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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TheHorse.com | The Horse February 2019 23 the most commonly reported form of laminitis," says Coleman. "Recent stud- ies have highlighted the role of excess circulating insulin in the bloodstream (hyperinsulinemia) as a risk factor for (its) development. "In a recent study … risk fac- tors for development of pasture- and endocrinopathic-associated laminitis include obesity, prior diagnosis of meta- bolic disease, and recent corticosteroid administration," she adds. Linton sums up the likelihood of a co- morbidity that includes laminitis: "Lami- nitis is a complex disease process, and its relationship to other disease complexes may have different causes." She lists the possible relationships between obesity, insulin dysregulation, and laminitis: ■ Insulin dysregulation impacts nutri- tion, health, and hoof cell function, leading to laminitis. ■ There is a relationship between obesity- induced chronic systemic inflamma- tion and inflammatory molecules in the blood and the hoof. ■ Insulin dysregulation changes blood vessels and blood flow in the hoof. Coleman also describes how lamini- tis is associated with sepsis (a systemic inflammatory response to infection) in adult horses. This is often a complica- tion of diseases such as gastrointestinal (GI) tract twisting (strangulation), colon inflammation (colitis), complicated bacte- rial pneumonia (pleuropneumonia), and uterine infection. "Carbohydrate overload, such as might occur from excess grain ingestion, is asso- ciated with disruption of the bowel lining, potentially leading to leakage of toxins and inflammatory components into the systemic circulation—this can predispose to laminitis," she says. "Additional studies have noted altera- tions in cecal and colonic microflora and pH due to carbohydrate-rich diets," she continues. "This may increase systemic absorption of triggers to laminitis. "Alterations in the GI tract that increase intestinal permeability are known as 'leaky gut,' " Coleman adds. This compromises the intestinal barrier's protection against harmful toxins. She says leaky gut results from a variety of conditions, including physical stressors, decreased blood flow to the intestine, inflammatory GI disease, and infections. It can result in systemic inflammation affecting multiple organ systems. "Increased risk of infection can be life-threatening, while laminitis can be a debilitating disease in the advanced stages or when it becomes uncontrolled," says Linton. Similarly, a horse that's undergone successful surgical treatment for strangu- lation colic could still ultimately succumb to the effects of laminitis, says Coleman. Lung Disease Typically, equine asthma is a result of allergens that trigger lung inflammation, which can lead to systemic inflammation and resulting multimorbidity. Coleman says that in human asthma systemic involvement is associated with increased inflammatory markers in the blood. These include inflammatory pre- cursors, called cytokines, and acute phase proteins, which the liver produces and are known to rise very rapidly in response to infection and inflammation. "Comparison of acute phase proteins and cytokines in healthy horses and horses with equine asthma holds some promise for markers of acute and chronic systemic inflammation," she says. Lyme Disease and EPM Clinical signs of Lyme disease caused by tick bite inoculation with Borrelia burgdorferi bacteria could be associated with co- or multimorbidities because it creates complex signs in various organ systems. Lyme disease can affect the heart, joints, eyes, muscles, respiratory tissues, and nervous system, along with behavior. Despite multiple physical signs, all aberrations can be assigned to one disease. The same applies for equine pro- tozoal myeloencephalitis (EPM)—one or several lesions from Sarcosystis neurona or Neospora hughesi protozoa in the spi- nal cord can make the horse appear to be affected by more than one disease when, in fact, the source is EPM caused by those pathogens. It's possible for horses affected by either Lyme disease or EPM to also be affected by other infectious diseases. Take-Home Message Horses—particularly aging ones—can be plagued by two or more health prob- lems simultaneously. Systemic diseases such as PPID and laminitis are two con- ditions commonly accompanied by a vari- ety of others, and they might contribute to myriad disease problems. It is important that you and your vet- erinarian try to track down all abnormal issues in your horse to be sure you treat the primary cause. Owners can help their vets sleuth the problem(s) by providing a complete history. Keep a log detailing any subtle or overt behavioral or physical changes in your horse, and share it with your veterinarian to ensure a thorough clinical workup. The best resolution comes with early diagnosis. h Disease Detection There are not many reliable stall-side tests for identifying comorbidities specifically, says Michelle Linton, BVMS, Dipl. ACVIM, staff veterinarian at the University of Pennsylvania School of Veterinary Medicine's New Bolton Center, in Kennett Square. "The best indicator is to watch for any changes in your horse's behavior," she says. "Monitoring weight changes and body fat distribution is critical. If you're spending a lot of time with your horse, subtle changes may be difficult to detect, so tools such as weight tapes and photo documentation are useful. Observe your horse for signs of secondary infection, such as nasal discharge." She says serum amyloid A (SAA), measured easily using a stall-side test, is an excellent marker of acute systemic infection; however, not all inflammatory conditions influence SAA. Linton recommends having your vet run general screening blood tests—white blood cells and inflammatory markers—to look at overall systemic status that he or she can monitor for signs of infections. Specific serologic and endocrine tests can help veterinarians accurately diagnose many equine diseases, including those that lead to comorbidities, such as PPID. "In horses with laminitis, radiographic assessment of the feet is important for ensuring stabilization of the condition and to assist with farriery care," she says. "Your horse should also have a dental exam performed by a veterinarian every six months, as this could provide a tipoff about head and sinus issues related to immune suppression by PPID."—Nancy Loving, DVM

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