By: Dr. Andrew Van Eps
One of the evolutionary adaptations that has defined the horse and other Equus species as amazing athletes is their feet. Horses have a single hoof that encases and supports the column of bones in each limb enabling them to run fast on all kinds of terrain. The hard, horny hoof is attached to the underlying pedal bone (‘coffin bone’/ third phalanx / P3) by intricate soft tissue attachments called lamellae (previously termed laminae). These lamellae suspend the horses’ weight within the four hoof capsules, but at the same time, amazingly, they allow the hoof horn to grow down to replenish itself when worn, while also retaining the strong bond between the hoof and pedal bone. When the lamellae suffer disease and become inflamed the term ‘laminitis’ is used.
Laminitis results in the structural integrity of the laminae being compromised, and the weight of the horse can then cause the pedal bone to pull away from its hoof capsule attachments. This can be just over the toe area, in which case the pedal bone may rotate away from the hoof wall, or it may be circumferential, in which case the pedal bone sinks in the hoof capsule and can even penetrate the sole of the foot. Rotation of the pedal bone tends not to be as serious as ‘sinking’, which is typically a situation that calls for humane destruction.
Laminitis, also known as founder, can be a very painful condition in both acute and chronic forms and represents a major welfare issue for horses. Sadly, laminitis can lead to a horse being euthanized on humane grounds to prevent long term suffering. Horses, being animals of the Plains, do not like to spend much time lying down and, more importantly, suffer from other problems like colic, muscle problems, and bedsores, if they do stay recumbent for any substantial length of time. These significant constraints confound our ability to help horses with severe laminitis as we cannot simply prescribe ‘bedrest’ as we might for a human.
The causes of laminitis are broadly divided into three main categories with the end result being weakening of the bond between hoof capsule and pedal bone via damage to and dysfunction of the laminae. The three broad issues that can lead to laminitis are (1) Sepsis or endotoxemia. For example, as might occur with a severe gastrointestinal disease such as colitis. (2) Endocrine Disease. In horses with endocrine disease such as Equine Metabolic Syndrome, deranged hormone levels and insulin dysregulation make them prone to laminitis. (3) Trauma such as excessive weight bearing.
In active racehorses, endocrine disease is extremely rare. If laminitis is diagnosed in a racehorse, it is more likely to be related to sepsis from other disease, such as colitis, or from excessive weight bearing as can occur when they have a painful condition such as a bone fracture. As discussed in other LUR website articles, the importance of making sure horses are comfortable when they have a serious injury, like a surgically repaired bone fracture, is absolutely critical to their survival. If the repaired limb is not strong enough or comfortable enough to share weightbearing then the contralateral limb is excessively loaded and can develop weightbearing laminitis.
Laminitis research, as well as ongoing research into related areas such as improved disease prevention and treatment, injury prevention, and advances in fracture repair, pain management and rehabilitation strategies is key to our ability to prevent laminitis and reduce its impact as a life-threatening welfare issue for horses.
