Equine Endocrine

Question 1

Which layers make up the pituitary gland?

Answer 1

Pars Tuberalis
Pars Nervosa
Pars Intermedia
Pars Distalis

Question 2

Which layer of the pituitary galnd is affected by PPID in the horse?

Answer 2

Pars intermedia

Question 3

What is the Pars distalis regulated by (layer of pituitary gland)?

Answer 3

Neurotransmitters released from axons from hypothalamus

Question 4

What is the Pars nervosa regulated by (layer of pituitary gland)?

Answer 4

Neurones. Direct axonal connection with the hypothalamus

Question 5

How does PPID occur?

Answer 5

Loss of dopamine!

• Neurodegenerative lesion-loss of dopaminergic inhibition -> excess pars intermedia hormones (B-endorphins, CLIP, a-MSH, ACTH)
• Hyperplasia/adenomatous change to pars intermedia

Question 6

What age of horses are usually affected by PPID?

Answer 6

15 years or older

Question 7

What are the clinical signs of PPID?

Answer 7

Hirsutism (long hair coat) varies from delayed/abnormal shedding to thick curly coat
Laminitis (50-80%)
Sweating
PUPD
Weight loss and redistribution
Wasted epaxial muscle and pot belly
Bulging supraorbital fat
Lethargy
Susceptible to infections
Rarely CNS effects (extension to brainstem)

Question 8

How do you diagnose PPID?

Answer 8

Tier 1 tests:
-Basal ACTH (collect when horse is unstressed ie not after transport)
Dynamic endocrine tests:
-Low-dose dexamethasone suppression test (overnight)
If positive, begin tx. If inconclusive:
Repeat Tier 1 tests or do a Tier 2 test:
-ACTH response to TRH stimulation

Question 9

How do you do a low-dose dexamethasone suppression test?

Answer 9

Take baseline serum cortisol
Give 40ug/kg dexamethasone IM
Retest cortisol 20 hours later
If normal: cortisol levels should fall
If PPID: cortisol levels fall slightly then rise

Question 10

How do you do a TRH stimulation test (of ACTH)?

Answer 10

Particularly useful when horses with early PPID have normal resting ACTH
TRH causes the pituitary gland to release more hormones -> ACTH conc increases
Take a baseline serum ACTH
Inject 1mg TRH iv
Retest ACTH every 10 mins over an hour
Will get an increase in ACTH if PPID

Question 11

What is the treatment for PPID?

Answer 11

Pergolide

Starting dose: 0.002 mg/kg/day

Question 12

What should you monitor in horses with PPID to prevent them developing laminitis?

Answer 12

Insulin

Question 13

Suggest a protocol for monitoring PPID

Answer 13

Baseline diagnosis
Monthly evaluation of ACTH and insulin for 3 months and if stable, 3-monthly evaluation for 9 months
More prolonged monitoring eg every 6 months in well-managed cases

Question 14

Give some problems with high doses/increasing doses of pergolide when treating PPID

Answer 14

May cause inappetence

Laminitis/high insulin

Question 15

How do you diagnose hypothyroidism in horses?

Answer 15

TRH stimulation test (different from PPID test-measure T3 and T4 4 to 5 hours later)

Question 16

Feeding excess what can cause hypothyroidism?

Answer 16

Iodine

Question 17

What is EMS?

Answer 17

Equine metabolic syndrome

Syndrome of obesity (generalised or regional), laminitis (or predisposition), and insulin resistance/hyperinsulinaemia

Question 18

Give some factors that lead to insulin resistance in the horse

Answer 18

Obesity -> abnormal fat (fat starts acting like its own endocrine organ, releasing things it shouldn't)
-Free fatty acids
-Altered local glucocorticoids
-Myostatin
-Dysfunctional and pathogenic adipocytes
-Impaired insulin signalling
-Endothelial dysfunction
Overfeeding, certain sugary grasses (eg rye grass)

Question 19

Besides laminitis, what other hoof problems may a horse with EMS experience?

Answer 19

Frequent foot abscesses
White line disease
Lamella rings
Seedy toe
Dropped sole

Question 20

Which horse breed is more genetically prone to EMS?

Answer 20

Dartmoor ponies

Question 21

Why do horses with EMS get laminitis?

Answer 21

Prolonged hyperinsulinaemia -> damage to lamellae cells -> lose structure -> stretch and elongate -> rupture just underneath hoof wall

Question 22

How can you diagnose EMS?

Answer 22

Resting hyperinsulinaemia (>20ulU/ml)
Combined IV glucose and insulin test
In-feed sugar tests (starve for 6-12 hours, give 1/2 scoop of forage chaff with 1g glucose powder per kg BW, take blood sample 2hr later and measure insulin. If insulin is >81mlU/L -> risk of laminitis)

Question 23

What other findings may you find in horses with EMS?

Answer 23

Hypertriglyceridaemia
Mild elevation in basal cortisol
High blood pressure
Swollen sheath in males

Question 24

How does EMS differ from PPID in its presentation?

Answer 24

Ponies/horses with EMS are younger than those with PPID
No hirsutism
Negative for PPID on dynamic and basal tests

Question 25

How do you treat EMS?

Answer 25

Reduce obesity (predisposing factor)
Reduce hyperinsulinaemia
Treat and manage laminitis
Monitor response

Question 26

How much hay should a horse have a day?

Answer 26

1.5% BWT hay (fresh weight)

Question 27

How can you manage hyperinsulinaemia in horses with EMS?

Answer 27

Exercise
Diet
Drug therapy- Metformin, or Thyroxine

Question 28

Where will a horse with laminitis be sorest?

Answer 28

Toe

Question 29

What are the 4 grades of laminitis?

Answer 29

Grade 1: shifting
Grade 2: lame when walking
Grade 3: can’t pick up a hoof
Grade 4: can’t walk

Question 30

What treatment would you recommend for laminitis?

Answer 30

Bute, ice may help reduce swelling, box rest to stabilise lamellae and prevent rupture, sole support eg deep bedding, loose sand, support hoof with softban/cotton wool

Question 31

What is the normal range for blood glucose?

Answer 31

4-5 mmol/L

Question 32

What is the normal range for blood insulin?

Answer 32

22 ulU/ml

Question 33

How can you monitor a horses weight?

Answer 33

Weight tape

BCS

Question 34

What do increased globulins indicate?

Answer 34

Inflammation

Question 35

What does increased SAA (serum amyloid-A) and WBCs indicate?

Answer 35

Inflammation