Bovine Postparturient Paresis - contd.
Postparturient paresis, or severe muscle weakness in cows resulting from hypocalcemia, occurs in older, third to sixth lactation, high-producing dairy cows that are near calving or have recently calved. It is characterized by progressive muscle weakness and depression that progresses into coma if not treated promptly.
Calving causes a high volume of milk production, and with it, a high demand for calcium from the cow's body. If the body is unable to respond quickly to this demand, the cow develops hypocalcemia, or an abnormally low blood-calcium level. Calcium is critically important to normal nerve and muscle function. Acetylcholine, a neurotransmitter substance acting at the neuromuscular junction, requires calcium to properly stimulate muscle movement. Hypocalcemic cows will begin trembling, and as the calcium level continues to plummet, will no longer be able to stand. Subsequently the cow becomes recumbent, first in the sternal position, and then laterally. Milk fever is one of a number of conditions that leads to a "downer" cow.
Postparturient paresis is favorable to early treatment with intravenous calcium supplementation. Delayed treatment may result in a comatose animal with a much poorer prognosis. Left untreated most patients will die.
As with most illnesses prevention is the key. Dietary calcium levels should be lowered in the weeks leading up to calving. This stimulates the cow to produce parathyroid hormone, which is necessary for quickly increasing blood calcium from calcium stored in the bones.
