Navicular Disease.
By Professor J. Wortley Axe.
There is no disease which so seriously affects the feet of our horses as “navicular disease.” Its commencement is subtle and its progress so insidious that it is only when the malady has reached a dangerous condition that it becomes known to the ordinary horseman. At this stage veterinary aid is usually sought, with the result that the owner has to be told that nothing can be done in the way of cure and very little towards stemming its onward progress. Why, it may be asked, do we occupy the pages of this Magazine with a subject so absolutely devoid of matter to which attention can be profitably directed. Our reply is that if little can be done in these directions we are not without hope of ministering to its prevention, and for this we claim some justification for so far imposing on our readers.
Before the days of Moorcroft and Turner navicular disease, although much in existence, was not recognised by the profession, and the lameness arising out of it was referred to the shoulder, with no other reason, save that indications of disease were not detected or detectable in other parts of the limbs. Then, as now, the feet of horses were noticed to contract, and when this condition was found to exist the lameness was attributed to it, and it alone. No one seems to have thought to look for the cause of contraction, and thus to trace the fons et origo mali, but all remained satisfied that the lameness arose from the pinching of the sensitive structures of the foot by the contracting hoof.
No doubt in some measure this was true, for it is impossible to think of a normal state of the sensitive parts of a structure like the foot being enclosed within a small and contracted hoof. As a secondary cause, therefore, contraction would be sure to make itself felt sooner or later by diminishing the size of the foot and interfering with the play of the parts within.
The peculiar stilty action which this disease induces brought into use the term “chest founder.” This term was meant to convey the idea of pain in the muscles of the chest, where the disease giving rise to it was supposed to exist, and it was not until Moorcroft and Turner traced the disease to the navicular bone that these meaningless terms ceased of employment, and the much more rational one, “navicularthritis,” came to be used in their stead. Whether this term is an appropriate one or not may be open to question, but it locates the disease, and in this respect it is distinctly useful.
Causes.—We cannot speak of the cause of navicular disease without referring to the influence of heredity. There can be no doubt that the property of transferring to the offspring the weakness inherited by the parent is just as marked in this as in any other affection, and the writer, in a long experience, has seen numerous instances of the disease handed down from the latter to the former. It must be understood that the transmission of hereditary taint or predisposition is what is understood here by hereditary disease. It is not that the disease in an active state is born with the animal, but that the parts are in that condition in which the disease may be easily excited in them by causes which would not affect an animal who was not the subject of hereditary weakness. It must not however, be stated that because a horse inherits a predisposition to navicular or any other disease that he should necessarily contract it. A good deal will depend upon the degree of intensity of the inheritance on the one hand, and the severity of the cause which acts upon it on the other. If it exists in such form as to be easily excited into action, it is not unlikely to appear, but where the hereditary predisposition is only possessed in a mild measure the animal may not meet with a cause sufficiently severe by which the predisposition can be made to assume an active state.
Exciting Causes.—They are numerous and varied. Conformation, action, shoeing, weight of body and general management, all play their respective parts in causing the disease.
Side View of Healthy Foot.
Side View of Diseased Foot.
Back View of Healthy Foot.
Back View of Diseased Foot.
As to conformation, it would seem that the more upright the parts below the fetlock joint, the less elasticity they present, and the more do they assume a mere column of support. In this case the weight of the body falls more directly upon the navicular bone, and the absence of that elastic recoil afforded by the oblique pastern tends to excite disease in it.
Action.—This will commend itself as an exciting cause to anyone who will watch the movement of different horses. The animal who lifts his limbs high in the air and brings them down again almost in the place from which he took them is much more likely to contract the disease than the horse whose movements are less exalted and more progressive. Especially is this the case if the body is loaded with flesh and the horse is in soft condition.
Shoeing.—Notwithstanding the very great benefits which have resulted to shoeing smiths from recent efforts in their behalf by Agricultural Societies and County Councils, there still remains much to be done ere we can claim to have placed the shoeing of horses outside the causes of navicular disease.
It is perfectly true that the impression left on the mind of a visitor to agricultural shows where shoeing competitions are in evidence is usually assuring, but it gives no idea of the general unfitness of the great bulk of the craft to follow the chosen calling of their lives. This is said in no want of respect for the shoeing smith, but rather with the object of drawing attention to him as a much-neglected individual, and one who is always thankful for anything that may be done for him in the way of education.
Paring the sole, the frog and the bars are all still in evidence both in town and country, but it is not always the wish of the shoeing smith that it should be so; too often it is the wish—nay, the will—of the owner or the coachman that the feet shall look smart, and in order to do this the smith abandons his better knowledge to “oblige.”
Nothing tends so much to lay the foundation for navicular disease as the repeated mutilation of these parts in shoeing. The sole, the frog and the bars are together designed among other things to keep the heels apart and protect the sensitive structures within, and notwithstanding this there are still those who for reasons of their own continue to disregard this very obvious truth and to insist on their horses’ feet being cut out of shape and weakened to the last degree. It is never given a thought that thickness of sole and frog is a defensive quality, and to cut them is to weaken them and to expose the parts within to pressure from without. Apart from bearing their share of the weight of the body, the bars are specially intended to keep the heels open and to maintain a healthy state of the foot, which cannot possibly exist where they are repeatedly cut away in the act of shoeing.
Navicular Bone.| Showing Small Ulcers invading its Structures.
Calks, and such means as are adopted to remove the frog from the ground, operate unfavourably on the feet, and especially where mutilation is part of the operation of shoeing.
Contraction of the foot not infrequently results where the hoof is allowed to grow unduly long and the frog is removed from the ground, or where, as the result of injury to some part of the limb, the foot is rested for a long period. Whether the result of the one cause or the other, it is a condition which, if not carefully rectified by shoeing, may excite navicular disease.
It is comparatively seldom that navicular disease is found to exist in the hind feet, and the preference which it shows for the fore ones may possibly be found in the difference which exists in the conformation of the limbs. The straight fore-leg allows the weight to fall directly on to the feet, while in the hind one it is first broken and diffused in passing through the angle forming the hock, so that by the time it reaches the foot the sharp edge of concussion is removed and the foot escapes the injury which is inflicted through the straighter column in front.
Prevalence of the Disease.—As to the horses which suffer from this affection, it may be somewhat difficult to say in which particular variety it is most prevalent. Between the light and heavy horses there is a great difference in favour of the latter, although since they have been called upon to do so much trotting work the malady has increased in the same proportion. There is a much greater number of cases among harness horses than any other description, but it must not be forgotten that they are the more numerous. And on this account we should look for more cases than are to be found in the other varieties.
Hunters are frequently found to be affected by navicular disease, although their work is for the most part over soft, yielding ground. These animals suffer most when made to jump from high banks into roads, especially when the muscles are tired and have lost much of their power. In these circumstances the full weight of the body falls upon the feet, with the result that the navicular bone may suffer by impact with the ground and become the seat of disease. But apart from these special accidents, hunters become subjects of the malady as the result of constant wear.
The racehorse, as such, is comparatively seldom the victim of this affection. So long as he is in training he is constantly on the turf, and at an early period is relegated to the stud, and ceases to be exposed to the causes by which the disease is excited. If, however, he does not himself contract the malady, his peculiar habits of life have a tendency to weaken the feet and to predispose his stock to contract the disease. In this way he becomes a factor in its propagation. His constant absence from the hard road does little to encourage the secretion of a thick, strong horn, and to impart to the feet that flinty hardness so much to be admired in a sire. “No foot, no horse,” is an axiom as true to-day as it was when first formulated by Lafosse. This is not said to prejudice the thoroughbred, for which the writer has a very high regard as a sire both of hunters and harness horses, but rather to hold out the caution to those who use him.
Symptoms.—There are few diseases in which the symptoms are so obscure and ill-defined in the earlier stages as they are in navicular disease.
The situation of the injured part forbids that inspection and manipulation which we may readily apply to other diseases, and there is too frequently no visible effects of the injury to guide the expert, but only an insidious and slowly progressive lameness.
It is more than probable that for some time the owner will be in doubt as to whether there is any defect at all. The only change observable to him is an uneasy sensation experienced when the horse is ridden in his fast paces. Soon, however, the defect becomes obvious in one leg or the other, and later in both.
At this time careful search may or may not discover visible contraction of the diseased foot. This condition, however, soon follows on by resting the foot in the stable or relieving it when at work. In the former case it is partially flexed and advanced more or less so as to take it away from the bearing, and in the latter the heel is kept as far as possible from the ground, and the weight is thrown on to the front part of the foot. All the changes which follow upon this are in the direction of contraction of the heels, and as this takes place the foot narrows behind. With the progress of the disease and the constant use of the sound foot it also begins to show signs of trouble, and the lameness which had hitherto been confined to the one now appears in the other. Knee action becomes defective, the step is short and “proppy,” or, as it is commonly expressed, “groggy.” On leaving the stable the horse is very lame, but as he continues to move the lameness in great measure passes away. The fore limbs are now upright, or he stands over at the knees, a fulness appears in the hollow of the heel, the foot becomes blocky, and the crust thick and dense, the sole is unusually concave, the frog wasted, and may be affected with thrush.
Treatment.—It may be accepted as true that once the disease is started its progress continues, and sooner or later brings its victim to the knacker’s.
In some horses the malady makes slow progress, but in others it is rapid and destructive. If the disease cannot be cured by the adoption of palliative treatment, much useful work may be obtained from an animal affected by it. When navicular disease is known to exist, special attention will, of course, be given to the shoeing. Here much may be done to keep the disease in check.
We see by the concavity of the sole and the contraction of the heels that the latter have not been allowed to come to the ground in the ordinary way. This is the keynote to which attention must be directed in regard to treatment. The heels must be defended by slightly thickening the shoe at this point, and the introduction of a leather or india-rubber band to break the jar on concussion.
The crust must not be allowed to grow unduly, but must be kept down by occasional rasping. By doing this, contraction of the foot is to some extent prevented, and the conditions of its elasticity preserved.
When in the stable a cold wet swab should be worn; it softens the hoof, prevents contraction, and enables the animal to work with comparative ease. Horses with navicular disease, especially those advanced in years, should be kept at work. Of all occupations none suit these animals like working on the land, where the feet meet with the least resistance. Mild counter-irritants to the coronets while still working may be applied, but on no account should the animal be allowed a “long rest,” during which he loses condition, and with it all the courage by which he has been enabled to “suffer and to work.”
The last and final act in the treatment of navicular disease is division of the plantar nerves.
THE BEECH.
The effect of this operation is not to cure the disease, but by severing all connection with the brain, to prolong his working powers. This done, the animal ceases to feel the pain which troubled him before, and commences to use the diseased foot without giving it the slightest protection. The lameness, which was evidence of the care he bestowed upon it, passes away, and the foot, weakened by disease, resumes the work it did when in a sound condition. This tends to aggravate the mischief, and sooner or later to bring him to the hands of the knacker.