Of all the common lameness problems that affect horses and ponies, laminitis is one of the most feared by horse owners. And arguably so, as it is the second biggest killer of horses after colic.

Laminitis occurs when the sensitive, soft tissues connecting the pedal bone to the hoof wall (‘laminae’) are damaged.

Laminar failure combined with the sheer weight of a horse results in the hoof capsule displacing upwards in relation to the pedal bone (distal phalanx, P3, coffin bone).

If laminitis is left untreated it can be catastrophic.

It’s vital that risk factors are recognised, prevention strategies are put in place and subtle clinical signs are spotted early so that prompt treatment can be instigated.

Clinical Signs Of Laminitis

Laminitis is observed most commonly in the front hooves of the horse although we should never rule out hindfoot involvement.

Common clinical signs indicating acute laminitis are the signs of pain and include:

• Shifting weight from one foot to another (“paddling”)
• Lameness at the walk or trot, especially when the horse turns sharply
• Palpable heat in the hooves
• Bounding pulse in the digital arteries over the fetlock
• Decreased mobility, or a reluctance to walk with affected horses often lying down
• Pain with thumb or hoof tester pressure over the toe region of the sole
• Abnormal “sawhorse” stance, with the front hooves, placed further forward than normal so that the heels and hindlimbs carry more weight.
• Fluid accumulation and swelling (oedema) of the lower legs
• Increased heart rate and respiratory rate
• Trembling, sweating and visible distress
• Bruised soles or dropped soles with squashed heels or flat, dished hooves

Signs of chronic laminitis or founder include:

• Abnormal hoof growth- the heel region grows faster than the toe creating a boxy appearance and a change in angle of the dorsal hoof wall
• divergent hoof rings or grooves around the hoof wall, usually wider or lower at the heels than the toe region.
• a wide white line – a sign of stretched epidermal laminae
• flared lateral hoof wall
• toe cracks
• presence of a deep groove between the wall and sole
• extremely thick or thin hoof sole

Common causes of Laminitis

The exact mechanism of what causes laminitis is still unknown, however, there are many theories.

The most common precursors of laminitis include:

1. Equine Metabolic Syndrome

Research has shown us that by far the greatest predictor of laminitis is a horse or pony that is suffering from equine metabolic syndrome. 

These animals have a type of insulin dysfunction that means they struggle to metabolise sugars in their diet appropriately.

It’s incredibly important that horses with EMS are fed appropriately to prevent laminitis.

2. Equine Cushings Disease (pituitary pars intermedia dysfunction – PPID)

Older horses who suffer from PPID often suffer from laminitis.

The mechanism for this to occur is not fully understood, however, it is believed to be related to the higher-than-normal circulating cortisol levels, although research is not clear on this.

3. Secondary To Endotoxaemia

Any illness that causes severe inflammation/sepsis in the horse can potentially predispose it to laminitis.

• Colic
• Colitis
• Retained placenta
• Septicaemia
• Pleural pneumonia
• Peritonitis
• Carbohydrate/grain-overload

4. Compensatory Supporting Limb Failure

When a horse’s limb is damaged and cannot bear weight for an extended period of time, the other limbs must take over.

For some horses, this becomes too much for the structural apparatus and failure of the laminae occurs, resulting in laminitis.

Severe fractures are the most common reason we see this type of laminitis in horses.

5. Toxic Ingestion Of Black Walnut

The black walnut (Juglans nigra) plant is known to cause laminitis in horses after just a few hours of exposure.

The toxin is unknown, but we do know that shavings are toxic.

Always check to make sure what plant is used for shavings and avoid use if it contains Black Walnut.

6. Concussive Laminitis

This type of laminitis is rarely seen, however, it can occur when horses have been running at speed on a road or other very firm ground for quite some distance.

This usually occurs when horses have escaped from a paddock or barn, have given flight, and galloping long distances.

It is thought that the concussive forces alter blood flow, and cause inflammation and heat within the hoof capsule ultimately affecting the laminae.

7. Grain-overload or ingestion of soluble carbohydrates (lush[1] [2] [3] [4]  pasture)

A sudden increase in consumption of feed high in starch and low molecular weight sugar (non-structural carbohydrates or NSC) can cause a change to the gut microbiome that may result in laminitis.  These NSCs are mainly found in cereal grains and stressed pasture.

These energy-rich nutrients are usually fully digested in the small intestine, however, if eaten in excess or provided without a period of adaptation an undigested portion will spill over into the large bowel, where suitable bacteria for digestion then proliferate (Streptococcus genus).

It's also important to recognise that when pasture is stressed the fructan content of that plant will markedly increase.

Fructan is an oligosaccharide that some horses are particularly sensitive to. While fructans are usually digested in the hindgut quite well, there is an upper level (7.5g/kgLW) (Aetiology of fructan-induced laminitis; mechanism of fructan involvement, alteration of hindgut microflora and quantities required.C Pollitt[5] [6] ) when if exceeded, laminitis occurs.

The proliferation of streptococcus bacteria when digesting the spillover carbohydrates and fructans produces a large volume of lactic acid lowering the pH in the hindgut. 

This rapid decrease in pH results in many of the bacteria in the bowel dying and toxic substances known as ‘endotoxins’ being released into the bloodstream.

Decarboxylation of amino acids occurs causing an increase in vasoactive amines that can cause vasoconstriction.

Studies are still unclear whether it is the release of endotoxins or these vasoconstrictive amines that are causing damage to the laminae.

Preventing laminitis

Now that we understand the potential causes of laminitis, we can act to prevent its occurrence.

We do need to be mindful that research on the pathophysiology of laminitis is on-going and despite years of investigative work, the answers are still not clear.

With that said, we do know that horses with equine metabolic syndrome and/or Cushing's disease are more susceptible to laminitis and that diet plays a significant role in the prevention of these horses.

For that reason, it’s best to confirm whether your horse has EMS or Cushing's Disease.

This will allow you to make informed decisions:

• what diet to feed,
• when to allow access to pasture,
• when to use FOUNDERGUARD.

Please get in touch with your veterinarian for specific recommendations for testing your horse or pony for these conditions.

In general, laminitis can be prevented by:

1. Reducing consumption and/or access to non-structural carbohydrates. This includes pasture grass, hay and grains.
2. Provide access to pasture when the sugar content of the grass is lowest – 12 am to 9 am.
3. Feeding soaked hay (use a large volume of water for soaking) to leech out sugars. Remove the water and allow the hay to air dry prior to feeding.
4. Regular hoof care.
5. Exercised frequently to maintain a body condition score of 5-6.
6. Add FOUNDERGUARD to the diet during high-risk times or when transitioning a diet.

Founderguard^® - A proven preventative for feed-induced laminitis

FOUNDERGUARD is an in-feed supplement that contains Virginiamycin.

It works by reducing the number of lactate-producing bacteria that would normally exponentially multiply when there is a spillover of undigested carbohydrates or high levels of fructan in the hindgut.

By preventing this rapid fermentation of carbohydrates and subsequent production of these acid-producing bacteria FOUNDERGUARD can limit the number of vasoactive amines that are considered to cause vasoconstriction and ischaemia leading to laminitis.

FOUNDERGUARD is best fed in those situations where there is a change in diet, or when the grass is high in sugars such as during spring and autumn growth and periods of pasture stress.

About the author

Dr Leigh Davidson BVSc, BApplSc

Director at Your Vet Online