Laminitis - Causes + consequences

Question 1

What is laminitis?

Answer 1

• Inflammation of the lamellae causing lameness

Question 2

Where does the horn grown from?

Answer 2

• From the coronary band

Question 3

What is the anatomy of the sole of the hoof?

Answer 3

• No lamellae on sole
• Weight bearing on lamellae, frog + walls of hoof - not sole

Question 4

What is the blood supply of the foot? (GLucose)

Answer 4

• V well vascularised - single hoof uses more glucose per day than its brain
• Glucose uptake not insulin mediated
• Glucose needed to keep basement membrane structures intact

Question 5

What are different theories of laminitis?

Answer 5

1. Endotoxemic\sepsis\inflammatory theory
2. Carbohydrate overload theory
3. Supporting limb laminitis
4. Mechanical laminitis
5. Corticosteroid induced laminitis
6. Endocrinopathic laminitis

Question 6

What is the theory of endotoxin causing laminitis?

Answer 6

• Laminitis recognised as complication of SIRS / endotoxaemia in horses
  e.g. - RFM, colitis, post colic surgery, pleuropneumonia
• Relevance = hospitalised horses

Question 7

What is the supporting limb laminitis?

Answer 7

• Horses non-weight bearing in one limb will often develop laminitis in the contralateral limb - due to failure of circulation + tissue ischaemia
• Relevance = hospitalised horses

Question 8

What is mechanical laminitis?

Answer 8

• Any force that tears hoof from laminae
• V traumatic one off or chronic forces on weakened digit

Question 9

What is glucocorticoid induced laminitis?

Answer 9

• Glucocorticoid administration can cause laminitis
• Relevance = owners should know there is a risk with corticosteroid use

Question 10

What is carbohydrate overload laminitis?

Answer 10

• Excessive carbs = overwhelms SI + overspills into large bowel = bacterial proliferation causes acidosis causing release of variety of laminitis inducing substances

Question 11

What sugars used by plants do horses struggle to digest leading to overspill to large bowel + causing bacterial proliferation + laminitis?

Answer 11

• Fructans - mammals lack enzymes to digest it = bacteria feast on the sugars

Question 12

What is endocrine induced laminitis?

Answer 12

• 90% of laminitis have underlying endocrinopathy =
  -equine metabolic syndrome (EMS)
  -pituitary pars intermedia dysfunction (PPID)
  -EMS + PPID together
• Changes of horse having laminitis if it doesn’t have EMS or PPID is low

Question 13

What is equine metabolic syndrome?

Answer 13

• Syndrome obesity, insulin dysregulation and laminitis.
• Thrifty” genotype leading to “survivor” phenotype enabling horses to survive in harsh conditions by putting on weight in good times to prepare for hard times.
• UK horses never experience “hard times” and so just get fatter and fatter…
• Lack of recognition of obesity in horse owners.
• Recent social trend to treat horses as “toys” causes welfare problems.
• Hyperinsulinaemia = cause of EMS related laminitis

Question 14

How does hyperinsulinaemia cause laminitis?

Answer 14

• Damages cytoskeleton of laminar cells and also has vasoactive properties

Question 15

How does PPID cause laminitis?

Answer 15

• Believed to be related it insulin dysregulation
• Older horses (>15y/o) - v common

Question 16

What are consequences of laminar failure?

Answer 16

• Pedal bone is free to move within the foot

Question 17

What is capsular rotation?

Answer 17

• Hoof capsule diverges from the dorsal surface of P3, but P3 itself still aligned with P2

Question 18

What is bony rotation?

Answer 18

• The hoof capsule diverges form the dorsal surface of P3, and P3 itself is rotated palmarly around the DIP. Implies significant pull of DDF and usually a sign of severe damage

Question 19

What are consequences of pedal bone movement?

Answer 19

• acute stage – gap forms where the bone was + becomes a haematoma/seroma /necrotic mess.
• If this gets infected a foot abscess will result.
• The forces on the foot stretch the white line junction – providing an easy ingress route for abscess –causing bacteria
• haematoma replaced by poor quality horn = lamellar wedge
• Rotation of pedal bone drags coronary band with it = crushed blood supply to coronary band
• Abnormal horn growth = diverging hoof rings
• Hoof remodels itself around new position of pedal bone = abnormal hoof shape = chronic lameness