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 hypocalcemia(milkfever) or Parturient paresis in cow

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المساهمات : 73
تاريخ التسجيل : 29/07/2008
العمر : 36

مُساهمةموضوع: hypocalcemia(milkfever) or Parturient paresis in cow   السبت أغسطس 02, 2008 2:21 pm

Parturient paresis is an acute to peracute, afebrile, flaccid paralysis of mature dairy cows that occurs most commonly at or soon after parturition. It is manifest by changes in mentation, generalized paresis, and circulatory collapse.
Etiology:
At or near the time of parturition, the onset of lactation results in the sudden loss of calcium into milk. Serum calcium levels decline from a normal of 10-12 mg/dL to 2-7 mg/dL. Commonly, serum magnesium is increased, serum phosphorus is decreased, and cows are hyperglycemic. The disease may be seen in cows of any age but is most common in high-producing dairy cows >5 yr old. Incidence is higher in the Jersey breed.

Clinical Findings and Diagnosis:
Parturient paresis usually occurs within 72 hr of parturition. The disease can contribute to dystocia, uterine prolapse, retained fetal membranes, metritis, abomasal displacement, and mastitis.
There are 3 discernible stages of parturient paresis. During stage 1, animals are ambulatory but show signs of hypersensitivity and excitability. Cows may be mildly ataxic, have fine tremors over the flanks and triceps, and display ear twitching and head bobbing. Cows may appear restless, shuffling their rear feet and bellowing. If calcium therapy is not instituted, cows will likely progress to the second, more severe stage.
Cows in stage 2 are unable to stand but can maintain sternal recumbency. Cows are obtunded, anorectic, and have a dry muzzle, subnormal body temperature, and cold extremities. Auscultation reveals tachycardia and decreased intensity of heart sounds. Peripheral pulses are weak. Smooth muscle paralysis leads to GI stasis, which can be manifest as bloat, failure to defecate, and loss of anal sphincter tone. An inability to urinate may be manifest as a distended bladder on rectal examination. Cows often tuck their heads into their flanks, or if the head is extended, an S-shaped curve to the neck may be noted.
In stage 3, cows lose consciousness progressively to the point of coma. They are unable to maintain sternal recumbency, have compete muscle flaccidity, are unresponsive to stimuli, and can suffer severe bloat. As cardiac output worsens, heart rate can approach 120 bpm, and peripheral pulses may be undetectable. If untreated, cows in stage 3 may survive only a few hours.
Differential diagnoses include toxic mastitis, toxic metritis, other systemic toxic conditions, traumatic injury (eg, stifle injury, coxofemoral luxation, fractured pelvis, spinal compression), calving paralysis syndrome (damage to the L6 lumbar roots of sciatic and obturator nerves), or compartment syndrome. Some of these diseases, in addition to aspiration pneumonia, may also occur concurrently with parturient paresis or as complications. (See also problematic bovine sternal recumbency, Problematic Bovine Recumbency: Introduction.)

Treatment:
Treatment is directed toward restoring normal serum calcium levels as soon as possible to avoid muscular and nervous damage and recumbency. Recommended treatment is IV injection of a calcium gluconate salt, although SC and IP routes are also used. A general rule for dosing is 1 g calcium/45 kg (100 lb) body wt. Most solutions are available in single-dose, 500 mL bottles that contain 8-11 g calcium. In large, heavily lactating cows, a second bottle given SC may be helpful because it is thought to provide a prolonged release of calcium into the circulation. SC calcium treatment alone may not be adequately absorbed due to poor peripheral perfusion and should not be the sole route of therapy. No matter what route is used, strict asepsis should be employed to lessen the chance of infection at the injection site. Solutions containing formaldehyde or >25 g dextrose/500 mL are irritating if given SC. Many solutions contain phosphorus and magnesium in addition to calcium. Although administration of phosphorus and magnesium is not usually necessary in uncomplicated parturient paresis, detrimental effects of their use have not been reported. Magnesium may protect against myocardial irritation caused by the administration of calcium. Most products available to veterinarians contain phosphite salts as the source of phosphorus. However, phosphorus found in blood and tissues of cattle is primarily in the form of the phosphate anion. Because no pathway exists for the conversion of phosphite to the usable phosphate form, it is unlikely that these solutions are of any benefit in addressing hypophosphatemia.
Calcium is cardiotoxic; therefore, calcium-containing solutions should be administered slowly (10-20 min) while cardiac auscultation is performed. If severe dysrhythmias or bradycardia develop, administration should be stopped until the heart rhythm has returned to normal. Endotoxic animals are especially prone to dysrhythmias caused by IV calcium therapy.
Administration of oral calcium avoids the risks of cardiotoxic side effects and may be useful in mild cases of parturient paresis. Calcium propionate in propylene glycol gel or powdered calcium propionate (0.5 kg dissolved in 8-16 L water administered as a drench) is effective and avoids the potential for metabolic acidosis caused by calcium chloride. Oral administration of 50 g of soluble calcium results in ~4 g calcium being absorbed into the circulation.
Hypocalcemic cows typically respond to therapy immediately. Tremors are seen as neuromuscular function returns. Improved cardiac output results in stronger heart sounds and decreased heart rate. Return of smooth muscle function results in eructation, defecation, and urination once the cow rises. Approximately 75% of cows stand within 2 hr of treatment. Animals not responding by 4-8 hr should be reevaluated and re-treated if necessary. Of cows that respond initially, 25-30% relapse within 24-48 hr and require additional therapy. Incomplete milking has been advised to reduce the incidence of relapse. Historically, udder inflation has been used to reduce the secretion of milk and loss of calcium; however, the risk of introducing bacteria into the mammary gland is high.
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