Hypocalcemia

in Small Ruminants Treatment and Control

Source: msdvetmanual.com

Overview

• 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.
• 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 <7.5 mg/dL. The sudden decrease in serum calcium levels causes hyperexcitability of the nervous system and reduced strength of muscle contractions, resulting in both tetany and paresis. Parturient paresis may be seen in cows of any age but is most common in high-producing dairy cows entering their third or later lactations. Incidence is higher in Channel Island breeds.

Clinical signs

• Parturient paresis usually occurs within 72 hr of parturition. It can contribute to dystocia, uterine prolapse, retained fetal membranes, metritis, abomasal displacement, and mastitis.
• Parturient paresis has three discernible stages. 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 manifest as bloat, failure to defecate, and loss of anal sphincter tone. An inability to urinate may 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 complete 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.

Diagnosis and differentials

• 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.

Treatment and control

• 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 of 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 alone may not be adequately absorbed because of poor peripheral perfusion and should not be the sole route of therapy.
• Plasma calcium levels for subclinical hypocalcemia are <8.0 mg/dL (<2.0 mmol/L)
• Calcium: 1 g Ca/45 kg of BW intravenous, response to therapy should be rapid (within 5–10 minutes).
  r Subcutaneous or oral calcium may be administered subsequently for a longer-acting effect in severe cases. Care must be taken to administer in small boluses (no more than
  50 mL per site) using clean technique or to ensure oral calcium is administered carefully or directly into the rumen (avoid calcium chloride boluses due to esophageal irritation).