SHIVERING "Shivering"is a nervous affection char acterized by spasmodic movements of certain groups of muscles, notably those of the hind limbs and the tail, although in certain cases those of the fore limbs or even of the face or trunk may be involved.
The cause is believed to be a slowly progress ive sclerosis of the spinal cord with increase of connective tissue and diminution of nervous elements, together with lack of vascularity. Heredity in all probability plays some part in the production of the disease.
In some instances"shivering"appears to arise as a sequel to some antecedent constitu tional disease, as strangles, pneumonia, or influ enza, in which toxins may be produced, which may in certain cases affect the spinal cord, though sometimes"shivering"does not make its appearance until some years after the primary disease has disappeared. The con nection between the two conditions is often somewhat vague and open to doubt.
The disease occurs in all classes of horse, of all ages, but is probably least common among ponies, particularly among ponies bred under natural conditions upon moorland. It would thus appear to be induced by domestication.
The symptoms of shivering are quite charac teristic when marked, although they may be very hard to detect or even unnoticeable when only very slight. As a rule, nothing unusual can be detected whilst the animal is standing still, as when feeding in the stable. In a well marked case the symptoms are exhibited im mediately the animal is moved, or perhaps only during the first few steps, when he is turned over in the stall, and particularly when he is forced to back, a movement accomplished with difficulty. Some horses only show symptoms after foot injury, as after being"pricked"during shoeing, or when dermatitis exists below the hock (grease, cracked heels, etc.), or when symbiotes are present. Possibly the latter instances are not true examples of the disease, but nevertheless symptoms identical with"shivering"are manifested under these circum stances in certain animals.
When the spasms are excited by any of these stimuli, the hind foot is suddenly jerked from the ground and the limb is held suspended in mid-air in a position of abduction, quivering violently, whilst in more severe cases the inter mittent spasmodic movements may be so pro nounced that the horse is only able to retain his balance by performing hopping movements with the other limb. At the same time the tail
is elevated and trembles rapidly, whilst in occasional instances other groups of muscles become involved, as those of the face, ears, and even those of the trunk. The symptoms become very aggravated if any injury to the lower por tion of the limb should occur. Attacks of colic, catarrh, etc., also appear to render the symp toms more severe, and during the course of the illness the horse may be unwilling or unable to lie down and may be incapable of again getting on his feet should he do so. Some"sbiverers" always sleep standing, and accordingly may suffer from chronic contusions of the fetlocks from knuckling whilst at rest.
When a fore limb is affected the leg is first abducted and then carried forwards, quivering the whole time. Sometimes the muscles of the lips, eyelids, and ears are involved alone or in company with one of the limbs. The commis sure of the lips is retracted, the eyelids flicker, and the ears quiver.
In very slight cases involving the limbs de tection is often very difficult and is of consider able importance, if only as regards examination for soundness.
Backing the animal or turning him in either direction in narrow circles may be sufficient to reveal the existence of the disease, but in very mild cases more severe tests may be necessary. Lifting or hammering the hind feet, particularly whilst the horse is resting after exercise, or pricking the coronet may reveal symptoms of the disorder.
Shivering usually shows a tendency to become worse with work and to improve after a rest. Its appearance may occasionally be quite sudden, but usually it develops very slowly. Hunters may jump well one season but the next may have difficulty in lifting the hind limbs over an obstacle. Gradually the posterior extremities become stiff and the muscles undergo atrophy, so that the animal is unable to do the work required of him. He shows no inclination to lie down, or if by any chance he does assume the recumbent position, he is found down in the morning and unable to rise, though he will usually succeed in doing so if rolled over on to the opposite side. Some shiverers, however, work for years without showing any marked inability to perform their tasks.
Treatment is quite useless.