As emphasizing the importance of such external irritants and infections, it should be noted that the disease bears an appreciable relation to the filth and wet of the stable and farm yard, and to the absence of cleanliness in dealing with the feet, and that the extension of good pavement and protection from road mud have invariably lessened its prevalence. The irritant action of the urine renders mares more susceptible in the hind limbs than horses.
Symptoms. The disease may appear as a swelling, heat and tenderness of the hollow back of the pastern, involving the fetlock and lower part of the metatarsus or metacarpus, and this may last for one or two weeks, the engorgement lessening or disappearing during exercise and reappearing when at rest in the stall. The local tenderness is great as manifested by the prompt and excessive lifting of the leg when the heel is touched, as well as by the lameness when first moved, which subsides with further exercise. Itching may be shown by kicking the floor, or by a disposition to rub the pastern. The hairs of the affected part are rigidly erect, and a slightly moist, soapy sensation is felt on the skin. Close examination may detect the presence of small vesicles with as yet limpid contents, but the greater part of the liquid product is traceable to the openings of the hairs and gland ducts. This is followed by small excoriations taking the place of the ruptured vesicles, and the discharge becomes more profuse, opaque, white or grayish white, sticky, and fœtid. It covers the entire affected surface, mats together the hair in tufts and forms a thicker grayish border. The hairs are loosened in their follicles and easily pulled out. The erosions become complicated by chaps, and the swelling increases around the pastern and above the fetlock. When at rest in the stall the foot may be rested on the toe only, or held suspended and occasionally kicked backward as if to dislodge the cause of irritation, yet if moved the patient may gradually get over the greater part of the lameness, and the swelling partially subside.
In severe, protracted cases the discharge becomes essentially purulent, but often with a darker, greenish, reddish or blackish tinge, and portions of the skin may slough, leaving deep intractable sores. Still more commonly the raw surfaces become the seat of hypertrophied granulations, which grow out to form raw, red fungous like, pediculated neoplasms familiarly known as grapes. Between these the spaces are filled with tufts of hairs and the condensed discharges, in process of active septic change, and giving off a most repulsive odor. Like the preceding eruption these grapes may extend around the front and sides of the pastern, and upward beyond the fetlock, but especially behind.
This advanced condition shows no tendency to spontaneous recovery and the connective tissue and lymphatic plexus becoming involved, the leg often swells to enormous dimensions, from six to twelve inches in diameter at the fetlock. It may last indefinitely until the patient is worn out, or it may extend to other organs by contiguity or embolism. Canker of the frog and sole, fistula (quittor), sand crack and seedy toe may be named as complications, also septicæmia or pyæmia with abscesses in the lungs, liver, brain or bowels.
Lesions. In the first stage there is mainly the congestion of the skin extending into the large and numerous hair follicles of the pastern. If pressed, a transparent serum bedews the surface, and if sectioned the follicles around the hair bulb are seen to be distended by a similar product. The hairs are easily pulled out. The subcutaneous connective tissue is filled with a yellowish serosity and at intervals may be seen a red point of vascular stagnation or blocking. Later these products are more abundant and those on the now swollen and excoriated surface are distinctly fœtid. The infiltrated lymph plexuses in the connective tissue are more distended, their walls thickened and consolidated, and the rigid skin is thus firmly bound to the structures beneath. A careful examination shows the presence of subepidermic vesicles of various sizes. The congestion may extend deep enough to involve the periosteum of the digital bones and the ligaments of the joints. The grapes are each attached by a pedicle from which branch out cauliflower-like, fine papillary processes, that aggregate into a solid cluster. They are very vascular and grow out cluster above cluster until they reach large dimensions.
Diagnosis from Horse Pox. Since the days of Jenner the claim has been constantly made that grease and horse pox were one and the same. Horse pox is however to be distinguished by its transient course, its inoculability, its incubation of three days, its abundant exudate concreting on the hairs of the pastern as a yellow mass suggestive of crystalline structure, by the red pit in the skin in which this mass is imbedded, by the spontaneous recovery in about 15 days, and by the immunity on a subsequent inoculation. It is communicable to cattle and to man, producing the characteristic large umbilicated vesicle and scab.
Treatment. The first consideration is to remove the causes of local irritation and infection, give a clean sweet stall, with dry floor, and allow no contact with putrid liquids, mud, cold water, melting snow or other irritant. If exercise is needful to obviate stocking of the legs give it on dry clean ground.
If inflammation runs high with fever and costiveness a laxative will be valuable and it may be well to follow this in some cases with cooling diuretics. When the animal has been on a heavy grain ration this should be largely cut down in keeping with enforced idleness, or restricted work. If on the other hand condition is low, and the discharge profuse a more generous ration may be desirable.
Local treatment is essentially soothing and antiphlogistic, and in view of the infection should be antiseptic. White lotion (acetate of lead and sulphate of zinc of each ½ oz., water 1 quart) has been long used with fair success, for although lead sulphate is thrown down, it is in part freed again through contact with the exudate. It will be materially improved by the addition of 1 dr. carbolic acid, creolin, lysol or chloro-naphtholeum or by some other antiseptic. Lead acetate alone with an antiseptic is an excellent substitute. In mild cases the surface may be wet with the lotion several times a day: while in severe ones the lotion may be applied on a bandage kept constantly wet. When secretion is well established it may be better to use dry applications, as calomel; salicyclic acid 10 parts, with iodine 10 parts; calomel and lamp black; carbolated oxide of zinc or burned alum, salol, etc. After washing and drying the skin, dust this freely even into the deepest wrinkles and cover with cotton and bandage. Dress twice daily. For very fœtid cases, Robertson recommends zinc chloride 1 oz. in 1 qt. water with the addition of glycerine and phenol, and again a saturated solution of copper sulphate with carbolized glycerine. For profuse secretion after the subsidence of active inflammation Renal highly recommends wood tar with 5 to 10 drops of sulphuric acid to the ounce. Under these circumstances a powder of gloss starch 5 ozs. with iodine ½ oz. may be employed twice daily. Or again, 1 oz. each of carbolic acid, tincture of iodine and glycerine may be employed. When one agent seems to be losing effect, it is well to change for another and never to neglect the regular dressing, until full recovery has been secured.
In case of grapes the actual cautery is the most efficient measure. Heat a blacksmith’s fire shovel to a bright red and use this to cut through the pedicles, a cool shovel being kept constantly beneath it and in contact with the pedicles, so as to protect the adjacent skin from injury by the radiated heat. The lower shovel must be dipped in cold water at very frequent intervals to cool it and prevent cauterization of the skin between the pedicles. This not only removes the diseased and infected masses, but leaves the stumps of the pedicles aseptic. Another method is to cut off the “grapes” and staunch the blood with the actual cautery at a dull red heat. Still another is to tie the pedicle of each excrescence separately so as to cut off circulation and secure sloughing. This is, however, a long, tiresome process, and entails prolonged contact with much infecting dead tissue. After either method the parts must be dressed with antiseptics, and dealt with generally like cases in which the excrescences had not formed.