21/06/2021
Milk fever in Cow (Hypocalcemia or Parturient paresis):
========
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.
1. Etiology:
Dairy cows will secrete 20–30 g of calcium in the production of colostrum and milk in the early stages of lactation. This secretion of calcium causes serum calcium levels to decline from a normal of 8.5–10 mg/dL to 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. Magnesium is also necessary for appropriate parathyroid hormone (PTH) secretion and activity in response to hypocalcemia. 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 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 adverse effects and may be useful in mild cases of parturient paresis; however, it is not recommended as the sole approach for clinical milk fever cases.
Products containing calcium chloride are effective but can be caustic to oral and pharyngeal tissues, especially if used repeatedly.
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, less injurious to tissues, avoids the potential for metabolic acidosis caused by calcium chloride, and supplies the gluconeogenic precursor propionate. Oral administration of 50 g of soluble calcium results in ~4 g of calcium being absorbed into the circulation.
Regardless of the source of oral calcium, it is important to note that cows with hypocalcemia often have poor swallowing and gag reflexes.
Care must be exercised during administration of calcium-containing solutions to avoid aspiration pneumonia. Gels containing calcium chloride should not be administered to cows unable to swallow.
Hypocalcemic cows typically respond to IV calcium 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 retreated 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.
5. Prevention:
Historically, prevention of parturient paresis has been approached by feeding low-calcium diets during the dry period. The negative calcium balance results in a minor decline in blood calcium concentrations.
This stimulates PTH secretion, which in turn stimulates bone resorption and renal production of 1,25 dihydroxyvitamin D. Increased 1,25 dihydroxyvitamin D increases bone calcium release and increases the efficiency of intestinal calcium absorption.
Although mobilization of calcium is enhanced, it is now known that feeding low-calcium diets is not as effective as initially believed.
Furthermore, on most dairy farms today, it is difficult to formulate diets low enough in calcium (
