The crust or wall of the hoof is composed of two layers: an outer one made up of closely-packed horn fibres, and an inner one composed of horny laminae. In a normal condition these parts blend with each other in close union, forming one solid, continuous whole.
In the condition known as seedy toe, the horn uniting them undergoes decay and breaks up into a blackish-gray granular-looking debris, which, when removed, leaves behind a space or gap between them.
Although termed seedy toe, the disease is not confined to the part indicated, but is frequently found to exist in the quarters, and sometimes to extend round the hoof from one part to the other.
In its more limited form it presents a superficial hollow in the toe, but it may extend upward to any height towards the coronet. It is not confined to any particular description of hoof. Horses with strong feet as well as others whose feet are weak are alike affected by it. An attack of laminitis imparts a special predisposition to it.
Lameness may not exist until the disease has made considerable advance, and it is in consequence frequently found when not suspected.
Fig. 391. - Seedy Toe. Vertical and transverse sections of foot, showing the horn fibres (o) separated from the horn laminae (b).
Save in exceptional cases, it is amenable to treatment, although frequently demanding a long period of rest.
Various causes have been assigned for this morbid condition of the hoof horn. By some it has been referred to injury done by the clip of the shoe. By others to "long-continued strain on the feet which was not sufficient to produce actual laminitis", and to the "weight-bearing surface of the foot being limited to the wall by bad shoeing"; while others again regard it as the result of the repeated application of excessive heat in the fitting of the shoe. Injury inflicted upon the horn-secreting structures of the crust by blows applied to the coronet has also been thought by some to be a sufficient cause. This, however, has been objected to on account of the disintegrated horn never being found at the coronet, or in any part of the crust, excepting when associated with a hole in the toe, from which it has been concluded that the disease commences below and extends upwards. It appears to us that no explanation of the origin of seedy toe will suffice which does not embrace and answer this objection.
In this connection we are of opinion that the foundation of seedy toe is sometimes, if not always, laid by an injury to the coronet, provoking the secretion of a loose and defective horn, and that the seedy or disintegrated condition in which it is found does not follow until this part of the crust has grown down to the ground and the degraded horn has become exposed to dirt and moisture. Under the influence of the latter it breaks up into the small seed-like particles from which its name has been derived.
In 1884 Professor Axe called attention to a nematode worm which he had discovered while microscopically examining the horny debris from a diseased hoof. In reporting the case in the Veterinarian he speaks of finding "thousands of minute, elongated parasites, with their ova, larvae, and structural remains". The late Professor Cobbold recognized the possible importance of the find, and from his knowledge of the structure and the habits of kindred parasites he had no hesitation in assuring Professor Axe "of their capability to permeate and break down the structure of the hoof in the manner observed in seedy toe". How they are enabled to accomplish this feat of destruction he explained by referring to "a formidable boring-tooth or spike with which they are armed at their oral extremity".
Professor Axe points out that these parasites are not always to be detected in seedy feet; but it seems quite clear, from the numbers in which they existed in the specimen referred to, that they had found an "agreeable nidus for their growth, development, and propagation", and by their presence and peculiar armature must contribute in no small measure to the extension of the disease whenever they gain an entrance to the hoof, which Professor Axe points out they may do in an ordinary way through cracks and old nail holes.
Dr. Cobbold provisionally named the parasite Pelodera Axei and described it as follows: -
"Mouth with broad vestibule and horny style; oesophagus long, with a large round bulb below, armed with dental plates; tail in both sexes long, subulate, very finely pointed; male with two short, nearly equal spicules, no bursa; female viviparous."
"Habitat. - Hoof of the horse (Equus eaballus)."
"Measurements. - Males 1/30 of an inch long, females 1/25 inch; breadth of the male 1/650 inch, and of the female 1/400 inch; length of longer spicule 1/650 inch, of the boring tooth 1/1000 inch; 5 length of the larvae from 1/200 to 1/50 inch; ovum, with coiled embryo, 1/500 inch by 1/850 inch; reproductive and anal outlet in the male placed 1/150 of an inch above the point of the tail."
Professor Angelo Baldoni of Bologna says the cause of seedy toe is a mould which he terms Achorion Kerathophagus, whose peculiar culture ground is horny tissue.
As in these cases a hole exists in the crust, and there is no possibility of bringing about a reunion of the two layers, the most radical and successful method of procedure is to remove all the outer fibrous layer from the toe upwards to a point where separation ceases. By this means the cavity is done away with, and the accumulation of dirt and moisture, which acts prejudicially upon the horn, is prevented.
It now remains to await the reproduction of the parts removed and the downward growth of a sound hoof.
As a means of expediting this, a little weak ointment of can-tharides or the biniodide of mercury may be applied round the coronet, and repeated at intervals of seven to ten days during a run at grass. A light bar shoe, thin at the heels, should be applied to the foot, so that the weight of the body is made to fall backwards and relieve the weak crust in front. Where a pasture is not available, the horse should be made to stand on peatmoss, tan, or saw-dust, and have a wet swab constantly applied to the crust.
Where little or no lameness exists, it is sometimes found desirable to continue the horse in work until a more convenient time arrives for subjecting him to the operation. When this is decided upon, the "seedy" matter should be removed from the crack, and the cavity, after being washed out with a solution of carbolic acid, well packed with tow and a composition of tar and grease.
Fig. 392. - Pelodera Axei.
1. Male. 2. Female. 3. Portion of female containing young. 4. Young female.