Laminitis - equine

Question 1

What is laminitis characterised by?

Answer 1

failure of attachment of epidermal cells of the epidermal (insensitive) laminae to the underlying basement membrane of the dermal (sensitive) laminae

Question 2

Risk factors - laminitis

Answer 2

• sepsis and systemic inflammation (GIT disease, pneumonia, septic metritis)
• endocrine diseases (PPID and EMS)
• Mechanical overload (if one severely lame non weight-bearing limb, weight transferred to another)
• access to pasture
• pony > horses
• spring and summer
• female
• increasing age
• obesity
• recent increase in body weight
• recent new access to grass
• increased time since worming (but not directly related to parturition)
• insulin resistance (IR)

Question 3

3 stages of laminitis

Answer 3

1. DEVELOPMENTAL: contact with trigger, lasts up to 72 hours, no overt signs
2. ACUTE: see CS, lasts a few days or else –> chronic
3. RESOLUTION or CHRONIC: exact cascade of events and interactions b/w these processes yet to be elucidated

Question 4

What are the 4 main pathogenesis categories of laminitis?

Answer 4

• inflammation
• ECM degradation
• metabolic disease
• endothelial and vascular dysfunction
• cascade and interactions of factors yet to be elucidated

Question 5

Outline role of inflammation

Answer 5

• previously questioned
• systemic inflammatory response that accompanies hindgut carbohydrate overload somehow initiates lamellar inflammatory events

Question 6

Outline role of ECM degradation and laminitis pathogenesis

Answer 6

• MMP activation does occur, not an initiating event
• laminar separation may occur following a failure of epithelial adhesion molecules (hemidesmosomes)
• dysregulation of cell adhesion most likely caused by inflammatory and/or hypoxic cellular injury

Question 7

Outline metabolic diseases in pathogenesis of laminitis

Answer 7

• greatest risk have metabolic phenotype (obesity and IR)
• similar to human metabolic syndrome (HMS)
• summer pasture appears to produce metabolic responses in laminitis prone ponies leading to expression of this at risk metabolic phenotype
• strong positive relationship b/w pasture NSC content and circulating insulin concentrations
• increased CHO consumption exacerbates IR In horses
• feeding a fructan-type CHO produces an exaggerated insulin response in laminitis prone ponies

Question 8

Outline vascular and endothelial dysfunction

Answer 8

• digital venoconstriction (early)
• consequent laminar oedema (early)
• venoconstriction d/t platelet activation and platelet-neutrophil activation –> release of vasoactive mediator 5-HT
• amines from hindgut fermentation of CHO are vasoactive
• IR in other spp alters endothelial function (proinflammatory condition, platelet and leukocyte activation, increased ET1 and production of mediators of inflammation and oxdant stress)
• digital vascular haemodynamic alterations (d/t inflammation, platelet activiation, action of vasoactive amines from GIT) –> lamellar injury

Question 9

Aims in approach to suspect case

Answer 9

• make definitive diagnosis
• determine underlying cause
• determine if likely to recover the expected level of soundness

Question 10

Dx - laminitis

Answer 10

• CS (lameness affecting 2+ limbs, characteristic stance of leaning back on heels, bounding digital pulses, increased hoof wall temperature, pain on hoof tester pressure at point of frog, palpable depression of coronary band)
  +/- radiography (1st presentation - if concerned P3 moved, later - if CS not improving)
  +/- enodcrine tests

Question 11

What might indicate P3 has moved? 2

Answer 11

• depression at coronary band

- softening of sole at point of hoof

Question 12

What radiographs need to be taken for suspect laminitis?

Answer 12

• lateromedial
• ensure good foot preparation
• put markers on feet (one on dorsal hoof wall starting at coronary band and one at point of bone)
• assess pedal bone rotation and founder distance (sinking)

Question 13

Which endocrine diseases might you want to r/o with laminitis?

Answer 13

• PPID

- EMS

Question 14

Dx tests - PPID

Answer 14

• CS
• basal ACTH (seasonally adjusted reference range)
• Dex suppression test (not autumn)
• TRH suppression test

Question 15

Dx - EMS

Answer 15

• Hx
• CS
• Demonstration of IR (fasting insulin and glucose, dynamic test)

Question 16

T/F: once CS become apparent all of the pathological changes have already occurred in the foot

Answer 16

True

Question 17

Aims - laminitis tx - 2

Answer 17

analgesia and foot support

Question 18

Analgesia - laminitis

Answer 18

• NSAIDs (PBZ, flunixin, carprofen, iv or oral)

- Opiates (morphine, pethadine, fentanyl) in hospital as controlled drugs, short acting and side effects

Question 19

Outline vasodilator therapy in laminitis

Answer 19

• controversial: d/t conflicting evidence as to whether the blood supply to foot is increased o rdecreased during developmental phase
• onc eCS occur, this will have passed

Question 20

Vasodilator drug to affect equine digital blood flow

Answer 20

only ACP effective (NOT nitroglycerine ointment/ Percutol)

Question 21

How can you cause distal limb vasoconstriction in horse?

Answer 21

• ice

- limb distal to carpus/ tarsus should be chilled continueously to

Question 22

How can foot support be provided in laminitis cases?

Answer 22

• essential
• increase bedding: depth, bring to door
• Frog support: bandages, lilypads, NFS etc
• Frog and sole support: styrofoam, dental impression material etc.

Question 23

Management changes - laminitis

Answer 23

• bx rest
• change diet: no grass, 1.5-2% bodyweight poor quality hay, no or minimal concentrates (HiFi = a chaff, or unmollassed sugar beet = fibre, only)

Question 24

Tx - PPID

Answer 24

pergolide
= dopamine-R antagonist
- controls ACTH output

Question 25

Tx - EMS

Answer 25

- weight loss - increased exercise +/- pharmacological agents

Question 26

What does laminitis prognosis depend on?

Answer 26

- CS - if there is a depression which extends all the way round the coronary bank suggests SINKER = 20 % survival - evidence of previous attacks = success rate decreased by 20% - RADIOGRAPHIC CHANGES: o rotation > 11.5 degrees = significantly reduced prognosis o Founder >15mm 40% chance of returning to soundness * overall one study found 95% survival after 8 weeks - lower BWt, optimal BCS and mild laminitis (Obel grade 1 and 2) were significantly associated with survival - trend towards ACP tx with survival - 72% sound at trot (significantly more likely in small horses) - 59% being ridden again (significantly more likely if no previous hx of laminitis)

Question 27

Define NSC

Answer 27

Non-structural carbohydrate

Question 28

What is the #1 priority for pasture-associated laminitis?

Answer 28

Prevention and laminitis is associated with overconsumption of NSC (fructan+starch+ sugar) which provides energy for growth of plants

Question 29

Outline how NSC levels fluctuate

Answer 29

- decreases when plant growing - increases when plant photosynthesising (high light intensity, low temperature, lack of water) - season (low early spring, greater late spring) - hay content depends on content of grass at cutting - NSC of haylage generally low but more palatable * AIM = minimise NSC intake

Question 30

How should pasture be managed regarding NSC?

Answer 30

- encourage growth (use fertiliser, regularly topped) as this lowers NSC content - hay should ideally be made from mature crop post seed dispersal (lower NSC content) - ideally want NSC

Question 31

What should you do if extra energy is needed in diet?

Answer 31

oil or unmollassed beet pulp can be added to diet

Question 32

What should you do if cereals are fed?

Answer 32

ensure they are cooked as it makes starch easier to digest in SI and feel small cereal meals to avoid getting into LI and becoming fermented. will need to add a general vitamin and mineral supplement as these will be lacking

Question 33

What grazing changes should be recommend for laminitis prevention?

Answer 33

- consider zero graxing - turn out late night to early am (low NSC) - restrict in spring and autumn (growing) - avoid if frost with bright sunshine or drought - rotate paddocks to keep grass at appropriate height - restrict intake: muzzle, strip grazing

Question 34

3 main aspects of laminitis prevention

Answer 34

- grazing / diet management - regular exercise - prevent obesity

Question 35

Name 3 supplements that have been suggested to help prevent laminitis

Answer 35

- cinnamon - magnesium - chronium

Question 36

How may cinnamon reduce laminitis risk?

Answer 36

- claimed to be insulin sensitising - but no equine studies - equivocal results in man and rats

Question 37

How may magnesium prevent laminitis?

Answer 37

- possibly modulates action of insulin - mixed results in humans with diabetes and no equine studies - best to ensure adequate intake (10-15g/day)

Question 38

How may chromium reduce laminitis risk?

Answer 38

- thought to potentiate insulin action - suboptimal intake appears to contribute to type 2 DM in man - further studies need to fully document beneficial effect in horses