The degree of contraction as well as its import varies in different subjects and in the various tendons which may be affected. Contraction is a slow-going process that is progressive, gradually causing a decrease in the length of the affected structure and eventually rendering the animal useless.
The practice of applying shoes with extended toe-calks for the purpose of "stretching" contracted deep digital flexor tendons (flexor pedis perforans) cannot be too strongly condemned. While the addition of an extension such as is ordinarily employed to the toe of a shoe of this kind, prevents for a time, frequent stumbling in such cases, the increased tensile strain which is thus occasioned hastens further contraction and subjects animals so shod to much unnecessary pain.
AFFECTIONS OF NERVES.
Because of their being protected by other structures, nerve trunks, which supply muscles of locomotion, are not subjected to frequent injuries such as contusions. However, they do become injured at times and the result is lameness, more or less severe.
Lameness originating from nerve affection, may involve central structures as, for example, the spinal cord, medulla oblongata or parts of the brain. In making an examination of some lame animals it is necessary to distinguish between cases of lameness that are of central origin and marked by incoördination of movement, and disturbances caused by other affections. Tetanus in its incipiency should not be confused with laminitis involving all four feet, or with certain forms of pleuritis, when careful examination is made, yet, in a way, to one not trained, the clinical symptoms are similar.
Disturbances of nerve function are caused in a variety of ways. It is not within the scope of this work to discuss central nervous disturbances caused by ingestion of mouldy provender, or disturbances of the brain or cord occasioned by infectious diseases, but mention of the existence of such conditions is appropriate.
By direct injury the result of blows, certain nerves are injured and muscles supplied by such nerves are rendered inactive. Depending upon the nature and extent of an injury thus inflicted, so the manner in which the affection is manifested varies. The suprascapular nerve is rather frequently injured causing partial or complete loss of function of the structures supplied by this nerve, and abduction of the scapulohumeral joint naturally results.
In some cases of dystocia the obturator nerve, (or nerves, if the involvement is bilateral), becomes injured by being caught between the maternal pelvis and some dense part of the fetus. This results in paralysis of the adductors of the thigh if sufficient injury is done.
It is said that nerves become over-stretched and held tense, in certain positions in which animals are obliged to remain while cast in confinement such as in some instances where unusual methods of restraint are employed. When the fore feet are drawn backward in such manner that great strain is put upon the radial nerve, it suffers more or less injury, and this is followed by partial or complete paralysis which may be temporary or permanent.
Degenerative changes affecting nerves, as in other tissues, occur and more or less locomotory impediment will follow—this depending upon the nerve or nerves affected and the nature of such involvement. Tumors may surround nerves and eventually the nerve so exposed becomes implicated in the destructive process. Before degenerative changes take place in the nerve substance, in such cases, pressure may completely paralyze a nerve when it is so situated. Melanotic tumors in the paraproctal tissue in some cases, because of the large size of the new-growths, cause paralysis of the sciatic nerve. The author has seen one case of brachial paralysis occasioned by an enormous development of fibrous tissue involving the structures about the ulna.