In the normal horse or pony the distal phalanx (coffin or pedal bone) is attached to the inside of the hoof by a tough, but flexible, suspensory apparatus. The surface of the inner hoof wall is folded into leaf-like lamellae (laminae) to increase the surface area of this suspensory apparatus.
A horse has laminitis when these lamellae suddenly fail. Without the distal phalanx properly attached to the inside of the hoof, the weight of the horse and the forces of locomotion drive the bone down into the hoof capsule. Important arteries and veins are sheared and crushed and the corium of the coronet and sole is damaged. There is unrelenting pain in the feet and a characteristic lameness (Figure 1.1)
Figure 1.1 The gait of a horse with severe laminitis. When a horse develops laminitis the front feet are usually the most severely affected. It is extremely painful for the horse to accept weight on the toes of the front feet, but if forced to walk (Obel grad 3 lameness), it will bring its hind legs well under and half near before stepping forward in front. The posterior of the foreleg stride is thus very much shortened. Large, heavy horses are often more severely affected by laminitis than small ponies.
The Problem of Laminitis
Laminitis is the most serious disease of the equine foot and causes pathological changes in anatomy that lead to long lasting, crippling changes in function (chronic laminitis or founder). It is the second biggest killer of horses after colic. In the USA National Animal Health Monitoring System (NAHMS) report of the year 2000, 13% of all horse establishments (excluding racetracks) had a horse with laminitis in the previous year and 4.7% of these died or were euthanased.
Laminitis has a developmental phase which lamellar separation is triggered.
This precedes the appearance of the foot pain of laminitis. The developmental period lasts 40-48 h in the case of laminitis caused by excessive ingestion of soluble, non-structural carbohydrates, such as starch or fructan. Sometimes no developmental phase can be recognised; the horse or pony is discovered in the acute phase of laminitis with no apparent ill health or inciting problem occurring beforehand. This appears to be the case with grass founder (laminitis resulting from the ingestion of lush pasture).
Many people own and care for horses all their lives and never encounter a horse with laminitis. However, when it does strike, laminitis can be heartbreaking. The pain and suffering are relentless and sometimes, euthanasia is the only responsible option for an owner, despite the stoic ability of many horses to live on as cripples. Formulating an effective management plan for a horse with laminitis is one of the most difficult tasks a horse owner can be confronted with. The owner, in consultation with a veterinary clinician and farrier, will have to decide if the investment of money, time and energy is worthwhile. After months of treatment and the expenditure of perhaps thousands of dollars, the horse in question may still be suffering severely.
The clinical signs, the extent and severity of lamellar pathology and the response to therapy vary unpredictably between individual horses and this makes a rational treatment strategy, with an accurate prognosis, difficult to formulate. Severe damage to the internal anatomy of the hoof can occur within the space of a few hours and the severity and extent of this initial damage is the single most important factor influencing the final outcome.
Scientific understanding of laminitis is incomplete and the horse owner often becomes committed to the symptomatic treatment of a chronic condition that inexorably deteriorates. This lack of understanding of the process involved is frustrating to the horse owner and veterinarian alike, and of little use to the horse. Over the last six years, the RIRDC horse programme has made understanding laminitis and seeking improved treatment strategies a priority. This report is the result of six years continuous RIRDC funding to the Australian Equine Laminitis Research Unit (AELRU) based in the School of Veterinary Science at The University of Queensland. It describes laminitis in the most up to date way possible, although there are still large gaps in our knowledge. To understand what goes wrong with an organ, it is essential to first learn about its normal structure and function. Thus, the first part of this publication details what is already known about lamellar anatomy and presents the results of research carried out at the AELRU on the structure and function of the normal horse's foot. This is followed by a description of the developmental mechanism of laminitis that has been elucidated from our findings. Finally, a review of first aid measures for the foundering horse is presented and ways and means of rehabilitation.
The hope is that a better understanding of laminitis will lead to a more unified approach and rational treatment, by owners, veterinarians and farriers alike.
Laminitis is caused by failure of the attachment of the distal phalanx to the lamellae on the inside of the hoof.
The disease causes pathological changes in hoof anatomy that cause crippling pain and a characteristic lameness
Specialist intervention is required in the treatment of laminitis, but the response to therapy can be unpredictable
Research that paves the way to a better understanding of laminitis may lead to more successful treatment of horses suffering from the disease