Diseases of the Horse's Foot Part 12

The long-continued inflammation, although only of a low type, renders the horn of the hoof hard and dry, and only with difficulty will the ordinary foot instruments cut it. This in its turn leads to cracks and fissures in various places, but more especially in the bars and what is left of the frog. Often, too, cracks will appear in the horn of the quarters, and a troublesome and incurable form of sand-crack results.

An animal with contraction advanced as far as this, especially if confined to one foot, goes unmistakably lame. With both feet affected, he ordinarily starts out from the stable in a manner that is commonly called 'groggy.' In other words, the gait is uncertain, and feeling; and stumbling is frequent.

Anyone who has had the misfortune to drive an animal with feet in this condition knows full well that every little irregularity in the road at once makes itself felt to the feet, and that the animal, as time goes on, learns to carefully avoid any suspicious-looking group of stones he may see. To drive an animal like this is to keep one's self continually on tenter-hooks, for, sooner or later, the inevitable happens, and the animal comes down.

Up to now we have described the changes of form in the hoof as seen when the contracted foot is viewed from the solar surface. With those changes as evident as we have depicted them, there will be no difficulty in detecting the alterations in the form of the wall.

In addition to a narrowing from side to side there will be noticed an abnormal straightness of the quarters, with a turning in, more or less sudden, of the heels. This effect is given in these cases by the smith maintaining the shoe of a length and width that should normally fit a foot of that particular animal's size and substance. This is probably done with the idea of deceiving anyone examining the solar surface. Viewed from this position, the width of the shoe at the heels gives the impression that it is attached to a foot of normal breadth. This deception is heightened if at the same time has been practised the process of 'opening up the heels.'

That expression indicates that the bars have been removed, and the lateral lacunae of the frog made to continue the concavity of the sole. The arch of the latter is thus made to appear of much greater extent than it really is, and the heels, by reason of their being abruptly cut off when removing the bars, also convey the false impression of being wide apart.

The pract.i.tioner unversed in the tricks of the forge will best guard against this by viewing the foot, while on the ground, from behind. From that position he will be able to detect the lowness of the quarters, and the projecting portion of the shoe, that the hoof, by reason of its sudden bending inwards, does not touch.

The 'feeling' manner of the gait before alluded to, together with the disinclination to put the foot firmly and squarely forward, will sometimes lead the examiner to over-look the contraction, and diagnose his case as one of shoulder lameness. In many cases, too, such consequent conditions as 'thrushy frogs' and 'suppurating corns' are often treated with utter disregard of the contraction that has really brought them about. But above all, the disease most likely to be confounded with simple contraction is navicular disease. More than probable it is that many cases of so-called 'navicular' have in reality been nothing more than contraction brought about by one or other of the causes we shall afterwards enumerate--cases where a due attention to the prime cause of the mischief would, in all likelihood, have remedied the lameness.

_Changes in the Internal Structures_.--It follows as a matter of course that the changes we have described in the form of the hoof itself carry with them alterations in the bones and sensitive structures beneath it. The tissues, as a whole, become atrophied. The os pedis becomes deformed, loses its circular shape, and gradually becomes more or less oval in contour.

At the same time, its structure becomes more compact, the cribriform appearance of its anterior and lateral faces more or less destroyed, and the few remaining openings apparently increased in size. This atrophy of the os pedis is best noted at the wings.

In the plantar cushion the effects of the atrophy are noted in the smallness of the organ, in its becoming whiter in colour than normal, and more resistant to pressure.

The coronary cushion is also affected in the same way, where the changes are noted most in its posterior portions.

A further effect of the narrowing of the heels, and their consequent tendency to drop downwards, is the exertion of a continual pressure on the sensitive sole. In course of time, and especially in flat feet, this leads to the appearance of corns.

The navicular bone and bursa and the tendon of the perforans also suffer from the effects of compression. The movement of the tendon is restricted, and arterial supply to the adjacent structures rendered deficient. The tissues of the bone and bursa are insufficiently nourished, and the secretion of synovia lessened. In this way it is conceivable that navicular disease may follow the condition of simple contracted heels.

In common with the other structures, the lateral cartilages also suffer from the continual pressure. Their blood-supply is lessened, their functions interfered with, and side-bones result.

_Causes_.--Upon the causation of contraction a very great deal has been written, both by early veterinarians and by those of the present day. Many and widely differing opinions have been advanced, but a careful resume of only a few will lead one to certain fixed conclusions.

We may consider the causes of contraction under two headings--predisposing and exciting.

_Predisposing Causes of Contraction_.--Among these we will first mention heredity, although it is possible it should not be deemed of so great account as it is by some. That the shape of certain feet, especially those with low heels and abnormally sloping walls, predisposes to contraction no one will deny. So long, however, as the animal goes unshod, so long does the foot maintain a normal condition of the heels. In other words, it is not until the tendency to contraction already there is aggravated by careless shoeing and the effects of work that it operates to any noticeable extent.

The degree of contraction will also be very largely governed by the amount of the development of the frog. With a frog of good size, low down, and taking part in the pressure of the foot on the ground, contraction will be prevented. On the other hand, an ill-developed frog, one wasted by long-continued and spreading thrush, or one robbed of its normal function by excessive paring in the forge, is a common starting-point of the condition we are considering. We have already referred to this in Chapter III., when considering the experiments of Lungwitz in this connection. What we have to bear in mind in these experiments is that the application of a pad to the frog, in such a manner that effective ground-pressure is obtained, results always in a marked expansion of the heels, and that, with counter-pressure with the ground absent, expansion occurs to little or no extent. This is proof positive of the enormous part the frog plays in maintaining an open and elastic condition of the heels--a fact so insisted on by Coleman.

It is worthy of mention, however, that loss of the frog's function does not operate to nearly so serious an extent in horses with high, upright heels as in those with the heels low and excessively sloping.

In ill.u.s.trating this, Mr. Dollar, in his work on shoeing, mentions the case of a pair of trotting horses of similar age, size, and weight, each having weak fore-heels. In one case the hoofs were flat, in the other upright. The horse with the flat hoofs suffered from contraction, while the other did not.

The reason appears to be that in the animal with upright hoofs the proportion of body-weight borne by the heels is considerably less than in those with the hoofs flat and sloping.

Certain conditions of the horn-producing membranes also predispose to contraction. For example, in horses reared on marshy soils, and afterwards transferred to standing in town stables, we find that a dry and brittle condition of the horn supervenes. This we may regard as a low form of laminitis, brought about by the heat of the material upon which the animal is standing, and the congestion of the feet engendered by his enforced standing for long periods in one position, as opposed to the more or less continuous exercise when at pasture. With the hoof in this condition it loses by evaporation the moisture that normally it should contain, and, as we might expect, a certain degree of contraction of its structure is the inevitable result.

We thus see that contraction brought about in this way is not so much caused by the heat of the stable, as it is by the decreased ability of the horn to retain its own moisture.

On the other hand, it cannot be denied that excessive warmth and dryness combined tend also to an undue abstraction of moisture, even from the horn of the healthy foot; and this explains in great measure how it is that lameness, as a rule, and especially that proceeding from contracted heels, is far more frequent and of greater intensity in the hot, dry months of summer, than in the cooler and more humid atmosphere of winter. It is interesting to note, too, that an alternation of humidity and dryness is far more liable to injure the quality of the horn and tend to its contraction than the long-continued effects of dryness alone. A common ill.u.s.tration of this is to be found in the effects of the ordinary poultice. Everyone knows that when, after a few days' application, they are discontinued, we get as a result an abnormally dry and brittle state of the horn. This is doubtless due to the poultice removing the thin, varnish-like, and protective pellicle known as the periople, and thereby allowing the process of evaporation to act on the water normally contained in the hoof.

_Exciting Causes of Contraction_.--Among these, first place must undoubtedly be given to shoeing. This does not necessarily imply shoeing more than ordinarily faulty, nor a faulty preparation of the foot, but shoeing as it is generally practised. No ordinary shoe, except a few devised for the purpose, such as the Charlier or the tip, allows the frog to come in contact with the ground. This we take to be the main factor in the causation of contracted heels, especially with a predisposition already present in the foot itself. In the words of Lungwitz: 'Regarded from this point of view, there is no greater evil than shoeing. It abolishes the necessary counter-pressure, and thus interferes with expansion. Bars, sole, and frog cannot perform the functions that naturally belong to them as they would do without the shoe.'

In addition to the evil of the shoe itself, errors of practice in the forge contribute to the causation of contraction. Taking first the preparation of the foot, we find that often the heels are lowered far too much, and the toe allowed to remain too long. This can have but one effect--that of throwing a greater proportion of the animal's weight upon the heels than properly they should bear, with, what we now know to be the consequence of that, a corresponding pushing inwards and downwards of the horn; in other words, contraction.

Excessive paring of the bars, to which we have already partly alluded, is also an active agent in bringing about an inward growth of the horn of the heels and quarters. The bar, or inflexion of the wall at the heel, by means of its close contact with the frog, communicates the outward movements of that organ to the wall of the hoof. With the bar removed, the outward movements of the frog under pressure are naturally rendered of no account, and a proper and intermittent expansion of the wall denied it. The same evil follows, though to a less extent, excessive paring of the sole.

The shape of the bearing surface of the shoe is often to be blamed. Where this is concave--'seated'--and the 'seating' is carried back to the heels, it is easy to see that, when weight is on the foot, there is an ever-present tendency for the bearing edge of the wall to slide down towards the inner edge of the shoe. This tendency, operating on both the inner and outer wall simultaneously, must strongly favour contraction.

A further wrong practice is that of continuing the nailing too far towards the heels. In our opinion this is not now often met with. When it occurs its effect is, of course, to prevent those movements of expansion of the wall which we now know to be normal and most marked at the heels.

It may be remarked of the build of the shoe, or of errors in the preparation of the foot, that neither are of much moment. Neither are they. But when one stays to consider that errors of this description are practised not only once, but each time the horse goes to the forge, and that with some of them--those relating to the build of the shoe--the injury thereby brought about is inflicted not only once, but every day that particular shoe is worn, then it is not to be wondered at that, sooner or later, ill consequences more or less grave result.

_Prognosis_.--This will depend to a very large extent upon the conformation of the limb, and upon the previous duration of the contraction. Contraction of long standing, where atrophy of the sub-lying, soft structures and the pedal bone may be expected, will prove obstinate to treatment. Especially will this be so if the lateral cartilages have become ossified. Neither may we look for much benefit from treatment if the contraction has occurred in animals with an oblique foot axis and flat hoofs.

On the other hand, if the case is comparatively recent, if the limb is straight and the form of the hoof is upright, and if matters are uncomplicated by side-bones, or other serious alteration in the internal structures, then treatment may be rewarded with some measure of success.

[Ill.u.s.tration: FIG. 63.--TIP SHOE. The dotted portions represent the length of the branches removed.]

_Treatment_.--The greater part of the treatment of contracted foot will almost suggest itself as a corollary of the causes we have enumerated. The normal width of the heels may be renewed, and development of the wasted frog brought about by one of three methods:

1. By restoring the pressure from below to the frog.

2. By the use of an expansion shoe.

3. By operative measures upon the horn of the wall.

1. _By Restoring the Pressure from Below to the Frog_.

This may be accomplished as follows:

_(a) By Shoeing with Tips_.--This method is advocated by Percival, by A.A.

Holcombe, D.V.S., Inspector. Bureau of Animal Industry, U.S.A., by Dollar in his work on horseshoeing, and by many others.

Though requiring more care than in fitting the ordinary shoe, the application of a tip is simple. In reality, the tip is just an ordinary shoe shortened by truncating the heels.

Before applying the tip, the horn of the wall at the toe should be shortened sufficiently to prevent any undue obliquity of the hoof, and the foot should be so prepared as to allow the heels of the tip to sink flush with the bearing edge of the wall behind it.

When the foot does not allow of the removal of much horn at the toe, what is termed a 'thinned' tip is to be preferred. Its shape is sufficiently shown by the accompanying figure (Fig. 65).

With the tip the posterior half of the foot is allowed to come into contact with the ground, and the object we are striving for--namely, frog pressure, and greater facilities for alternate expansion and contraction of the heels--is thus brought about.

[Ill.u.s.tration: FIG. 64.--THE TIP SHOE 'LET IN THE FOOT.]

[Ill.u.s.tration: FIG. 65.--THE THINNED TIP.]

_(b) By Shoeing with the Charlier_.--The results brought about by the use of a tip may be arrived at by the application of a Charlier or preplantar shoe, or by a modified Charlier or Charlier tip.

Briefly described, a Charlier is a shoe that allows the sole and the frog to come to the ground exactly as in the unshod foot. This is accomplished by running a groove round the inferior edge of the hoof by removing a portion of the bearing edge of the wall with a specially devised drawing-knife. Into this groove is fitted a narrow and somewhat deep shoe, made, preferably, of a mixture of iron and steel, and forged in such a manner that its front or outer surface follows the outer slope of the wall.

The Charlier should have the inner edge of its upper surface very slightly bevelled, in order to prevent any pressure on the sensitive sole, and should be provided with from four to six nail-holes. These latter should be small in size and conical in shape. The nails themselves should be small, and have a conical head and neck, to fit into the nail-hole of the shoe.

[Ill.u.s.tration: FIG. 66.--THE SPECIAL DRAWING-KNIFE (FLEMING'S) FOR PREPARING THE FOOT FOR THE CHARLIER SHOE.]