Spastic paresis is a progressive unilateral or bilateral hyperextension of the hindlimb(s). It is seen sporadically in most breeds of cattle. Post-legged cattle are most frequently affected. Attempts to move are believed to simultaneously trigger contractions of both extensors and flexors of the limb. Spastic paresis is currently considered to be inherited via a recessive gene(s) with incomplete penetrance.
The disease may be seen within the first 6 mo of life. As the animal ages, the gastrocnemius muscles gradually contract. The hock and stifle become increasingly extended. Over a period of months, the hindlimbs become so stiff that the animal walks with short, pendulum-like steps. If only one limb is affected, the animal stands with the affected limb camped back and the sound limb held toward the midline to maintain balance. If both hindlimbs are affected, the animal may attempt to bear more weight on the forelimbs by holding them well back and simultaneously arching its back.
The quadriceps muscle has been implicated in the pathology of this disorder and can be distinguished from the form of the disorder affecting the gastrocnemius through use of a femoral nerve block.
There is no successful medical treatment. Because spastic paresis is heritable, affected animals (especially breeding bulls) should be eliminated from the herd. Palliative surgical treatment may be attempted, although ethical issues should be considered when breeding stock is involved. The procedures, usually performed on calves, include complete tenotomy of the gastrocnemius tendon, which results in a dropped hock; complete tibial neurectomy, which results in sufficient relief to permit a steer to be finished for slaughter; and partial tenectomy of the two insertions of the gastrocnemius muscle and the calcanean tendon sheath, which overcomes the problem of the dropped hock.