Bovine
Milk fever
Cows, especially older, higher producing dairy cows are most often affected.
Milk fever is a condition of older, third to sixth lactation, high-producing dairy cows. It is associated with parturition, usually within 72 hours of giving birth. Because of the high volume of milk produced during this time, and subsequent demand for calcium, these cows often develop hypocalcemia, or abnormally low levels of calcium in the blood. Since calcium is required for the release of acetylcholine at the neuromuscular junction, affected animals will begin to experience muscle weakness. As this hypocalcemia worsens, the cow will become too weak to stand and will eventually become comatose over a matter of hours.
The hypocalcemia of bovine postparturient paresis is treated intravenously with calcium gluconate. Affected cows have an excellent prognosis if treated early and properly. However, the worse the symptoms, the worse the prognosis tends to be. Milk fever may be prevented with appropriate feeding or calcium or vitamin D supplementation during the weeks preceding parturition.
Initial signs include excitability, hypersensitivity and restlessness. Tachycardia and mild hyperthermia are commonly associated with tetany in the early stages. Subsequently gradual, worsening muscular weakness begins that progresses into sternal then lateral recumbency. Gastrointestinal atony predisposes to constipation and mild bloating. As calcium levels decrease other signs may include weak pulses, poor pupillary light response, flaccid paralysis, severe bloating, and coma.
A weak, trembling cow is first seen. Localized spasmodic muscle contractions may cause a mild increase in body temperature. The heart rate is often elevated. The heart rate remains elevated but the temperature declines with progression. In advanced stages the most common symptom is a "downer" cow that is usually unable to rise when stimulated. An affected cow will often have its head turned into its flank. If left untreated the cow will lie down on her side and stretch out, thus predisposing her to bloat. The cow will become progressively more depressed until she is unresponsive and comatose, with dilated, unresponsive pupils.
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.
An older dairy cow near calving or that has recently calved that shows clinical signs and symptoms is highly diagnostic. Serum calcium levels will reveal hypocalcemia, or low blood calcium. However, because of the rapid nature of this illness and the often slow return of laboratory results, treatment is usually initiated based on clinical signs only.
The prognosis is excellent if cows are treated early and properly. As the symptoms worsen so does the prognosis. Cows down for more than 48 hours may develop muscle inflammation and never be able to stand. Relapse is relatively common unless longer acting supplements are added to the treatment plan. Older cows and cows displaying signs prior to calving have the highest risk for relapse.
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.
Early intravenous calcium gluconate is the treatment of choice for severely affected patients. The solution must be given slowly because rapid calcium infusion may result in cardiac arrest. Concurrent use of subcutaneous calcium gluconate may prevent recurrence, by slow release of biologically available calcium from the tissues into the bloodstream. Patients with mild signs are appropriately treated with subcutaneous, intraperitoneal, and/or oral calcium products.
The response to properly administered calcium therapy is quite characteristic. The cow's symptoms will appear to reverse themselves as they had previously progressed. The laterally recumbent cow will sit up to sternal position, then it will often begin to have tremors over its body. As all bodily functions affected by hypocalcemia begin to reverse, the affected animal may urinate, belch, and then begin the wobbly effort to rise. Cows generally rise within one hour. Repeat treatment may be necessary in 12 hours if the cow is still unable to rise.
Milk fever may be prevented with appropriate feeding during the weeks leading up to parturition. During this "dry-off" period, the cow's dietary intake of calcium should be lower than when the cow is producing milk. The resulting lower blood calcium level stimulates production of parathyroid hormone, or PTH. PTH stimulates the cow's body to quickly increase blood-calcium levels from calcium stored in the bones. However, PTH is slow to synthesize in the face of a rapid calcium decline. Essentially, lower dietary calcium during the dry-off period keeps the cow's PTH at a level that will meet any sudden calcium demand.
Another important preventive measure is dietary acidification through reduction of the dietary cation-anion difference (DCAD). Diets can be adjusted for the portion of the herd that is near parturition, using urine pH to monitor the cows' acid-base status. Prophylactic calcium treatment of cows near to or immediately after, calving may lower the incidence of milk fever in a herd. Vitamin D supplementation before calving will increase calcium absorption through the intestines, and is sometimes recommended to prevent milk fever. |
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