IN-DEPTH: PREVENTATIVE MEDICINE: BEING PROACTIVE IN PRACTICE
mia and increased frequency of laminitis in Arabian horses10 and with height andmetabolic traits inWelsh ponies and Morgans.11,12 Future research may lead to genetic testsfor a riskofEMS, butitis likely thatother developmental, environmental, and management fac- tors play a strong role in expression of disease.
Environmental and Management Risk Factors
Not all horses with a genetic predisposition for EMS develop the syndrome. Additionally, horses with low genetic risk can develop EMS with sufficient environ- mental or management risk exposure, such as a diet high in nonstructural carbohydrate (NSC) concentra- tions and prolonged obesity. Extrinsic risk factors are more accessible to control than genetics and thus are a more useful focus for prevention of disease. Increased adiposity in the form of generalized obe-
sity or regional adiposity is frequently associated with EMS. As horses with lean body condition can also de- velop ID and laminitis, increased adiposity is not nec- essary for a diagnosis of EMS but is considered a strong risk factor. As horses age, there is a shift in bodymass compositionwithanincrease infat accu- mulation in adipose tissue and muscle.13 A decrease in basal metabolic rate as part of the normal aging process, without a concurrent decrease in appetite, may predispose older horses to excess energy intake and storage as adipose tissue. Adipose tissue plays an active role in regulation of adipokines, and inflamma- tory mediators and increased adiposity can lead to dysregulation of these systems. Leptin is an adipo- kine produced by adipocytes, and its serum concen- tration increases with increasing body condition in horses.14,15 Under normal conditions, leptin serves to suppress appetite and increase energy expenditure in the presence of excess energy stores. Leptin resist- ance appears to occur in some horse with EMS, reflected by serum leptin concentrations higher than that expected for their body condition, which might lead to increased feed intake and further weight gain.16 Adiponectin is another fat-derived hormone that functions to enhance insulin sensitivity. In peo- ple and horses, adiponectin concentrations decrease with increased body condition and fat mass.15,17 Insulin dysregulation is a central feature of EMS
and a consistent risk factor for development of lamini- tis. IDis defined as any combination of resting hyperin- sulinemia, a hyperinsulinemic response to intravenous or oral glucose, and tissue insulin resistance.4 Many studies have found that feeding diets high in NSCs result in decreased insulin sensitivity and adiponectin concentrations.18–21 The gastrointestinal microbiota has been implicated in the development ofmetabolic disease and obesity in people22 throughmodulationofenergy metabolism, gastrointestinal permeability, regulation of gastrointestinal peptide hormone secretion, and inflam- mation.23 Studies in horses have shown differences in the microbiota of horses with and without EMS or obe- sity.24–26 Recent research has investigated the micro- biome, metabolome, and lipidome of obese horses to set
402 2022 / Vol. 68 / AAEP PROCEEDINGS
a foundation for developing diagnostic biomarkers and therapeutics for obesity andEMS in horses.23 Age has been shown to have an effect on insulin
and adiponectin concentrations in horses. Older horses are more likely to have higher insulin concen- trations and lower adiponectin concentrations than younger horses and ponies, correlating with a higher incidence of EMSand laminitis in older horses.27–30
3. Diagnosis
Early detection of EMS is essential for prevention of uncontrolled disease and laminitis. As understanding of the pathophysiology of EMSis rapidly evolving, rec- ommendations for diagnosis have changed frequently in recent years. Recent consensus recommendations for diagnosis of EMS have been published and well discussed elsewhere.2,4 Briefly, basal testing of serum insulin can be useful to identify individuals with resting hyperinsulinemia but is of low sensitivity.2 Dynamic testing, measuring glucose and insulin response to an intravenous or oral glucose challenge, can be useful to help identify individuals with postprandial hyperinsu- linemia and to evaluate tissue insulin sensitivity. The oral sugar test is practical for use in the field setting. Quantitative testing for ID of at-risk individuals is highly recommended. Detection of subclinical ID allows for treatment strategies to be initiated prior to an onset of laminitis. Regular follow-up testing using the same diagnostics will allow for early detection of ID in previ- ously normal at-risk individuals and/or monitoring response to treatment. In older horses, diagnostic testing for PPIDis also recommended, especially in lean individ- uals in which ID is diagnosed. Consensus recommenda- tionsfor diagnosisofPPIDhave been published.31
4. Management
Once a horse has been identified as at risk of develop- ment of EMS, or has been diagnosed, management strategies should be implementedwith the goal of pre- venting severe ID and ensuing laminitis. An individ- ual program of dietary management, exercise, and monitoring should be tailored for each horse and owner.
Dietary Management
Nutritional strategies for management of EMS should seek to maintain a lean to average body condition score and control ID. Asmany at-risk or recently diag- nosed horses are obese, weight loss is often a goal of dietary management. Feeds high in NSCs such as ce- real grains and treats including fruits and vegetables should be minimized in the diet. A key component in the success of dietary management of EMS is owner compliance, and excellent client communication strat- egies are often necessary. Multiple studies have shown that weight loss
achieved through energy restriction reduces insulin dysregulationin horses withEMS.32–35 Consensus rec- ommendations for weight loss include feeding of 1.25%
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