Laminitis

Laminitis is a disease of the feet of hoofed animals (‘ungulates’), most commonly affecting horses and cattle. Classic signs in horses suffering from laminitis are lameness and heat around the affected hoof. The disease is one of the most common causes of lameness and can even be fatal The condition is primarily an inflammation of the digital laminae of the hoof, for which there are a number of causes.

In order to protect against laminitis owners must make themselves aware of the causes and symptoms associated with its early stages. Early diagnosis is critical in getting a full recovery.

What is Laminitis?

Laminitis is Inflammation of the digital laminae of the hoof that supply and contains a network of capillaries and nerves that together act to nourish and secure the coffin bone to the hoof wall. As all of the horse’s weight is resting on these four hooves, which are also acting as shock absorbers during locomotion, the blood supply must be optimal in order to maintain fitness. When the blood supply to laminae is compromised due to this inflammation, the laminae can become progressively detached from the coffin bone causing sinking and/or rotation of the bone within the hoof.

What causes Laminitis?

The possible causes of Laminitis are extensive, and relatively poorly understood. Broadly speaking they can be split into either mechanical or systemic causes. Mechanical causes would include any injury associated with an external element, whilst systemic causes are associated with nutrition, blood supply, or other internal factors.

Mechanical Laminitis

Mechanical laminitis occurs when the hoof wall is pulled away from the bone or lost entirely through excessive or persistent trauma. External injuries that damage the hoof wall significantly enough to affect the underlying digital laminae are also known causes, but are rare.

Systemic laminitis

Systemic laminitis usually affects two feet, and although it can affect all 4 feet it typically affects the front feet. Systemic Laminitis can lead to rotation or sinking of the coffin bone placing undue pressure within the hoof capsule, leading to abscesses which can be severe, very painful, and difficult to treat.

Currently there are three main hypotheses for mechanisms that may result in laminar failure.

Classical inflammation: This includes infiltration of potentially destructive white blood cells. It is suggested that this is caused by a carbohydrate overload, either by an excessive grain intake or pasture that is under stress and has excessive sugars in it. The horse may be unable to digest all these carbs in the foregut, moving into the hindgut and fermenting in the cecum. This results in endotoxins being absorbed into the blood stream and which leads to whole body inflammations. In the feet this can lead to damage to other tissues as there is no expansion space for inflamed tissues and laminitis resulting. An example of such would be laminitis following colic, or a retained placenta in a mare after foaling.
Ischemia-reperfusion injury: This is injury to tissue at a cellular level caused by a loss of blood supply and oxygen followed by an influx of blood and oxygen. Researchers have seen both decreased and increased blood flow to the laminae in laminitis cases and as ischemia-reperfusion injury includes both, it has been widely researched as a cause for laminitis. It is still unclear what the trigger factors are for ischemia-reperfusion injury in laminitics.
Equine Metabolic Syndrome: The result of a long term lifestyle of being overweight which changes the way the metabolism handles glucose and insulin. This in turn leads an increased risk of becoming insulin resistant. Insulin resistance prevents glucose being taken up by the lamellae and they become weak, and prone to collapse or detachment. Horses with EMS are more likely to be prone to laminitis as a result of lush spring grass or frozen grass due to the higher concentrations of fructans.

How will your vet diagnose Laminitis?

Treating the condition effectively is dependent on getting an early diagnosis. External physical symptoms are not very specific and can be attributed to other possible issues. Veterinary examination may be enough to diagnose the condition but radiographs are a useful diagnostic tool in ascertaining the severity of the disease.

Signs

In horses where just the front feet are affected the horse will adopt the classic "founder stance": the horse will bring its hind legs underneath its body to take the weight off the front legs and put its forelegs out in front, called "pointing".
In horses where all 4 feet are affected the horse will often shift weight from foot to foot trying to relieve the pressure
Increased temperature of the wall, sole and/or coronary band of the foot.
A pounding pulse in the digital palmar artery. (The pulse is faint to undetectable in a rested horse, but is clear after hard exercise.)
Anxiety
Visible trembling
Increased vital signs and body temperature
Sweating
Flared Nostrils
Walking very gingerly, as if on egg shells
Lameness, and an unwillingness to move at all
Tendency to lie down and if severe, to remain lying down.

Radiography

A radiograph can give useful information concerning the severity of the condition including degree of rotation, sole thickness, measurement of the dorsal hoof wall thickness, and vertical deviation.

What Treatments are available?

Clear distinctions must be drawn between acute and chronic laminitis cases, as their treatment and management needs will differ. Please discuss with the practice if you have any concerns about your horse or pony.

How can I prevent my pony getting Laminitis?

Prevent carbohydrate overloads – keep feed rooms locked, keep pastures grazed tightly, or split fields into smaller paddocks
Don’t allow young stock to become overweight as this will increase the risk of the pony developing insulin resistance with consequences later in life.
Body condition score your horse every two weeks. Horses tend to gain weight in the summer and lose it in the winter. With rugs, stabling, supplementary grain and forage, feeding horses rarely lose condition in the winter time, but still gain weight in the spring. Your horses’ body condition score through the spring and summer should be ~4-5, in winter ~3-4. Further information can be found at http://www.saracenhorsefeeds.com/condition-score
Ensure he/she has plenty of forage. If you need to reduce his calorie intake don’t reduce the quantity of forage, simply soak it for 12hours which will leech out the sugars and reduce the calorie content.
In brood mares especially ensure that the diet is balanced in terms of vitamins and minerals. Suboptimal nutrition in mares has been shown to increase the risk of insulin resistance in foals.
Manage grass intake by either:
1. Fitting a grazing muzzle. This not only reduces the quantity that is consumed but it has also been shown that ponies with grazing muzzles will walk up to 5 times further during turnout than non-muzzled ponies.
2. Grazing with more horses or ruminants.
3. Reduce paddock size.
4. Top fields once/week.
5. Turnout in a sand school with soaked haynets (in the chronically obese where all the above strategies have been exhausted or are unfeasible).
Provide the horse with daily exercise to raise the HR (80bpm in active walk) for a minimum of 30 minutes
Remember that only horses that are working need additional bucket feeding. Horses or ponies that do not break a sweat when ridden should not require additional bucket feeding.
Overweight horses are a welfare concern just as much as thin horses.

References

Parker, S, 2013, Laminitis & Founder. Available at www.parkerfarrierservice.com/laminitis_founder Date accessed 01-07-2013
RVC, 2013, Research News, available at: http://www.rvc.ac.uk/Research/News/Laminitis.cfm. Date accessed 01-07-2013
Pollitt, C et al, 2003, "Equine Laminitis" (PDF). Proceedings of the AAEP 49 at http://www.ivis.org/proceedings/AAEP/2003/pollitt/IVIS.pdf Date accessed 02-07-2013
McAllister et al, 1993, Comparison of Adverse Effects of Phenylbutazone, flunixin megalumine, and ketoprofen in horses, JAVMA, 202 (1).
Doucet, M, et al, 2008, Comparison of efficacy and safety of paste formulations of firocoxib and phenylbutazone in horses with naturally occurring osteoarthritis, JAVMA, 232(1)