Equine - Laminitis

 

PREVALENCE

Laminitis is a disease involving inflammation of the blood vessels within the equine foot. This inflammation damages the "laminae", which are the soft tissue connections between the pedal bone and the inside of the hard hoof wall, sometimes resulting in separation of the two structures.

More often found in overweight ponies and donkeys rather than horses, laminitis is a very common cause of lameness and debility. A seasonal increase in cases is seen, related to spring pasture flushes, increased concentrate feeding and the stress associated with the summer showing season. Non-seasonal cases may be related to excessive fertiliser use and/or adverse weather changes.

Initiating factors include:

•Obese, unfit animals

•Grain engorgement/access to lush pasture

•Hormonal (endocrine) Factors – Equine Cushing's Disease (more correctly called Pituitary Pars Intermedia Dysfunction/PPID) and Equine Metabolic Syndrome (EMS)

•Poor hoof conformation or inadequate farriery (long toes in particular)

•Endotoxaemia – any systemic disease involving a septic focus: e.g. retained placenta, metritis, mastitis; acute gastrointestinal disease: e.g. diarrhoea, colitis, colic

•Corticosteroid therapy

•Stress, e.g. transport

•Trauma/Mechanical e.g. repeated concussion, excessive weight bearing on contralateral limb to injured one or following limb surgery

CLINICAL SIGNS

Classically divided into acute, refractory and chronic stages - each case of laminitis is unique and the clinical manifestation of the problem is not as clearly defined as these categories. The severity of the clinical signs ranges from a relatively mild lameness through to a patient that cannot walk. Animals with acute laminitis may present with the problem in all four feet, or one or both front hooves. They typically adopt a stance with the forelimbs stretched out in front, the hindlimbs placed below the body and their weight back rocked back.　They will frequently shift their weight when standing, so as to alleviate pain at the toes.　When walking, foot placement is altered, with the heel placed on the ground before the toe. If systemic disease is the cause of laminitis, clinical signs associated with this may be present. These could include fever, increased heart or respiratory rate and inappetance. The affected feet may have a warm hoof wall and a bounding digital pulse. The patient may be sensitive to hoof testers, especially over the toe or just in front of the frog.

In long standing laminitic cases, the hooves become deformed and ridges may develop, reflecting temporary alterations in hoof growth. The sole may become flattened or convex and bruising in the toe region (associated with the tip of the pedal bone) is common. Widening of the white line and separation of the sole/wall junction related to pedal bone rotation can also occur.

Laminitis can be fatal if the pedal bone is so unstable that its supporting structures fail completely and the bone penetrates the sole of the foot.　 Euthanasia is often recommended for these sad cases on welfare grounds.


TREATMENT

Acute laminitic cases should be considered an emergency. Since each is unique, a standard treatment protocol is not applicable. A combination of the following will be utilised:

•Box rest

◦On deep, soft bedding (ideally a shavings bed). This should cover the whole surface of the floor, so the patient is completely prevented from standing on a hard surface

•Mucking out should be done around the animal, so it does not need to move from the stable

•Medications

•Anti-inflammatories – 　e.g. phenylbutazone ("Bute")　 The dosage and duration of the medication will depend on the severity and the response to treatment

•Acepromazine (Sedalin®) – helps correct the altered blood flow in the foot in the acute stages of the disease

•Dietary Restriction 　 　

◦Soak the hay (ideally for 2 hours) and rinse before feeding. This will decrease the water soluble carbohydrate (sugar) in the hay

•Limit concentrate feeding to all that is required to administer medication

•A feed balancer may be useful to ensure nutritional needs are met

•Assessment and Correction of the Mechanics of the Foot

•Frog supports

•Corrective farriery if hoof conformation is poor

•X-rays: - If there is any suspicion of pedal bone rotation, X-rays are required to assess the degree of movement. These will allow the farrier to dress the foot appropriately and help us give a realistic prognosis

•Hoof surgery, such as dorsal wall resection, may be needed in severe cases with pedal bone rotation

•Diagnosis and Treatment of Concurrent Systemic Disease

•Antibiotics (if concurrent infection)

•Anti-endotoxic treatment if required e.g. gut absorbents, flunixin

•Counter acidosis e.g. NaHCO3

•Fluids if systemically compromised

•Liquid paraffin if grain/lush pasture overload

•Investigation of Underlying Endocrine Diseases (Pituitary Pars Intermedia Dysfunction/Equine Cushing’s Disease and Equine Metabolic Syndrome) and treatment for these if present

PROGNOSIS

Always guarded for any animal. In general, ponies do far better than horses with similar changes. Many of the obese, unfit pony type laminitics will respond well to simple management changes.　Any animal that has had an episode of laminitis will always be at risk from further flare ups and owners should do all they can to prevent these.

•Avoid obesity/unfitness/stress

•Restrict access to lush pasture/excess concentrate and feed a sensible diet with regard to the needs of the individual e.g. twenty-year old pet pony compared to ten year old showjumper

•Regular foot trimming and shoeing with attention to good foot balance

•Improve horn quality

•Treat underlying endocrine diseases

•Attention to the post foaling mare especially in heavy horses

•Use frog supports prophylactically if at risk e.g. post-colic surgery.