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From the large animal clinic
Post mortem examination of experimental and clinical downer cows reveal similar lesions which are for the most part localized in the upper hind limb. This is because the upper parts of the hind limb are compressed against the pelvis while the more distal parts are positioned under the belly which is soft. While the abdomen is soft, it is also heavy and this weight on the common peroneal nerve can cause compression damage where the nerve crosses the stifle joint, especially the lateral surface of the head of the fibula1. For this reason, knuckling over on the fetlock, a sign of peroneal damage is often seen in recovered downer cows. This deficit is usually temporary, but it can be permanent.
Spinal trauma occurs usually as a result of riding other cows, being ridden by other cows, or by inadvertent trauma from farm implements. Other problems of the spine, such as lymphosarcoma tumors, or abscesses of the vertebrae will resemble spinal trauma. These cows may be able to stand weakly on their hind limbs. If they can, the hind limbs will usually knuckle over, especially at the fetlock. More often, they will be recumbent. Reflexes on the hind limbs are reduced. These cows can rarely be treated, and the prognosis is poor.
Calving paralysis is a commonly-used term to describe the paralysis of the hind legs which is seen in cows just after calving. It is caused by damage to the obturator nerve as the calf passes through the pelvic canal. This condition is most often seen after difficult calvings, the birth of large calves, or prolonged calvings. The cows are down, but alert and bright, usually eating. Most of these cows will recover with time and medical therapy.
If dystocia has occurred then calving paralysis may be a contributing factor as well. Calving paralysis is the preferred term for what is often referred to as obturator paralysis. Bilateral experimental transection of only the obturator nerves will not put a cow down unless the cow is on slippery concrete7. These cows will appear normal at a walk on dry concrete, but will spread the hocks wide when running. When they fall on dry concrete they can regain standing, but on a wet surface they have a hard time standing. The larger lumbar root of the sciatic nerve, as well as the obturator nerves, is vulnerable to compression damage between a fetus and the bony pelvic inlet portion of the birth canal. When both the lumbar root of the sciatic and the obturtator nerve are cut bilaterally, the experimental cow will be ataxic and not able to rise to a standing position in most cases.
Calving, Postfoaling, Paralysis
Description: Neurologic problems in downer cows following a calving are probably due to a combination of sciatic and obturator damage. Dx by signs of involvement of both nerves.
Fibular, Peroneal, Nerve Parasis, Paralysis
Description: Usually due to pressure on peroneal nerve while down, or trauma. If tibial nerve uninvolved can support at the hock. Could occur in any species, but most common in cattle following dystocia or being down for other reasons, and in small animals as a sequel to trauma, such as being hit by an automobile. Full weight can be taken on the limb, but there is knuckling of the fetlock. Skin sensation is lost on the dorsal tarsus and metatarsus.
Radial Nerve, Paresis, Paralysis
Description: Radial nerve innervates the extensors of the forelimb. Lesion of the lower motor neuron of the radial nerve leads to weakness or paralysis of the extensors, with flexion of the elbow, carpus and phalangeal joints. The leg is advanced with difficulty, and weight bearing is affected. Skin sensation is reduced on the dorsal metacarpus and phalanges.
Sciatic, Ischiatic, Nerve Paresis, Paralysis
Description: Could occur in any species but most common in cattle following calving and small animals following trauma. Occurs occasionally in all species following injection into the sciatic nerve, especially in small or young animals. In addition to knuckling the animal may show a dropped hock due to tibial nerve involvement. Skin sensation is affected in the entire limb with the exception of the area supplied by the saphenous nerve.
A controlled laboratory trial
Experimental induction of the downer cow condition has been used to study the effect of muscle and nerve compression in a controlled laboratory trial free of the numerous variables present in clinical cases3. Healthy non-pregnant cows were anesthetized with halothane anesthesia for 6, 9 and 12 hours to mimic the effects of recumbency in parturient paresis. All experimental cows were positioned on a hard rubber cow mat with the right hind limb under the body . Blood gases were monitored throughout the anesthetic period, and positive pressure ventilation with a mechanical respirator was used to maintain normal blood gases.
Within 30 minutes after the end point of anesthesia the cows were attempting to rise. Half (8 of 16) of the experimental subjects were able to rise within 3 hours after the end of anesthesia, but some of these showed temporary peroneal nerve paralysis on the previously down hind limb. Several cows which were not able to stand were able to rise on their forelimbs into an unusual bovine "dog sitting" position. All the others were able to stand on their forelimbs when lifted with clamps on the tuber coxae.