Ask Your Veterinarian Presented By Kentucky Performance Products: Enteroliths Can Make A Rocky Road To Colic

Veterinarians at Rood and Riddle Equine Hospital answer your questions about sales and healthcare of Thoroughbred auction yearlings, weanlings, 2-year-olds and breeding stock.

Question: How common are enteroliths, and what causes them?

Dr. Katy Dern, Rood and Riddle Equine Hospital: While many of our colic patients make it clear within a few minutes of presentation to hospital that they will require surgery — high heart rate, unremitting pain in the face of sedatives and NSAIDS, or clinical signs of devitalized bowel – some patients make it more difficult to determine if surgery is indicated. Horses with enteroliths are often on that list.

Enteroliths are calculi (rocks) which form in the right dorsal colon and can cause partial or complete obstruction of the gastrointestinal tract. They are composed of struvite (magnesium ammonium phosphate hexahydrate) and form when mineral deposition occurs in concentric layers around a central nidus. Although this central nidus is sometimes a foreign body (rope or metallic object), in most cases it is indistinguishable from the rest of the calculi.

Dr. Kathryn Dern

Although we don't know exactly why some horses form enteroliths and some don't, we do know that there are certain risk factors for enterolith formation. A review of 900 cases of horses with confirmed enteroliths determined that Arabians, Morgans, and American Saddlebreds are at an increased risk for developing enteroliths. Enteroliths were also found to occur more frequently in horses in California and regions of the Southwest. From a management perspective, the most important aspects of this retrospective analysis and other studies were that most patients with enteroliths had a diet which consisted of more than 50 percent alfalfa hay, and there was a significantly increased incidence of enteroliths in horses which did not have daily access to pasture grazing.

If your horses are part of the “at-risk” population, we recommend ensuring that the majority of their diets consist of pasture or grass hay, avoiding alfalfa-based products. Although the exact role of alfalfa in the formation of enteroliths is unknown, it is suspected that the higher protein content can result in a more alkaline pH in the colon, favoring enterolith formation. Alfalfa hay also has higher levels of magnesium and phosphorus, both of which are components of the typical struvite enterolith.

Enteroliths usually form in the right dorsal colon, which has a large enough diameter to accommodate the calculi while still allowing feed to pass through the gastrointestinal (GI) tract. If the enterolith begins to move from the right dorsal colon into the transverse colon, or further abroad into the small colon however, it becomes lodged due to the smaller diameter of these parts of the GI tract. In some horses, the enterolith intermittently occludes the transverse colon, causing occasional mild colic signs which resolve with medical management (flunixin meglumine, intravenous fluids, etc). Once the enterolith becomes lodged in the transverse or small colon, it completely blocks the passage of feed material though the GI tract, causing colic signs.

Diagnosis of enteroliths in the patients with a history of chronic colic can be challenging. Abdominal radiographs (x-rays) are more reliable in diagnosing enteroliths which are in the large colon versus the small colon – presumably due to the increased diameter of the enteroliths in the large colon. Enteroliths cannot be imaged in an ultrasonographic examination and are rarely detectable on rectal palpation. For these reasons, a definitive diagnosis of enterolithiasis often requires surgery.

In the patients with persistent colic signs in which the enterolith has become permanently lodged in the bowel, timely surgical intervention is important. In these cases, the enterolith compresses the bowel wall, decreasing the blood supply and potentially causing weakened areas or areas of necrosis (tissue death), which can lead to fatal rupture of the transverse or small colon. To avoid this tragic outcome, surgery is recommended in horses with persistent pain in the face of sedation and analgesia (flunixin meglumine, etc).

Once in surgery, the location of the enterolith is determined and a pelvic flexure enterotomy is performed to completely empty the contents of the large colon. This procedure involves making a small incision in the bowel wall through which to empty the contents, and then instilling fluid into the large colon to help “flush” the enterolith to a location from which it can be safely removed. Multiple incisions are often required to both evacuate the contents of the colon and to remove the enterolith. If the enterolith is lodged in the small colon, an incision will be made into the wall of the small colon to facilitate enterolith removal. In some cases, the enterolith has compressed the bowel wall so severely that tissue death (necrosis) has occurred – in these cases the devitalized area of bowel needs to be removed.

Post-operative management involves intravenous antimicrobials, intravenous fluids, and a gradual refeeding program to ensure that the lining of the colon has time to recover from trauma and irritation caused by the enterolith. Fortunately, survival after surgical removal of enteroliths is high, with reports ranging from 92 percent to 96 percent. As with many colic cases, prompt referral and timely surgical intervention are the keys to a good outcome.

Dr. Dern is originally from Colorado and Montana. She attended Washington State University for her undergraduate work, and Colorado State University for her veterinary degree. Following graduation from CSU in 2012, she completed an internship at Peterson and Smith Equine Hospital in Ocala, followed by an internship at Rood and Riddle Equine Hospital. After her internships, Dr. Dern completed a three-year surgical residency at The Ohio State University, while also earning a Master's of Science Degree. She became board certified in equine surgery in 2018 and has been the surgeon at Rood and Riddle's Saratoga hospital since 2017. 

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Obese Horses More Likely To Move Unevenly

In an effort to determine how added weight affects equine fitness and performance, Dr. Anna Jansson and a research team from the Swedish University of Agricultural Sciences and Hólar University published a study in Physiological Reports in which horses were fed controlled diets to add or restrict weight gain. The scientists used nine Icelandic horses that they split into two groups. Changes in body weight and fat were induced in the group being fed a high-energy diet for 36 days.

During the last seven days of the study period, researchers recorded body condition score and weight, and percentage of body fat was estimated with an ultrasound. Each horse was then given an exercise test on a treadmill and a field test that mimicked a competition, which was scored by judges. Blood samples were taken, as well as heart rate, temperature and respiratory rate.

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On the treadmill test, the horses that had gained weight had a higher heart rate and temperature, and heavier respiration. Blood tests showed that heavier horses had lower physiological fitness.

The team also found that overweight horses showed a marked gait asymmetry compared with leaner horses, as was shown both by sensors placed on the horses while they moved. The heavier horses moved most asymmetrically on the day after their field test.

Judges overseeing the field test also scored heavier horses lower than their leaner counterparts, suggesting that weight affects performance.

The authors conclude that higher body fat and body weight lowers equine performance, made horses move more unevenly, and delayed their recovery from exercise.

Read the full study here.

Read more at HorseTalk.

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Can A Mechanical Device Improve Equine Lung Function?

Humans who have chronic lung or heart disease often breathe through a device that resists inhalation to increase muscle strength. Called inspiratory muscle training (IMT), this therapeutic technique trains both the diaphragm and the upper airway muscles to become stronger, improving respiratory strength, according to EQUUS magazine.

Dr. Kate Allen of the University of Bristol wanted to see if the technique could be applied to horses. In people, respiratory performance is limited by cardiovascular capacity; in horses, athletic performance is limited by respiratory function. Using IMT to improve the fitness and function of the respiratory muscles allows them to work more efficiently.

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Allen and a study team acclimated 10 Thoroughbreds in steeplechase training to wearing a mask fitted with valves that control the level of resistance to each inhalation. The horses underwent IMT training five days a week for nine weeks. During each session, the horse took 30 resistant breaths, was rested for two minutes, then took 30 more resisted breaths, all while standing still. The resistance was increased every four days, but the trial allowed for an increase or decrease in resistance depending on how the horse tolerated the change. The horses continued normal racing and training schedules during the study, and tests of each horse's respiratory strength were made before and after the IMT.

The scientists found that horses had no issues adapting to IMT training and that it can be used on horses in competition. The next study will look at IMT training and its impacts on physiologic and performance changes in the horses.

Read more at EQUUS magazine.

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New App Allows For Real-Time Equine Temperature Monitoring, Location Dissemination And Data Sharing

Merck Animal Health has announced its strategic partnership with Irish-based technology company EquiTrace Ltd., creators of the EquiTrace™ platform. Through the EquiTrace smartphone app, the entire horse care team can securely update and access each horse's GPS location and medical record in one convenient location. The app also works in conjunction with Merck Animal Health's Bio-Thermo® microchips, allowing horse care professionals to instantly read, graph and monitor a horse's temperature.

“This partnership is a natural extension of our commitment to delivering innovative infectious disease management solutions to support improved horse care,” said Ron McDaniel, Director of U.S. Equine Sales, Merck Animal Health. “By enabling convenient digital temperature monitoring, we're able to make life easier for busy veterinary and farm teams while providing them with tools to help efficiently identify illness and monitor disease outbreaks.”

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EquiTrace, which can be used with individual horses or at large barns, is compatible with any microchip but must be coupled with a Bio-Thermo microchip to access the temperature-sensing functionality. Bio-Thermo microchips measure a horse's temperature within one-tenth of a degree[1] and provide access to a horse's identification. Both the EquiTrace app and Bio-Thermo microchips work with the Global Pocket Reader Plus™ and the HomeAgain® UWSR+ microchip readers, and the EquiTrace app is available for iPhones or Androids. In addition, the Bio-Thermo microchip is compliant with the International Organization for Standardization (ISO) Standards 11784 and 1178 and meets requirements of both the International Federation for Equestrian Sports (FEI) and the United States Equestrian Federation (USEF).

“We are excited to partner with Merck Animal Health to bring EquiTrace to the U.S.; the technology streamlines health recordkeeping, a task that has traditionally been hard to maintain in busy barns,” says EquiTrace founder Kevin Corley, BVM&S, PhD, DACVIM, DACVECC, MRCVS. “The combination of Bio-Thermo microchips with our software enables rapid identification of temperature fluctuations in a horse at the stroke of a microchip scanner. This is essential to managing infectious diseases, such as equine herpesvirus, influenza and strangles. As an internal medicine specialist, I'm delighted to contribute to a novel temperature monitoring system that's effective without stressing the horse or the barn team.”

EquiTrace data is encrypted, and each barn's data is private. The EquiTrace account owner authorizes others to access data securely through the app. All EquiTrace functions are available with no internet connection for easy access at the barn or on the road. New data is synced when the app is opened with internet connection. To download EquiTrace, visit the App Store or Google Play.

Read more here.

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