Explaining Laminitis
and Founder
Part Two
What Causes Laminitis?
Symptoms
What Causes Laminitis?
Though we have ample experience
of how laminitis affects the horse during the acute painful stage, we
know less about what causes things to go wrong in the first place. We
know that laminitis occurs following a number of distinct occurrences in
areas of the horses body often completely separate from the hooves:
• Following ingestion of large quantities of grain or fresh green
pasture (carbohydrate overload)
• Following localized or systemic infection (e.g. retained placenta,
respiratory infections)
• Following musculoskeletal problems (e.g. Rhabdomyolysis or ‘tying up’)
• Following periods of extended concussion (e.g. working on hard dry
ground for long distances without rest)
• Severe, painful injury to one limb causes laminitis in the opposite
supporting limb
• In response to an hormonal imbalance (e.g. Obesity, Equine Cushing’s
Disease)
• Following prolonged antibiotic treatment (disrupting hind gut
microflora)
• Following administration of excessive levels of corticosteroids
Disturbingly, there are a number of cases
each year for which there is no obvious cause; sometimes laminitis seems
to just ‘happen’ with no preceding occurrence or apparent risk factor to
blame. For the non mechanical causes above, we assume that the
triggering factor or factors are carried in the blood from wherever they
originate and when they arrive at the hooves, begin their path of
destruction. What we don’t know conclusively is what those triggering
factors are, whether they are different depending on the initializing
event and how they ultimately lead to the breakdown of the basement
membrane. It’s likely that there is more than just one trigger factor
involved, but singling out these substances will be the subject of
research studies for some time to come.
‘Disturbingly, there
are a number of cases each year for which there is no obvious cause;
sometimes laminitis seems to just ‘happen’’
Carbohydrate Overload
This type of laminitis is the most common, is one of the most studied,
and so is the type of laminitis that we know the most about. Recent
research has suggested a couple of pathways. Current understanding
outlines that after a large meal containing excessive levels of starch
and sugar (i.e. a large grain meal), carbohydrates that are not fully
digested in the small intestine pass back to the hindgut where they are
fermented by certain sugar loving microbes. These microbes produce
lactic acid as a by product, which in turn destroys many of the more
sensitive microbes. As the balance is disturbed and the microbes
continue to die, they release endotoxins which Dr. Chris Pollitt
believes may alter the permeability (leakiness) of the hind gut lining.
It is thought that this massive shift allows the release of one or more
of the laminitis trigger factors into the bloodstream where they travel
rapidly to the hooves and begin the process of laminitis. One of the
sugar loving bacteria has been identified as a possible trigger factor
for laminitis. During carbohydrate overload, Streptococcus bovis is the
principal bacteria responsible for the fermentation of sugars to lactic
acid. The numbers of S. bovis literally explode when sufficient
carbohydrate is introduced to the hind gut. Laboratory models of
laminitis have shown that S. bovis readily activates the MMP enzyme
imbalance and experimentally causes laminitis. If it can be shown that
S.bovis manages to escape the confines of the equine hind gut and reach
the internal structures of the foot, this may answer one of the
questions regarding trigger factors, at least for laminitis caused by
grain overload.
Grass Founder
The modus operandi of grass founder is thought to be slightly different
to grain founder, though usually leads to the same end result. In grass
founder, research has concentrated on the presence of certain
carbohydrates in grasses. In 1998 researchers Annette Longland and
Andrew Cairns from the institute of Grassland and Environmental Research
in Aberystwyth, Wales described the mechanism by which grasses store and
use sugars as their energy source. Most plants store carbohydrate as
starches (chains of the simple sugar glucose), but grasses store
carbohydrate as fructan (chains of the simple sugar fructose). Grasses
contain varying proportions of carbohydrates such as sucrose, glucose,
fructose and fructans stored from the process of photosynthesis (the
plants mechanism of making food for the energy to grow). Depending on
climate and conditions, levels of sucrose and fructans fluctuate in
grasses, and the researchers explained that variations in exposure to
sunlight, day length, temperature and soil fertility etc. would
drastically affect the levels of these carbohydrates in grass. They went
on to explain that sugars are only produced during the day whilst there
is light to power photosynthesis, and at night the plant uses the stores
accumulated during the day. This means that the lowest levels of fructan
would be present at first light, and the highest levels would be present
in the evening. Some hays cut late in the afternoon in cool but sunny
weather can contain high levels of fructan and the temperate grasses of
southern regions are deemed to be more dangerous than the tropical
species found further north.
‘…the lowest levels
of fructan are present at first light,
and the highest levels are present in the evening’
Fructans are stored in the lower part of
the plant, so when grasses have been cropped close to the ground, the
re-growth contains fructans as the primary storage unit. The more
stressed the plant is, the slower it will grow, and the higher the
concentration of fructans will become. For example, grasses that are
exposed to stressful conditions such as frost will still produce fructan,
but growth will be limited, so the fructan will be concentrated in the
short grass. In Australia, where severe droughts are commonplace, the
re-growth following drought breaking rain can contain dangerous levels
of fructan. So in any of these conditions, a horse could be eating a
diet that is very high in fructan – but what does this mean? Grass
laminitis is a seasonal problem in most cases, brought on by the fresh
growth of spring grass that is high in total sugar content (and
presumably fructan). But laminitis has also been seen in horses that are
restricted to ‘starvation paddocks’, where the short grass is stressed
but still rich in fructans. Fructan cannot be digested in the small
intestine, so passes through straight to the hind-gut.
‘In Australia, the
re-growth following drought breaking rain
can contain dangerous levels of fructan’
Rapid consumption of these sugar rich
grasses is thought to overwhelm the hind gut with fructan and other
carbohydrates that escape digestion in the small intestine, similar to
grain overload. But there, it is thought that the similarity ends. It
has always been difficult for researchers to explain why the
developmental stage of laminitis is not seen in grass foundered horses
as it is in grain overload, with the horse or pony being discovered in
severe pain, with no preceding signs. Perhaps the differences are a
result of a difference in the way that fructans are fermented, and the
way in which the trigger factor is released. Perhaps in the case of
grass founder, the trigger factor is altogether different to that of
grain overload, as yet, we just don’t know. This is the area of
laminitis research currently being studied by Dr. Chris Pollitt New
research could lead to the development of an analysis kit to assess the
risk of certain pasture types and to indications about the best time of
day for turnout in susceptible horses. It has already been accepted as
common practice to limit turnout in susceptible horses during the day in
the growing season, to beware of grazing stressed pastures and that
feeding lucerne hay may be a good alternative as lucerne is relatively
low in carbohydrates and fructan. We may in the future see special
‘laminitis proof’ pasture’s being developed with cultivars of grasses
designed to have a low fructan content, but for now, we must observe the
suggestions based on the facts that we have so far.
Concussion Laminitis
Though the feet of our equine friends are strong, they were never
designed to take the kind of forces that we regularly thrust upon them.
During the long hot summers, when the ground becomes extremely
compacted, there is an increased risk of concussion laminitis. Pounding
away on hard ground day after day affects the blood flow to the foot and
may cause changes in the lamellar membrane. This in turn may lead to the
mechanical tearing of the lamellar membrane leading to the partial or
total breakdown of attachment to the pedal bone as previously described.
This type of laminitis may affect only a portion of the lamellar
surface, and so may not lead to a complete breakdown of the membrane,
but can nevertheless be devastating for the horse involved.
Symptoms of Laminitis
The most disturbing thing about laminitis is that the initial
developmental stages usually go undetected. It is only once the horse
has begun to feel the pain of laminitis that the owner recognizes that
something is amiss. Of course, by the time the pain is evident, much of
the damage has already occurred, and the onus is then on damage control.
Some of the symptoms currently recognized easily by the owner include:
• In the early stages, restlessness,
warmth in the feet, shifting of weight from one foot to the other – if
you notice these signs after a high risk incident, or your horse has had
laminitis previously, it is wise to seek veterinary help immediately.
Once the condition has become acute:
• Sore feet, usually in the front, but can also be apparent in the rear,
especially in donkeys. The toe region is especially sensitive when
tested with hoof testers.
• Throbbing digital pulse and heat in the feet
• Short, choppy strides and/or general reluctance to move, lameness in
one or more limbs, especially when turning circles
• Characteristic ‘rocking horse’ stance with the hind legs tucked well
under the body and the forelegs stretched out to allow weight transfer
to the heel region.
• Bruising on the sole as a result of pedal rotation or sinking crushing
the underlying capillaries, and bruising of the white line area
In chronic ongoing laminitis cases:
• Rings and ridges in the hoof wall
• Bruised soles or stone bruises
• Seedy toe (widening of the white line)
• Dropped soles
As we begin to learn more about
laminitis, it is hoped that we will be able to pick up on some other
early warning systems that can be recognized by the horse owner and used
to begin treatment more rapidly.
Article reproduced
courtesy of
Kentucky Equine Research
Part One
Introduction
Anatomy of the Horses Foot
What Happens When a Horse Suffers a Laminitis Attack?
Part Three
Diagnosis
Current Advice on Treating Laminitis
Prevention
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