Laminitis - equine Flashcards
What is laminitis characterised by?
failure of attachment of epidermal cells of the epidermal (insensitive) laminae to the underlying basement membrane of the dermal (sensitive) laminae
Risk factors - laminitis
- 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)
3 stages of laminitis
- DEVELOPMENTAL: contact with trigger, lasts up to 72 hours, no overt signs
- ACUTE: see CS, lasts a few days or else –> chronic
- RESOLUTION or CHRONIC: exact cascade of events and interactions b/w these processes yet to be elucidated
What are the 4 main pathogenesis categories of laminitis?
- inflammation
- ECM degradation
- metabolic disease
- endothelial and vascular dysfunction
- cascade and interactions of factors yet to be elucidated
Outline role of inflammation
- previously questioned
- systemic inflammatory response that accompanies hindgut carbohydrate overload somehow initiates lamellar inflammatory events
Outline role of ECM degradation and laminitis pathogenesis
- 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
Outline metabolic diseases in pathogenesis of laminitis
- 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
Outline vascular and endothelial dysfunction
- 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
Aims in approach to suspect case
- make definitive diagnosis
- determine underlying cause
- determine if likely to recover the expected level of soundness
Dx - laminitis
- 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
What might indicate P3 has moved? 2
- depression at coronary band
- softening of sole at point of hoof
What radiographs need to be taken for suspect laminitis?
- 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)
Which endocrine diseases might you want to r/o with laminitis?
- PPID
- EMS
Dx tests - PPID
- CS
- basal ACTH (seasonally adjusted reference range)
- Dex suppression test (not autumn)
- TRH suppression test
Dx - EMS
- Hx
- CS
- Demonstration of IR (fasting insulin and glucose, dynamic test)
T/F: once CS become apparent all of the pathological changes have already occurred in the foot
True
Aims - laminitis tx - 2
analgesia and foot support
Analgesia - laminitis
- NSAIDs (PBZ, flunixin, carprofen, iv or oral)
- Opiates (morphine, pethadine, fentanyl) in hospital as controlled drugs, short acting and side effects
Outline vasodilator therapy in laminitis
- 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
Vasodilator drug to affect equine digital blood flow
only ACP effective (NOT nitroglycerine ointment/ Percutol)
How can you cause distal limb vasoconstriction in horse?
- ice
- limb distal to carpus/ tarsus should be chilled continueously to
How can foot support be provided in laminitis cases?
- essential
- increase bedding: depth, bring to door
- Frog support: bandages, lilypads, NFS etc
- Frog and sole support: styrofoam, dental impression material etc.
Management changes - laminitis
- 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)
Tx - PPID
pergolide
= dopamine-R antagonist
- controls ACTH output
Tx - EMS
- weight loss
- increased exercise
+/- pharmacological agents
What does laminitis prognosis depend on?
- 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)
Define NSC
Non-structural carbohydrate
What is the #1 priority for pasture-associated laminitis?
Prevention and laminitis is associated with overconsumption of NSC (fructan+starch+ sugar) which provides energy for growth of plants
Outline how NSC levels fluctuate
- 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
How should pasture be managed regarding NSC?
- 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
What should you do if extra energy is needed in diet?
oil or unmollassed beet pulp can be added to diet
What should you do if cereals are fed?
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
What grazing changes should be recommend for laminitis prevention?
- 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
3 main aspects of laminitis prevention
- grazing / diet management
- regular exercise
- prevent obesity
Name 3 supplements that have been suggested to help prevent laminitis
- cinnamon
- magnesium
- chronium
How may cinnamon reduce laminitis risk?
- claimed to be insulin sensitising
- but no equine studies
- equivocal results in man and rats
How may magnesium prevent laminitis?
- possibly modulates action of insulin
- mixed results in humans with diabetes and no equine studies
- best to ensure adequate intake (10-15g/day)
How may chromium reduce laminitis risk?
- 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
