The role of pressure damage in pathogenesis of the downer cow syndrome.

Experimental downer cows were produced by maintaining healthy cows in sternal recumbency for 6, 9, or 12 hours with the right pelvic limb positioned under the body. Halothane anesthesia was used to create this artificial parturient paresis-like position. In 8 of 16 experiments, cows were able to stand within 3 hours after anesthesia, but the others remained recumbent until death or euthanasia. There was no correlation between duration of the treatment and ability to stand after enforced recumbency. The appearance of the right pelvic limb of downer cows resembled the injured limbs of human patients with compartmental/crush syndrome, as well as the limbs of clinical downer cows. The affected limbs were swollen and held in rigid extension. Some animals which were able to stand also had swollen right pelvic limbs. Systemic signs of crush syndrome included dark yellow or brown urine suggestive of myoglobinuria, and marked elevation of serum creatine kinase enzyme levels. Highest creatine kinase levels were observed at 24 hours in the ambulatory group and at 48 hours in the downer group. Necropsy of downer animals revealed ischemic necrosis of the caudal thigh muscles and inflammation of the sciatic nerve caudal to the proximal end of the femur. Evidence of peroneal nerve damage was observed in at least 9 animals.