Equine Metabolic/Endocrine Disease

Question 1

What is equine polydipsia defined as?

Answer 1

> 100ml/kg/day water intake

Question 2

What is the typical signalment for Pituitary Pars Intermedia Dysfunction (PPID)?

Answer 2

Common in old-aged horses
Clinical signs in 20-30% of over 15s
Can occur in younger horses
Test all horses with laminitis unless young

Question 3

What is the mechanism of PPID?

Answer 3

Decrease in production of dopamine from hypothalamus
Decrease in inhibition of pituitary
Pituitary adenoma (micro/macro)
Overproduction of hormones

Question 4

What are the clinical signs of PPID?

Answer 4

Variable! May be no clinical signs
Long curly coat
Laminitis
PUPD
Weight loss
Docile
Neurologic impairment
Hyperhidrosis
Change in fat distribution, bulging fat pads
Infertility
Skin disease
Periodontal disease

Question 5

What is the first-line test for PPID?

Answer 5

ACTH test
Resting plasma ACTH collection - horse not stressed
Collect blood - cold, not frozen
Send plasma
Adjust reference range for autumn (when pars intermedia more active)

Question 6

What is the second diagnostic test for PPID?

Answer 6

TRH stimulation test
Use if basal ACTH borderline, not conclusive
Basal blood sample, inject TRH, blood sample again at 10 mins +/- 30 mins post-injection

Question 7

How can we manage PPID?

Answer 7

Farriery
Clipping
Parasite control
Dental care
Feeding

Question 8

How can we medically treat PPID?

Answer 8

Dopamine agonist - Pergoglide tablets
Start with 1mg/horse SID or divided BID
Monitor, adjust dose, reassess annually
May go off food - resolves on lower doses
Usually very effective

Question 9

What are the three main things seen with Equine Metabolic Syndrome (EMS)?

Answer 9

Obesity or regional adiposity
Insulin dysregulation/resistance
Subclinical and clinical laminitis

Question 10

What kind of insulin dysregulation do we see in EMS and PPID and what does this mean for blood samples?

Answer 10

Compensated:
High insulin, normal glucose
May have this at rest or only as a response to feeding

Question 11

Describe laminitis seen with EMS.

Answer 11

Clinical or subclinical

Hyperinsulinaemia is direct cause of laminitis

Question 12

What is the role of genetics in EMS?

Answer 12

Genetic predisposition for insulin dysregulation in hardy breeds
Insulin dysregulation facilitates breakdown of glucose and fat stores and stimulates hepatic gluconeogenesis
Keeps a glucose supply for vital tissues e.g. CNS
Ability to mobilise energy stores and prioritise vital tissues = survival benefit if poor diet

Question 13

How are obesity and insulin dysregulation linked?

Answer 13

Wild horses = get fat over summer (develop insulin dysregulation), lose weight in winter (restoring insulin sensitivity by spring)
Domestic horses no longer subject to seasonal weight loss, have a lack of exercise, chronic progressive obesity and laminitis ensue

Question 14

What are the clinical signs of EMS?

Answer 14

Obesity - BCS 7/9 - 9/9
Regional adiposity - cresty neck, tail head, preputial swelling/mammary glands
Subclinical/clinical laminitis
Possible related disease e.g. hyperlipaemia, lipoma

Question 15

How can we diagnose EMS?

Answer 15

Starve overnight
Blood sample glucose and insulin
Bolus glucose/corn syrup
Blood sample glucose and insulin at 2-3hrs
Hyperinsulinaemia and normoglycaemia

Question 16

How can we manage EMS?

Answer 16

Diet - low carb, no concentrate, multivitamin/mineral supplement, no grass/grass muzzle
Exercise - major effect on insulin sensitivity, but if laminitic?
Weight loss - feed 1/3 less than before, min. 1.5kg forage per 100kg, soak hay > 1hr, haynet with small holes

Question 17

How can we medically manage EMS?

Answer 17

Metformin
Increases insulin sensitivity in humans
Horses no bioavailability but blocks small intestine carbohydrate absorption
Decreases insulin dysregulation only by weight loss

Question 18

Describe hyperlipaemia.

Answer 18

Fatty acid mobilisation triggered by negative energy balance/stress (catecholamine and glucocorticoid release)

Question 19

What are the risk factors for hyperlipaemia?

Answer 19

Obesity
Ponies
Pregnant
Donkeys

Question 20

What can hyperlipaemia cause?

Answer 20

Hepatic lipidosis
Liver failure
Lactescent blood
Fat embolism
Kidney failure
Pancreatitis

Question 21

What are the clinical signs of hyperlipaemia?

Answer 21

Depression
Anorexia
Ataxia
Icterus

Question 22

How can we treat hyperlipaemia?

Answer 22

Improve energy intake and balance
Treatment of hepatic disease
Elimination of stress, treatment of concurrent disease
Tempt to eat / enteral nutrition (by stomach tube)
Glucose infusion (5% at 2ml/kg/hr)
Partial parenteral nutrition - monitor blood glucose, hourly at first, may need insulin (SC or infusion)

Question 23

What is the prognosis for horses with hyperlipaemia?

Answer 23

60-100% mortality

Question 24

How can we prevent hyperlipaemia?

Answer 24

Client education

Identify ‘at risk’s - glucose infusion and insulin if required, to avoid hyperlipaemia