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Equine
Laminitis
By Dr by C. Pollitt
RIRDC
Chapter 1: What is Laminitis?
Introduction
In the normal horse or pony the distal phalanx
(coffin or pedal bone) is attached to the inside
of the hoof by a tough, but flexible, suspensory
apparatus. The surface of the inner hoof wall
is folded into leaf-like lamellae (laminae)
to increase the surface area of this suspensory
apparatus. A horse has laminitis when these
lamellae suddenly fail. Without the distal phalanx
properly attached to the inside of the hoof,
the weight of the horse and the forces of locomotion
drive the bone down into the hoof capsule. Important
arteries and veins are sheared and crushed and
the corium of the coronet and sole is damaged.
There is unrelenting pain in the feet and a
characteristic lameness.
Laminitis
The Problem of Laminitis
Laminitis is the most serious disease of the
equine foot and causes pathological changes
in anatomy that lead to long lasting, crippling
changes in function (chronic laminitis or founder).
It is the second biggest killer of horses after
colic. In the USA National Animal Health Monitoring
System (NAHMS) report of the year 2000, 13%
of all horse establishments (excluding racetracks)
had a horse with laminitis in the previous year
and 4.7% of these died or were euthanased.
Laminitis has a developmental phase during
which lamellar separation is triggered.
This precedes the appearance of the foot pain
of laminitis. The developmental period lasts
40 - 48 h in the case of laminitis caused by
excessive ingestion of soluble, non-structural
carbohydrates, such as starch or fructan. Sometimes
no developmental phase can be recognized; the
horse or pony is discovered in the acute phase
of laminitis with no apparent ill health or
inciting problem occurring beforehand. This
appears to be the case with grass founder (laminitis
resulting from the ingestion of lush pasture).
Many people own and care for horses all their
lives and never encounter a horse with laminitis.
However, when it does strike, laminitis can
be heartbreaking. The pain and suffering are
relentless and sometimes, euthanasia is the
only responsible option for an owner, despite
the stoic ability of many horses to live on
as cripples. Formulating an effective management
plan for a horse with laminitis is one of the
most difficult tasks a horse owner can be confronted
with. The owner, in consultation with a veterinary
clinician and farrier, will have to decide if
the investment of money, time and energy is
worthwhile. After months of treatment and the
expenditure of perhaps thousands of dollars,
the horse in question may still be suffering
severely. The clinical signs, the extent and
severity of lamellar pathology and the response
to therapy vary unpredictably between individual
horses and this makes a rational treatment strategy,
with an accurate prognosis, difficult to formulate.
Severe damage to the internal anatomy of the
hoof can occur within the space of a few hours
and the severity and extent of this initial
damage is the single most important factor influencing
the final outcome.
Laminitis Research
Scientific understanding of laminitis is incomplete
and the horse owner often becomes committed
to the symptomatic treatment of a chronic condition
that inexorably deteriorates. This lack of understanding
of the processes involved is frustrating to
the horse owner and veterinarian alike, and
of little use to the horse. Over the last six
years, the RIRDC horse programme has made understanding
laminitis and seeking improved treatment strategies
a priority. This report is the result of six
years continuous RIRDC funding to the Australian
Equine Laminitis Research Unit (AELRU) based
in the School of Veterinary Science at The University
of Queensland. It describes laminitis in the
most up to date way possible, although there
are still large gaps in our knowledge. To understand
what goes wrong with an organ, it is essential
to first learn about its normal structure and
function. Thus, the first part of this publication
details what is already known about lamellar
anatomy and presents the results of research
carried out at the AELRU on the structure and
function of the normal horse’s foot. This
is followed by a description of the developmental
mechanism of laminitis that has been elucidated
from our findings.
Finally, a review of first aid measures for
the foundering horse is presented and ways and
means of rehabilitation.
The hope is that a better understanding of
laminitis will lead to a more unified approach
and rational treatment, by owners, veterinarians
and farriers alike.
Key Points
• Laminitis is caused by failure of the
attachment of the distal phalanx to the lamellae
on the inside of the hoof.
• The disease causes pathological changes
in hoof anatomy that cause crippling pain and
a characteristic lameness.
• Specialist intervention is required
in the treatment of laminitis, but the response
to therapy can be unpredictable.
• Research that paves the way to a better
understanding of laminitis may lead to more
successful treatment of horses suffering from
the disease.
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Chapter 11: Prognosis and Future Directions
Some horses that show the clinical signs of
acute laminitis recover completely if treated
promptly using a combination of rational medical
therapy and mechanical support.
However, horses recovering from even the mildest
laminitis should be rested and observed closely.
If no radiographic evidence of palmar displacement
of the distal phalanx within the hoof capsule
exists, and the digital pulse is not palpably
exaggerated 48 hours after treatment has ceased,
the horse can be cautiously returned to its
usual function.
If radiographs do show displacement of the
distal phalanx, then the prognosis must be more
guarded. Horses with a mild increase in the
distance between the distal phalanx and the
dorsal hoof wall, with or without rotation of
the distal phalanx, often make an apparent recovery
and remain sound indefinitely. However, horses
with marginally greater displacement and rotation
of the distal phalanx make only partial recoveries
and often have a history of intermittent lameness,
especially after exercise. Histopathology of
the hoof lamellae of partially recovered horses
shows a reduction in the number of secondary
epidermal lamellae. Many of the SELs had distorted,
abnormal shapes even several years after the
initial episode of laminitis. Some SELs become
isolated from their attachment to the PEL and
exist as isolated, unattached islands adrift
in the lamellar connective tissue (Figure 11.1
and Figure 11.2). If the surface area of the
lamellae of the inner hoof wall is reduced after
laminitis, the effectiveness of the lamellar
distal phalanx suspensory mechanism must also
be reduced. In other words, horses developing
laminitis associated with significant initial
lamellar destruction, as manifest by radiographic
displacement of the distal phalanx, appear never
to make a complete anatomical recovery and are
prone to recurrent episodes of foot pain.
Ultimately, the prognosis is directly proportional
to the severity and extent of lamellar pathology.
Horses with more than 15 degrees of rotation,
accompanied by downward displacement of the
distal phalanx into the hoof capsule within
4-6 weeks of the initial episode of laminitis,
have a poor prognosis. Prolapse of the distal
phalanx through an already necrotic sole, accompanied
by subsolar and sublamellar infection, usually
occurs.
Pus will discharge from the coronet and the
heels. Osteomyelitis and lysis of the distal
margin of the distal phalanx will develop. Such
cases will require months of expensive supportive
care and surgery and although the occasional
horse does make a surprisingly good recovery,
most suffer months of crippling foot pain and
recumbency, and eventually require euthanasia
on humane grounds.
Outcomes
The road to recovery after a serious bout of
laminitis is a rocky one. The extent of the
lamellar pathology lies hidden beneath the hoof
wall and we can only guess at what is really
going on. Radiographs and the initial degree
of pain expressed by the horse (often masked
by pain-killers such as phenylbutazone) give
valuable clues. Rapid sinking of the distal
phalanx into the hoof capsule and involvement
of all four feet make recovery unlikely.
If the horse is clearly more mobile and comfortable
after shoeing, this is a sign that the chosen
therapeutic technique is working. Over time,
the red, necrotic solar corium, beneath the
displaced tip of the distal phalanx, will re-epithelialise;
turning light yellow in colour as new horn cells
colonise the damaged area. The reappearance
of thick, concave sole is an encouraging development.
A return of hoof growth parallel to the coronary
band especially at the front of the foot is
also encouraging. Many horses recover to be
sound enough for breeding purposes or paddock
retirement. They will however require prolonged
aftercare in the form of frequent expert shoeing
and perhaps confinement to a personal yard.
A few return to former athletic soundness.
Future Directions
At the AELRU the search for the fundamental
causes of laminitis continues. Using advanced
biochemical and molecular biological techniques
we plan to thoroughly investigate the link between
bacterial overgrowth in the horse’s bowel
(particularly that induced by the key pasture
carbohydrate fructan) and events occurring at
the basement membrane of the hoof lamellae.
The real hope for horses as they confront their
crippling adversary, laminitis, is a means to
effectively prevent it. Once the devastating
pathological cascade of laminitis is underway,
the anatomical dislocations are so overwhelming
that there is little hope that mankind will
develop technology to be able restore a foundered
foot to normal. When the reason behind the failure
of a normally robust, trouble-free attachment
apparatus between hoof and bone are understood,
the way will be clear to develop effective preventive
strategies.
Key Points
• Recovery from laminitis is unpredictable,
but generally the prognosis is directly proportional
to the extent of displacement of the distal
phalanx and the resultant lamellar pathology
that occurs.
• The return to a normal-looking hoof
takes time and prolonged aftercare will often
be required. Few horses return to their former
athletic soundness after chronic laminitis.
• Research at the AELRU is devoted to
discovering the mechanism by which the basement
membrane and lamellae separate, because prevention
of this terrible disease represents a better
option than trying to repair the gross anatomical
dislocations once they have occurred.
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