Form VS use - Navicular and laminitis disease

Introduction

As we have been studying since the beginning of this class, human management of horses do not always fit the horse needs and is more designed to accommodate the human needs. Bad management and unsuitable use of the horse can create problems to the horse. Laminitis and navicular syndrome are two inflammatory disease that are handicapping health issues. They are serious illness that may end a horse athletic career or even be life threatening. Mechanism of those diseases, their link to human management and their prevention and curative techniques will be revised here.

1-      Navicular and laminitis, what is it? What are the causes, symptomes and treatments

Both diseases are affecting the feet, usually mainly the foreleg feet. Both can create a major limp, end the career of a horse or in extreme case his life. Laminitis affects the laminae and the distal phalanx (cf fig 1 ) and navicular affects the sesamoïde (navicular) bone, navicular bursa and deep digital flexor ligament (cf fig 1).

Fig. 1                                                                       

  

Figure 1 : Part of the hoof, with laminae structures
From: http://lakesidelivery.co.uk/laminitis/ (2014)

Laminitis
Laminitis is a disease affecting the laminae of the foot. Laminae is a dermis structure that provide an attachment between the inside of the foot and the hoof wall (Hood and al, 2013). In laminitis, this structure gets inflamed and causes great pain to the horse (McCurnin, 2010). When laminae get inflamed for too long, they can lead to a degenerative state where the dorsal laminar attachment detach from the insensitive laminae of the hoof wall. Distal phalanx (coffin bone) can then dethatch from the wall and rotate toward the solar surface, in severe cases it can rotate so much that it can perforate the sole. All this will altere the intern mechanic of the foot, which will result with a blood flow dysfunction within the foot. As consequences, it will cause problem with the wall cornification and growth (Hood and al. 2013). It can occur on the two front feet or all four feet, but sometimes, it can occur in one foot only, but this is more rare. This disease is more often seen in adult horses over one years old (McCurnin, 2010). Horse developing laminitis can have the following symptoms: hot hoof, reluctance or difficulty to move, increased digital pulse, they stand in a way that put weight on the hind limb (front limb are stretched in front of them and back end is more under them than usual), white line can begin to separate from the wall, founder ring can appear on the hoof wall and in severe case, the hoof can appear deformed (Hood and al. 2013, McCurnin, 2010, Loving, 2009).

Causes
The causes of laminitis are not 100% sure, there is a lot of good suspicions but not much proof. On the other hand, a lots of conditions can raise the chance to develop this problem. Those conditions do not mean that the horse will systematically develop laminitis, but it will increases the chances. When a horse has serious inflammatory problem or serious infection, it can result in an endotoxemia, which can increase the chances of developing the disease (McCurmin, 2010). This problem can also be caused by giving too much concentrates or sweet feeds, often offered to show horses to raise their energy intake. It can also be caused by an hormonal imbalance, like cushing disease or insulin resistance (McCurmin, 2010, Loving, 2009). A lot of other causes are suspected: dehydration, electrolytic imbalance, colic or mechanical problems like extreme bruises, overload of one foot or contusions on the foot (Loving, 2009).

Treatment
Treatments for all severity of laminitis will focus in reducing the inflammation (with medication or/and cold therapy) of the hoof and facilitate the digital blood flow (Loving, 2009). It will also focus on making the horse as comfortable as possible, by giving him analgesic medication for the pain and by using an external support for the distal phalanx (McCurmin, 2010, Loving, 2009).

Mechanical support for the distal phalanx can be provided by a lot of tools, like heart bar shoes, leather degree pad (often used with heart bar shoes), boots with gel pad, special boots that can be fixed to different degree pads. A more rudimentary but efficient tool is Styrofoam pad fixed with duck tape (Loving, 2009). Good trimming of the foot will be extremely important in the treatment part to make sure that pressure is well distributed and to reduce the deformation of the foot.

Oui c'est le même pieds, avant et après un parage

Concentrates and sweet feed need to be eliminated and a fat horse needs to lose weight to reduce pressure on the feet. Blood tests can be performed to look if the horse as any metabolic problems. If so, management of those problems will be necessary (Loving, 2009).

Comfort care are also important as the laminitic horse is in great pain and will spend more time lying down, so deep bedding is necessary.

Treatment for mild cases of laminitis will focus on rebalancing the hoof, rebalancing the diet, and manage pain and inflammation. For moderate cases orthopedic shoeing and reduction of intense activity can be added to the previous strategies and for more severe cases euthanasia can be the best option as horses will suffer too much.

Prognosis
It depends if there is a distal phalanx rotation, and if so, of the severity of this rotation (McCurnin, 2010). The more severe is the rotation, more dark is the prognostic. Horse can live well with a small rotation but can not often return to a full athletic career. More rarely, rotation can recover completely and the distal phalanx can return to zero degree of rotation. But owner still needs to keep an eye on his horse’s foot.

Navicular syndrome

Navicular syndrome is a wide term used to talk about the degenerative process of the navicular structure. Those structures are the sesamoïde bone (navicular bone), the navicular bursa, the deep digital flexor tendon, and the multiple ligaments that support the navicular bone (Loving, 2009). In most cases, navicular syndrome occur in the front feet and make the horse lame. This syndrome is degenerative and progress with time.  Horses between seven and fourteen years old are more at risk to develop this affection, but younger horses in intensive use can also develop it.
Symptom of this affection can be: short and stiff strides (Rose, 1995), foot tends to land toe first, horse will trip frequently, frequent bruises and abscesses, feet can appear smaller and contracted heels can develop (Loving, 2009).

Causes

Multiple factors can cause inflammation and lead to this degenerative problem. Bursitis or bone remodeling caused by repeated pressure between the flexors tendons and the sesamoïde bone or an increased load on the heels are some example of those factors (Loving, 2009). Recent study by Dr. Robert M. Bowker conclude that this problem is about all the feet, not only about the navicular structures (Loving, 2009). There are many structures in the foot and each one of them are related to each others. If one structure have a problem, it can cause a domino effect and affect the others.

Some characteristics can enhance the chances of a horse to develop navicular syndrome. Hereditary conformation problems like straight pastern or really small feet, comparatively to the body mass (Rose, 1995). Horses that are trained for disciplines where they are subject to repeated impact on the feet are also more at risk as it stresses the internal structures of the hoof (Rose, 1995). Some breeds tend to develop this syndrome more easily than other, Quarter Horse and Thoroughbred, for example, tend to be more at risk than Arabian (Loving, 2009, Rose, 1995). Bad hoof care and balance are also a factor, as they can put abnormal biomechanic stress on the navicular structures.

Treatment

The most important part of the treatment is to provide great foot care for the horse (Rose, 1995). Well balanced trim or shoeing is really an important step in the management process. It is important to provide good support at the back of the foot (Loving, 2009), this is why egg bar shoes are often used,

as they do not form a “U” shape like normal shoes but are in “O” shape, which provide the support needed to the heels. Some iron shoes coated with plastic can be used to help reducing the impact in the foot. More recently, synthetic flexible shoes appeared on the market, some of them are full shoes with frog support and have the advantage of being flexible and help to absorb choc (Loving, 2009).

In complement of a good hoof care, other strategies can be used to help managing this syndrome. Injectable drug like Polysulfated Glycosaminoglycan can delay the degeneration of the cartilage matrix. Intra-articular injections with corticosteroid can also provide pain relief to the horse. When none of the previous strategies can help pain management, palmar digital neurectomy can be performed (Loving, 2009). This procedure consist in removing the palmar digital nerves to remove the pain. This surgery can have many side effects, one of them is that horses will lose sensation in his foot, which can lead to concussion an bruising (Grant, 1997). This can also cause some horse to trip more often (Grant, 1997). owner should ask about them before taking any decision (Rose, 1995).  Navicular horses should be exercised and kept moving as this can help to keep a good blood supply and a good articular cartilage lubrication in the feet.

Prognosis

It depends of the severity of the damage of the navicular structures. The more severe are the damages, more dark is the prognostic. Some horses can have an athletic career, while some can’t. It really depends of the severity of each case and the ease to manage the pain.

2 - Human management, how is it responsible of these two diseases

 Human management methods are not always suitable to horses need, bad management and care can create handicapping problems for horses. It is important to know what can lead a horse to illness and try to avoid those practices.

Bad equine care and management can raise the chances of a horse to develop laminitis. Horses are often given too much concentrates and sweet feeds for their need. Hay and pasture are frequently too rich for the horses needs as well. This herbivorous animal is not conceived to ingest much of those simple sugar, he is designed to ingest cellulose, a complex sugar, which will slowly be degraded on the hind gut (Janis, 1976). Simple sugar like fructose and carbohydrate are absorbed too quickly by the small intestine, they are too easily available for the body and can cause inflammatory responses. As seen previously, constant inflammation can lead to laminitis. Feet care are not always at their best, sometimes it is because the feet are not well balanced (long toe, running heels) (Loving, 2012), they can be trimmed too short (which can lead to concussion laminitis) and sometimes hoof cares are not provided as often as it should (so feet are too long and deformed). There is also suspicion of dehydration and electrolytic imbalance in the possible cause for laminitis (McCurmin, 2010), horses need to have constant access to fresh water, which is not always the case. Horses that are showed can also be at risk of this, because stress and intense activity can lead to dehydration. Moreover, water in show can taste different than at home, which can prevent a horse to drink.

Bad management can also lead to navicular syndrome. Like in the laminitis causes, bad foot care is a major cause of the disease. Long toe, running heel type of foot can put more tension on the deep digital flexor tendon. In consequence, the tendon put more pressure on the sesamoïde bone and can lead to a premature use and to inflammation (Loving, 2012). Nutrition also plays a role in the management of navicular syndrome, as discussed above, too much weight on too small feet can enhance the chance of developping this problem. There is less bearing surface on the small hoof that can distribute the pressure, and there is more weight to carry, leading to more stress on the foot structures. Horses are also asked to perform in a lot of disciplines like reining, dressage, show jumping, eventing, barrel racing, etc. Those disciplines need fast speed, big jumps or both, this is putting more stress on the horse’s feet than if he was just walking around.

Good attention to management could help to reduce the horse’s risks of developping those diseases. Simple details can be looked at every day to try to have a more suitable horse management.

3-Prevention

 When we talk about preventive techniques, good practice can be to keep the hoof well balanced, to keep the horse fit and with a good weight (Loving, 2009). Horse should be kept moving, offering him frequent turnout will help to keep the foot structure strong and healthy. Too often, owner will keep their horse in a stalls to prevent them from injuries and not having to run after them in the field, but lack of movement can actually cause more bad than good and lead to more injuries (McGreevy, 2012). In the nutrition side, horses should always have access to fresh water, to avoid dehydration.  A good prevention to foot problems is also to be really careful not to give horses feed that is too rich for their needs, and if they need it, to fractionate the portion in multiple meals. Keeping horses in overweight is a bad idea, easy access to rich hay, concentrates and sweet feed have led many horses to obesity and andotoxemia, two major factor in the development of laminitis. Keeping an eye on the horses intake and needs is a good management strategy. In the contrary, horses that are put on a severe diet can develop other problems like gastric ulceration (McGreevy, 2012) or important muscular loss. Deprivation of enough hay or locomotion can lead equine to stereotypies and ulceres (McGreevy, 2012). Management should always take in consideration the behavioral need of the horse as well, because mental health is as important as physical health.

New fashion in the American horse industry is to have big muscled horses with small feet. There is less bearing surface on those small hooves to distribute the pressure, and more weight to carry as muscles are heavy. This put more pressure on the internal structures of the foot. These horses are then asked to perform at great speed, which will also increase the pressure on these tiny feet (Loving, 2012). All this can lead to navicular syndrome and this kind of breeding selection should be avoided in an attempt to produce healthy athletes. Owner must try to reduce chocs on the feet at the lowest possible level. Shoeing is often used to reduce the wear of the hoof, which work great for that purpose, but in the other hand, it reduces the expansion of the feet. This function is important in the choc absorption mechanism of the feet, and shoeing reduce that. So it’s a double-edged knife that should be taken into consideration before taking this decision.

Conclusion

Navicular syndrome and laminitis are two different diseases of the foot that can be related to  human use and management. Horses management is complex and requires knowledge from caretakers. It is important to find the right balance between the horses and the human needs in a way that enhance the welfare of the horse. Needs of the horse should always been taken in account before any decision making.

Bibliography

             Hood, David M. and Larson, Connie K. Building the equine hoof, by Zinpro performance minerals, 2013 zynpro corporation.

             McCurnin, Dennis M. and Bassert, Joanna M. Clinical textbook for veterinary technicians, P. 1068 - 1317, seventh edition, Saunders Elsevier, 2010

             S.Loving, Nancy, DVM, nouveau manuel vétérinaire pour propriétaire de chevaux, 2009, edition vigot, translated from English by Patrick Morin, DVM, originial version : All horse system go, 2006

             Rose, R.J, navicular disease in the horse, 1995, paper presented at the world equine veterinary association meeting held at Yokohama, Japan, published in the journal of equine veterinary science, volume 16, number 1, 1996

            Janis, C, The evolutionary strategy of the equidae and the origins of rumen and cecal digestion, museum of comparative zoology, Harvard university, Cambridge, Massachusetts, February 8, 1976

            McGreevy, P, Equine behavior a guide for veterinarians and equine scientists, second edition, saunders Elsevier, 2012

            Grant, Barrie, Neurectomy for navicular, Oct 1, 1997, http://www.thehorse.com/articles/10603/neurectomy-for-navicular