What is laminitis?
Did you know that there are three different types of laminitis? Laminitis caused by grass or founder, as it is commonly called, is inflammation of the laminae of the horse’s foot. Laminae are the delicate, accordion-like tissues that attach the inner surface of the hoof wall to the coffin bone - the bone in the foot. The sensitive laminae interlock with insensitive laminae lining the hoof, much like interlocking fingers to keep the coffin bone in place within the hoof.
What causes it and why?
Lush grass is known to present a laminitis risk. This is because it’s high in soluble carbohydrates which are simple sugars and starches that are readily broken down by the bacteria in the horse's large intestine. One of the consequences of rapid breakdown of these carbohydrates is production of a substance that, when absorbed into the bloodstream, can damage an important structure in the hoof: the basement membrane. This structure essentially forms the "glue" that attaches the hoof wall to the pedal bone, or coffin bone. Breakdown of the bond between the hoof wall and the pedal bone is the basic process that triggers the destructive chain of events associated with laminitis.
The sugar fructans produced by rapidly growing grass stimulates an overgrowth of bacteria in the horse’s large intestine. The bacteria produce and release toxins, called endotoxins, that are carried by the bloodstream to the foot where they cause damage to the laminae and small blood vessels.
Why is laminitis more common at certain times of the year?
Of the soluble carbohydrates found in grass, one of the most important is fructans. It has relatively recently been discovered that grasses not only store energy in their seed heads, they store energy in their roots, leaves and stems as fructans. In the spring, when there are sunny days followed by cool nights, the grass stores large amounts of fructans in the stems, especially the portion of the stem near the ground. Later in the year, when the daylight and night time temperatures are more consistent, most of the fructans produced by the plant during the day, is used up each night.
The fructans levels are highest in the spring and summer months. However, having said that, it’s worth mentioning that this is not the only time when laminitis occurs. Although far less common, it can happen during a mild, wet autumn or after a drought. In other words, any time rainfall, sunlight, and daytime temperatures are sufficient to stimulate rapid grass growth.
What’s the best time of the day to turn out?
On sunny days, fructans levels gradually rise during the morning, peaking around noon. They then gradually decline and are lowest just before dawn. So, the riskiest time for a laminitis-prone horse to be turned out is between late morning and late afternoon, in the spring or early summer. Avoid these times if you can.
Why do some horses get it, but others do not?
Historically, it was thought that the sole cause was access to lush pasture but this doesn’t explain why some horses develop the condition and others do not, e.g. if you put two horses together in the same field, why does one develop laminitis and the other doesn’t? Why is one susceptible to laminitis and the other isn’t? Although grass intake can be a triggering factor, it’s now understood that 90% of laminitis cases are caused by an underlying hormonal condition.
So, what horses do get it?
A 2016 study found that “cold blooded” horse types who had access to high-quality grazing or had a change of pasture were more at risk of developing laminitis. Cold blooded horses, such as our native pony types, are traditionally good doers who retain their fat during the summer months to help them survive the cold in the winter months. Native ponies also tend to be insulin resistant which increases the risk of the development of laminitis.
Other factors on the watch list include:
Horses that are over the age of 10
Those with a cresty neck.
What are the symptoms of laminitis?
The most disturbing thing about laminitis is that the initial developmental stages usually go undetected. It’s 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 recognised easily by the owner include those outlined below.
Very mild laminitis: this level of laminitis may be taken for arthritis or laziness as the horse just doesn’t move like they normally do.
Only trots when usually canters when turned out
Trots big on soft ground but short-strided on hard ground
May not bend to the inside when ridden as foot sore in front
Resists pivoting on front feet
Possibly heat in the feet
Stronger pulse on the inside of the pastern.
Moves carefully in walk
May trot but only when encouraged to do so
Shorter stride in trot
Head may bob a little in trot
Refuses to turn on front feet, may freeze when turned
Bounding pulse on the inside of the pastern.
Severe laminitis: you can’t miss this.
Refuses to move
May only walk when encouraged to do so
Steps are small, stiff and careful
Adopts classic, instantly recognisable laminitis stance with hind feet well under his tummy to keep the weight off his toes and more on his heels
How does laminitis feel for a horse?
The pain of laminitis must be similar to when we shut our fingers in the car door, but it’s worse for the horse because he has to stand with all his weight on the bruised area.
How should laminitis be treated?
If you are in any doubt, call your vet. Follow exactly the treatment plan laid out by your vet, introduce it as soon as possible to prevent any lasting damage and to alleviate any discomfort quickly.
Stable the horse on soft ground with a deep bed of shavings, cardboard or sand. The bedding needs to be able to mould into the hoof and around the frog to provide support.
What’s the best way to prevent it?
The good news is that there are some simple steps to prevent grass laminitis:
Use a good fitting muzzle
Restrict or keep horses off lush, fast growing fields until the grass has slowed in growth and produced seed heads
Avoid grazing horses on fields that have been grazed very short during the winter
Allow your horse to fill up on hay before you turn him out.