Laminitis – Causes and Consequences Flashcards
(38 cards)
Why is laminitis such an important disease?
- Very common problem in First-opinion practice.
-Causes huge amount of equine suffering and welfare issues. - A considerable drain owner emotions/finance/time
- A common cause of euthanasia
- Often (badly) dealt with by owners without (enough) veterinary involvement
Define laminitis
Inflammation of the lamellae
“An acute onset lameness of variable severity involving one or more feet”
“the failure of the attachment between the distal phalanx (coffin bone) and the inner hoof wall”
Describe the anatomy of the hoof
- Underneath the horn is the dermis
- Horn produced by the coronary band
- Junction between the sensitive and insensitive tissue (area that goes wrong in laminitis)
- Lamellae = “Thin sheet”
- About 600 Primary lamellae per hoof
- About 150 Secondary lamellae per primary lamellae
Describe the anatomy of the sole and describe weight bearing in the hoof
- No lamellae on sole of foot
- Weight bearing mostly done through lamellae, frog and walls of hoof.
- So the sole isn’t designed for weight bearing
- Excessive pressure on solar corium (dermis) tissue = painful
Describe the blood supply in the hoof
Foot – very well vascularised.
Aterio-venous shunts present in laminae
Why does the foot need to be well vascularised?
Constant supply of glucose needed to keep basement membrane structures intact.
- A single horses’ hoof uses more glucose per day than its brain.
- Glucose uptake in the foot not insulin mediated.
Name some of the modern theories for laminitis
- Vascular Theory
- Endotoxaemic\sepsis\inflammatory theory
- Carbohydrate overload theory
- Supporting limb laminitis
- Mechanical laminitis
- Glucose deprivation theory
Name a real and common cause of laminitis
Endocrinopathic laminitis
Name 5 real and uncommon causes of laminitis
Endotoxic/septic/inflammatory laminitis
Mechanical laminitis
Supporting limb laminitis
Glucocorticosteroid induced laminitis
Carbohydrate overload
What is the vascular theory of laminitis
Laminitis caused by alterations in blood flow to digit – leading to tissue hypoxia, ischemia, tissue necrosis, inflammation and ultimately laminar failure
Compare the evidence for and against the vascular laminitis theory
For: Vascular changes well proven - both vasoconstriction and vasodilation
Against:
- No consistent pattern of change found
- Histopathological signs of inflammation not always present in pasture associated laminitis.
- What initiates the vascular changes?
What is the endotoxic/sepsis/inflammatory theory of laminitis
Laminitis caused by the effects of endotoxins and other inflammatory substances on the foot.
Compare the evidence for and against the endotoxic/sepsis/inflammatory theory of laminitis
For: Laminitis well recognised as a potential complication of SIRS/Endotoxemia in horses e.g. retained foetal membranes, colitis, post colic surgery, pleuropneumonia
Against:
- Not every endotoxic horse gets laminitis.
- Most laminitics not endotoxic.
- Injection of endotoxins to horses does not reliably induce laminitis
Describe the supporting limb laminitis theory
Horses which are non-weight bearing on one leg often develop laminitis in the contralateral limb
Compare the evidence for and against the supporting limb laminitis theory
For: Definitely does occur – in very severe lameness (fractures etc.)
Against:
- Limited to severe lameness: not every lame horse gets laminitis
- Not representative of pasture associated laminitis
Describe the mechanical laminitis theory
Any force which physically tears hoof from the laminae is technically laminitis.
Either occurs as a (very) traumatic one-off incident or as a result of chronic forces on an already weakened digit.
Compare the evidence for and against the mechanical theory
For: Logically can occur. Probably quite common in severe chronic laminitis
Against: Little researched evidence, mostly anecdotal, difficult to prove condition exists
Describe the glucocorticoid induced laminitis theory
Glucocorticoid administration to horses can cause laminitis.
Long held belief that glucocorticoids practically contra-indicated in horses
Compare the evidence for and against the glucocorticoid induced theory
For: Well documented evidence that this can occur - even after one-off intra-articular doses.
Against:
- Modern epidemiological studies shown risk is genuine, but actually quite low.
- Deliberately trying to induce laminitis by giving steroids (for research purposes) rarely works
- Using high doses of steroids or using them in animals already predisposed to laminitis likely to increase the risk.
- Oral prednisolone shown to be quite safe.
Describe the fructans and carbohydrate overload theory for laminitis
- Mammalian digestive tracts lack the enzymes to digest fructans therefore they spill into the large bowel intact.
- Bacteria can digest fructans.
- Fructan overload therefore implicated as the source of pasture-associated laminitis.
Fructan level in plants depends on which factors?
- Type of plant, part of plant, growing season, ambient temperature, sunlight levels, “stress” levels
- Highly variable, can change from hour-to-hour – can’t predict pasture levels.
Compare the evidence for and against the the fructans and carbohydrate overload theory for laminitis
For:
- Large quantities of oral fructans will reliably induce laminitis in experimental studies.
- Could easily explain pasture-associated laminitis
Against:
- Can horses physically consume enough fructans in a day to cause laminitis ?
Controversial – most experts consider it unlikely, although some disagree.
Describe the practical relevance of the fructans and carbohydrate overload theory for laminitis
- Carbohydrate overload is just a form of endotoxic/septic/inflammatory laminitis (since a form of colitis is induced) and does not reflect pasture-associated laminitis.
- Concept still widespread with horse owners.
- Lead to use of in-feed antibiotics to prevent hindgut fermentation
Name 3 underlying endocrinopathies that can lead to laminitis
- Equine metabolic syndrome
- Equine pars pituitary intermedia dysfunction
- EMS and PPID together
