendations for diagnosing and treating equine gastric ulcer syndrome (EGUS), introducing the now-common term. Common clinical signs included poor appetite; dullness; attitude changes; decreased performance; poor body condi- tion; and low-grade colic. While these signs still point to ulcers, Merritt noted that "we know now that they don't even have to show signs to have gastric ulcers." Around that time two gastric ulcer scoring systems were introduced to grade squamous lesions, with a five-point sys- tem (0 to 4) catching on best. Newer Research Key developments since 1999 include: ■ Scientists learned that ulcers aren't just a problem for horses in training when they identified lesions in 16 of 17 horses stabled full-time, 125 of 141 horses turned out on pasture for at least four hours each day, and in all 13 horses turned out full-time; ■ Researchers split EGUS into two cate- gories: equine glandular gastric disease (EGGD, the lower half of the stomach) and equine squamous gastric disease (ESGD, the less-protected upper half); ■ Scientists found that the pH within the squamous part dropped below 4 (the "cutoff" for when the pH is corrosive to the lining) when horses began trotting and continued into gallop; it then rose when the horses walked; ■ The same team determined that intra- abdominal and intragastric pressure increased during exercise, which likely pushes the glandular region's contents (including gastric acid) up into the unbuffered squamous area; ■ Horses were more likely to have both EGGD and ESGD if they ate large amounts of concentrates; ■ Scientists identified other potential gas- tric causes as stress and meal-feeding; DIETARY DEVELOPMENTS These EGGD lesions are visible via videoendos- copy of the stomach's pyloric glandular region. COURTESY DR. AL MERRITT

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