We are growing closer to understanding laminitis in all its forms, reports Edd Knowles MRCVS of Bell Equine
The laminae bind the soft tissues and pedal bone within the hoof capsule to the hoof wall. Laminitis occurs when these delicate folds become inflamed, causing heat within the hoof and resulting pain.
We know that many different factors make laminitis more likely to occur, including breed, diet, exercise and other illnesses.
Yet we struggle to understand exactly what happens in the foot when laminitis develops, and why an individual suffers when similar horses kept in the same way don’t.
In the UK, laminitis has traditionally been blamed on management — especially excessive grazing on lush pasture. While this is certainly important in many cases, the complete picture is more complicated.
Some interesting findings have emerged lately. Signs of laminitis have been found in the fossils of horses’ ancestors, millions of years before they were domesticated, and in wild horses with little access to pasture.
Researchers have also identified that microscopic changes within the hoof are different depending on how the laminitis was caused.
Researchers previously looked for a single explanation to link the different causes and types of laminitis. The current thinking is that there are at least four types, which are not necessarily linked:
➤ Hormonal dysfunction: The major conditions linked to laminitis are equine metabolic syndrome and Cushing’s disease. These conditions probably affect how a horse’s hormones respond to his diet and account for most of the cases we see at pasture in the UK.
➤ Toxic shock: Laminitis can occur when a horse is severely ill with another condition — particularly one that affects the gut, such as diarrhoea.
➤ Opposite limb laminitis: If a horse has a severe lameness on one leg for a prolonged period, such as a fracture, he may develop laminitis in the opposite leg as it struggles to cope with the extra load.
➤ Repetitive strain: Signs of laminitis have been seen in wild horses roaming over large distances on hard terrain.
The past few years have seen advances in our understanding of each of these types of laminitis. Most importantly, we now recognise the vital differences between them.
There is no “silver bullet” treatment to cure all horses with laminitis, however, and the varied and complex nature of the condition means we are unlikely to find one.
Each case tends to be treated differently, using a combination of pain relief, either rest or limited exercise and farriery. Management of associated conditions, such as dietary changes in the case of equine metabolic syndrome, may also be necessary.
‘Remarkably little research’
Research has typically sought to understand the processes that cause laminitis at a microscopic level, so that new treatments can be designed.
Yet there has been remarkably little research into treatments already available — such as objective comparisons between different shoe types or studies to determine how long horses with laminitis should be rested.
Treatments have fallen in and out of favour over the years, with little understanding of which work best. This cycle will continue until we make better efforts to study the effects of laminitis treatments in the real world.
Recent work has explored interesting treatment alternatives. There has been an explosion of interest in treatment and management of the hormonal conditions associated with laminitis, and continuing research will undoubtedly result in further advances.
The muscle-relaxing substance Botox can reduce tension in the deep flexor tendon that contributes to rotation of the pedal bone within the hoof. Its use has been trialled in the US and the Netherlands, and on a few cases in the UK, with varied results.
Other findings include the discovery that applying ice to cool the feet of horses with diarrhoea may make them less likely to develop laminitis, plus the potential of human drugs paracetamol and pregabalin to relieve pain.
Another exciting possibility is the use of stem cells to improve healing of damaged laminae — a technique performed in the US with interesting results but still requiring further study.
How a wooden shoe can aid recovery from laminitis: US vet and farrier Dr Steve O’Grady DVM, MRCVS, from North Virginia Equine, explains.
In the acute stage of laminitis, therapy is medical and directed toward reducing inflammation. However, when there is displacement of the distal phalanx [pedal bone] within the hoof capsule, the condition becomes chronic and therapy is mechanical.
At this stage, farriery plays a major role in rehabilitation. Displacement of the distal phalanx within the hoof capsule can be in the form of rotation (at the toe or towards the side), distal displacement (sinking) or any combination.
Recently it has been recognised that it is a relatively common occurrence for horses to have unilateral displacement (rotation of the bone to one side) either alone or combined with rotation at the toe. It is therefore essential to take X-rays of both a lateral view and a view from the front to diagnose this form of displacement.
Each case of laminitis must be treated as an individual and not categorised as a group. Farriery for chronic laminitis generally remains based on the past experience of the attending vet/farrier or a favourite method, rather than on biomechanical principles.
The biomechanical principles are to redistribute weight-bearing away from the diseased laminae; to move the point of break-over to decrease the force in the toe when the horse moves; and to provide heel elevation (when necessary) to decrease forces exerted on the laminae by the deep digital flexor tendon.
The immediate objective of the hoof trim is to realign the ground surface of the hoof capsule with the solar surface of the distal phalanx.
To do this accurately and consistently requires radiographic guidance. The trim is then combined with some type of shoe that adheres to the biomechanical principles.
In my practice, the application of a wooden shoe has become very advantageous. Accompanied by the appropriate trim, it incorporates all the biomechanical principles and can be screwed on in a non-traumatic manner.
It offers an excellent transient device to bridge the gap from displacement of the bone within the hoof capsule back to the point where traditional remedial farriery can be used.
Who’s at risk? Dr Claire Wylie MRCVS of Rossdales Veterinary Surgeons discusses recent study results
Laminitis is particularly significant because it poses a threat to all adult horses and ponies, regardless of how well they are cared for.
Despite this, information on those most at risk has historically been limited.
UK researchers recently published the results of a nationwide study examining risk factors for veterinary-diagnosed laminitis. Over a two-year period, 30 vet practices submitted data on new cases of active laminitis.
Owners completed fact-finding questionnaires for 1,010 animals, comprising 191 laminitis cases plus 819 non-laminitic animals included as a comparison group.
The various factors associated with an increased risk of laminitis were weight gain in the previous three months; new access to grass in the previous four weeks; box rest in the previous week; owner-reported history of laminitis; lameness/foot-soreness after shoeing/trimming and increasing time since the last worming treatment.
Factors associated with a decreased risk of laminitis were taller animals, feeding of additional supplements in the previous week and transportation in the previous week.
Animals with pre-existing endocrinopathic disease (equine metabolic syndrome and Cushing’s disease) were also identified as being at an increased risk. This adds to the growing strength of evidence that these diseases may be responsible for the majority of laminitis cases we see.
Importantly, laminitis occurred throughout the year and should not be considered just a disease of springtime. In fact, laminitis may be even more likely to occur in other seasons, particularly if owners fail to implement appropriate preventive strategies at times they consider “safe”.
Some of these findings were novel and unexpected and require further investigation before any recommendations can be made.
➤ Owners can help by taking part in the ground-breaking CARE about laminitis study. Find out more at www.careaboutlaminitis.org.uk
Ref: Horse & Hound; 19 March 2015