Equine Metabolic Syndrome Flashcards
Obesity in horses
- potentially associated with modern husbandry
- Limited physical activity
- Over-feeding
Equine Metabolic SYndrome
- Describes a clustering of obesity
- Generalized or regional
- Insulin resistance (IR)
- Prior or current laminitis**
- Diet appears to play an important role
What are the three components of equine metabolic syndrome?
- Increased adiposity
- Hyperinsulinemia
- Insulin resistance
Age of horses affected by Equine Metabolic Syndrome
- 6-20 years old
Sex of horses affected with EMS
- No predilection
Breeds associated with EMS
- Ponies, Morgans, Paso Finos, Arabians, Saddlebreds, Quarter horses, and Tennessee Walking Horses
- “Easy Keepers”
Other components of EMS
- Dyslipidemia
- Abnormal blood adipokine concentrations
- Systemic inflammation
- Seasonal arterial hypertension
Most common presenting complaint with EMS
- Laminitis*
- Typically develops after animals have been grazing on pasture
Is adipose tissue metabolically active?
- YES
EMS typical BCS and other physical exam findings
- Severely affected horses have a BCS of 8 or 9
- Marked expansion of neck crest
- Regional adiposity score of 1-5 (scores of 3 or more often seen in EMS)
- Preputial (obese geldings have preputial adipose tissue expansion and reduced lymphatic return) or mammary gland swelling (mares)
Laminitis in EMS
- Thought to be catastrophic, but milder forms tend to be in EMS horses and ponies
- Divergent growth rings are noted in these animals
Genetics and EMS
- Some horses and ponies appear genetically predisposed to EMS
- Anecdotal reports of EMS in related horses and ponies
- Dominant pattern of inheritance for laminitis in ponies with EMS
EMS and weight
- Horses with EMS appear to require fewer calories to maintain body weight
- Indicating enhanced metabolic efficiency
- Genetic predisposition for obesity may involve specific gene mutations
- concept of “thrifty genes”
Insulin dysregulation in horses with EMS
- Assumed that insulin dysregulation results form increased pancreatic insulin secretions in response to insulin insensitivity
Glucose concentrations in horses with EMS
- NORMAL**
What’s the primary difference between EMS and diabetes mellitus?
- Diabetes refers to inadequate insulin response from the pancreas and higher glucose concentrations detected
- Not as common, but does occur
Liver changes in EMS
- Some horses with EMS have higher GGT and AST and triglycerides
- Lipid accumulation in hepatocytes
- Can have hepatic lipidosis similar to humans with fatty liver
- Reduced insulin clearance by the liver is manifested by hepatic insulin dysregulation
What mechanisms of insulin resistance exist in EMS?
- Defects in insulin receptors
- Defects in insulin signaling pathway
- Defect in glucose transporter 4 (Glut 4) synthesis, translocation, or function
How does insulin get glucose into cells?
- Insulin stimulates glucose transport into cell membranes
- Via Glut4 transporters in cell membranes
- Results show translocation impairment of Glut4 transporters
What adipokines are released from adipocytes that contribute to inflammation?
- Leptin
- Resistin
- Adiponectin
Cresty neck and inflammation
- Higher mRNA expression of IL-1beta and IL-6 in nuchal ligament adipose tissue
- Helps support the cresty neck being important
- Variety of research have had variable results
When is leptin released, and where is it released from?
- Released by adipose tissues when energy supplies are plentiful
Adiponectin role
- Considered an insulin sensitizing adipokine
- blood concentrations are positively correlated with insulin sensitivity in humans and animals
Adiponectin levels in obese horses or horses with systemic inflammation
- Lower concentrations
- No way to test this really
What receptors respond to leptin?
- Receptors in the hypothalamus respond to circulating levels of leptin
- Both appetite stimulating and satiety neurons express leptin receptors
What does activation of leptin receptors do?
- Causes down regulation and suppression of appetite
- Don’t seem to work well in horses with EMD
Leptin levels in horses with insulin dysregulation
- Tend to be higher
- Possible leptin resistance?
- Hyperleptinemia has been associated with obesity
Screenings tests for EMS
- Historical information
- Owner reports horse is an “easy keeper”
- +/- history of laminitis
PE signs of a horse with EMS
- Obese (BCS >7/9)
- Pronounced neck crest (score >3/5)
- Other evidence of regional adiposity (tail head, prepuce, mammary gland)
- Divergent growth rings (founder lines) or lameness associated with laminitis
Resting insulin test type
- Screening test
Method for resting insulin test
- Can have hay in the morning
- No feed for 4 hours and NO GRAIN OR CARBOHYDRATES
- Collect blood in AM
- Glucose concentrations above reference range of >110mg/dL
- Fasting insulin concentrations >50uU/mL
What would you expect the result of a resting blood glucose and insulin level to be for EMS?
- Hyperglycemia and hyperinsulinemia
Why do an ACTH test in a horse you think might have EMS?
- Rule out PPID
Leptin test overview
- Fasting leptin concentration >7 ng/mL (diagnostic?)
- Keep sample cool
Triglyceride levels in horses with EMS
- Shown to be elevated in horse/ponies with EMS
Dynamic oral glucose test procedures
- Oral glucose test (fast horse before testing AKA leave one flake of hay after 10 pm)
- Owner administers Karo Light Corn Syrup orally using two 60 mL catheter tip syringes
- Collect blood sample 60-90 minutes later for insulin and glucose
- Insulin values >45 uU/mL at either time point is insulin resistance
Insulin tolerance teset
- No fasting required
- Only need a glucometer
- Fed pasture or hay
- Collect blood at time 0
- Administer 0.1 IU/kg regular insulin
- Collect blood 30 minutes later
- Measure glucose and feed immediately
- <50% decrease in blood glucose = insulin dysregulation
Which test is the gold standard for EMS diagnosis?
- Combined glucose-insulin test
- NOT PRACTICAL IN THE FIELD
Combined glucose-insulin test procedure
- Perform on a fasted horse (1 flake of hay after 10 pm)
- Obtain a pre-infusion sample to measure baseline glucose
- Inject 150 mg/kg bw 50% dextrose solution IV immediately followed by 0.1 U/kg BW regular insulin
- Collect blood repeatedly (basically every 10-15 minutes until you hit 2.5 hours)
- Measure insulin at 45 minutes
Insulin resistant test result in combined glucose-insulin test
- Insulin resistant if the blood glucose concentration is above baseline or insulin concentration is greater than 100 uU/mL at 45 minutes
Should you manage EMS if you diagnose it? -
- Yes
- manage with diet, housing, and exercise intervention
2 Principle strategies of management for EMS
- Induce weight loss
2. Improve insulin sensitivity
Diet changes for EMS
- diet consisting of hay plus vitamin/protein/mineral supplement
- Should receive hay in amounts equivalent to 1.5% of IDEAL body weight per day
- Lower to 1.2% of initial BW after 1 month if no weight loss
- Minimum amount recommended is 1.2% of BW/day
Exercise program recommended for weight loss for EMS
- Increased exercise promotes weight loss by increasing energy expenditure
- 4-7 days a week for a minimum of 30 minutes excluding warm up or cool down
Hay analysis for EMS
- Analyze for carbohydrates
- Select Hay with a NSC (Non-soluble carbohydrates) of <10% depending upon the severity of IR and hyperinsulinemia in the animal
Which animals is it most important to do a hay analysis?
- Very important in managing ponies and horses with fasting hyperinsulinemia >100 µU/mL
Pasture access recommendations for horses with EMS
- Free pasture access can cause many horses predisposed to EMS to become obese
- Must limit this
- Strategies include <1 hr turn out period 2x day
- Confinement in a small paddock or round pen or enclosed area - dry lot
- Use of grazing muzzle
Levothyroxine for treatment of EMS
- High doses can induce weight loss in horses
- Accompanied by increase in insulin sensitivity
How does levothyroxine work?
- induces weight loss via raising circulating levels of thyroxine and stimulating basal metabolic rate
What other therapies must also be recommended with levothyroxine?
- Weight loss enhanced by increase in exercise and calorie restriction
- No pasture grazing should be permitted
Metformin hydrochloride
- Biguinide administered to control hyperglycemia and increase tissue insulin sensitivity in humans
How does metformin work?
- Suppresses hepatic glucose production by activating AMP-activated protein kinase
- Inhibits gluconeogenesis and lipogenesis
What cases might you use metformin in?
- Refractory cases
- Extremely obese horses
Dose timing for metformin
- 1/2 hr before feeding up to 3x per day
