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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Page 21 of 51

22 February 2019 The Horse | and found that 12% of the horses experi- enced one of those diseases: cancer, PPID, equine metabolic syndrome (EMS), grass sickness, laminitis, navicular syndrome (now known as podotrochlosis), osteoar- thritis, recurrent airway obstruction, and sarcoids (Welsh et al. 2016). They identi- fied multiple chronic disease processes in 1.2% of the study population. In that study 49% of horses with comorbidities were affected by PPID. Because it's a systemic problem, veteri- narians know it is not uncommon to see PPID in concert with other conditions. Michelle Coleman, DVM, PhD, Dipl. ACVIM, assistant professor of large animal internal medicine at Texas A&M University, in College Station, describes a variety of conditions and characteristics reported in conjunction with PPID: ■ Laminitis in 24-82% of PPID horses; ■ Abnormal sweating patterns such as anhidrosis (not sweating enough or at all) or hyperhidrosis (sweating too much) in 14-67%; ■ Abnormal fat deposition in 9-67%; ■ Increased susceptibility to secondary infections in 33-55%; and ■ An association with suspensory liga- ment degeneration. The increased infection susceptibility is due to reduced immune responses, says Michelle Linton, BVMS, Dipl. ACVIM, staff veterinarian at the Univer- sity of Pennsylvania School of Veterinary Medicine's New Bolton Center, in Kennett Square. "Studies have shown that some cells responsible for a healthy immune system don't function adequately in hors- es with PPID," she says. "Therefore, these horses are at higher risk for any type of infection, including skin infections, foot abscesses, dental disease, sinusitis, con- junctivitis, and pneumonia." If horses with PPID do develop infec- tions or wounds, these altered immune responses can make healing challenging. Obesity and Endocrine Disease Obesity leads to many significant health problems, including insulin resis- tance (IR, a reduced sensitivity to insulin that results in high blood insulin levels) or insulin dysregulation, EMS, low-grade systemic inflammation, laminitis, and fertility issues. Horses with EMS are typi- cally overweight with a body condition score above 6 or 7 (on a scale of 1-9) and obvious fat deposits along the neck, loins, shoulders, sheath, or udder, for example. They are usually middle-aged. "We refer to EMS horses as having insulin dysregulation rather than just resistance," says Linton. "The term dys- regulation better describes these indi- viduals' abnormally high resting insulin blood levels, abnormal insulin responses to feeding and glucose administration, and tissue insulin resistance." Coleman emphasizes, however, that not all obese horses are insulin-dysregulated and not all insulin-dysregulated horses are obese. "PPID and EMS are both endocrine diseases, so one disease/syndrome could make the horse at higher risk for developing the other," says Linton. Only occasionally does she see a PPID horse develop EMS. "More often," she says, "we see that some horses with EMS subse- quently develop PPID." Coleman concurs, adding that horses with EMS might be at greater risk of developing PPID as they age and should be monitored and tested for it. "In people, there's a link between obesity and inflammation, which is involved in the (development) of several chronic diseases," says Linton. "The same can be said for horses, with research now identifying that obesity-induced chronic inflammation identified in the bloodstream may lead to development of inflammatory conditions such as osteoarthritis." Studies in humans and rats have shown that low-grade inflammation initiated by obesity can transfer from mother to offspring. Similar issues have emerged in equine studies: Maternal obesity in mares alters metabolism, increases the likeli- hood of insulin resistance, and increases low-grade systemic inflammation in both dams and foals. Inflammatory effects in the brain can lead to anxiety, behavioral abnormalities, and learning difficulties. In one study more foals born to obese mares developed osteochondrosis in joints than did foals born to nonobese mares. Laminitis In the aforementioned U.K. study of more than 100,000 horses, the authors noted that 74% of multimorbidity cases involved laminitis, which is often a sys- temic disease coupled with a number of physiologic derangements. In affected horses the tissues that attach the hoof to the coffin bone within fail, possibly re- sulting in rotation or sinking of the bone. "Laminitis development in the context of underlying endocrinopathic disease (i.e., EMS or PPID) has been referred to as endocrinopathic laminitis and is A Closer Look at Comorbidities Obesity has been linked to a variety of other health problems, including insulin resistance, equine metabolic syndrome, inflammation, laminitis, and fertility issues. ISTOCK.COM In a recent study 74% of multimorbidity cases involved laminitis

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