Hypocalcemia

Basic Information

Definition

A demonstrable serum calcium level below the established reference range

Epidemiology

Species, Age, Sex

• Any species of bird may suffer from hypocalcemia. It is frequently reported in African grey parrots.

• Birds between 2 and 5 years may show increased susceptibility.

• Hypocalcemia is more common in egg-laying females

Genetics and Breed Predisposition

• African grey parrots

• Excessive egg-laying hens (e.g., cockatiels)

Risk Factors

• Low-calcium diet

• Vitamin D–deficient diet

• Excessive dietary vitamins A and E

• Excessive dietary phosphorus

• Indoor birds in an ultraviolet (UV)-deficient environment

• High–egg-producing birds

Associated Conditions and Disorders

• Nutritional secondary hyperparathyroidism

• Fibrous osteodystrophy

• Rickets

• Osteoporosis

• Pathologic fractures

• Chronic egg laying

Clinical Presentation

Disease Forms/Subtypes

• Hypocalcemia of African grey parrots

• Nutritional hypocalcemia

History, Chief Complaint

• Seizures

• Lethargy

• Weakness

• Production of noncalcified eggs

• Fractures

Physical Exam Findings

• Seizures

• Weakness

• Ataxia

• Poor feather condition

• Bone deformities

Hypocalcemia
Skeletal leg deformities caused by a nutritional calcium deficiency.

• Fractures

Etiology and Pathophysiology

• Calcium is an abundant body mineral, most of which is found in the bones. Ionized calcium, the metabolically active form, functions in coagulation, calcification of egg shells, muscle and nerve conduction, and parathyroid hormone regulation.

• Vitamin D₃ aids calcium absorption from the gastrointestinal tract through the synthesis of calcium-binding proteins. UVB light is necessary for conversion of vitamin D into the metabolically active form of vitamin D₃ (cholecalciferol). Studies have shown that when a D₃-deficient diet is fed, excessive quantities of vitamins A and E in the diet affect the utilization of vitamin D₃ negatively.

• A fall in plasma calcium stimulates the production of parathyroid hormone, a major function of which is to increase osteoclastic activity, thus mobilizing calcium from the bones and increasing blood plasma concentration. Nutritional secondary hyperparathyroidism leads to excessive mobilization of calcium. This resorbed bone is replaced by fibrous connective tissue, which can lead to deformities and pathologic fractures. Parathyroid hormone also increases the resorption of calcium in the kidneys, thereby decreasing urinary loss.

Diagnosis

Differential Diagnosis

• Hypoglycemia

• Neoplasia

• Heavy metal toxicity

• Organophosphate toxicity

• Infectious disease (viral, bacterial, fungal, or parasitic)

• Hepatic disease

• Renal disease

Initial Database

• Plasma chemistry panel: serum calcium is species specific, and reference ranges should be provided by the laboratory used. Reference ranges for African grey parrots of between 2.0 and 3.0 mmol/L have been observed in birds exhibiting clinical signs of hypocalcemia.

• Ionized calcium: sample reference ranges for African grey parrots are between 0.96 and 1.22 mmol/L.

• Whole-body radiographs can detect lack of cortical bone density.

Advanced or Confirmatory Testing

• 25-Hydroxycholecalciferol

• 1,25-Dihydroxycholecalciferol

• Parathyroid hormone

Treatment

Therapeutic Goals

• Correct clinical signs.

• Correct any husbandry issues contributing to hypocalcemia.

Acute General Treatment

• Calcium gluconate 10-100 mg/kg IM q 12 h prn

• Vitamin A, D, and E supplementation may be given if deficiencies are suspected.

Vital E-A + D (Schering Plough): 3300 IU/kg (1000 IU/300 g/BW) IM q 7 d prn

• Fluid therapy

• Stabilize pathologic fractures if present.

Chronic Treatment

• Oral calcium glubionate: 25 mg/kg q 24 h prn

• UVB supplementation

• Dietary changes

• Manage excessive egg laying.

Salpingectomy

Hormone therapy (see leuprolide acetate)

Drug Interactions

• Animals with cardiac or renal disease should be carefully monitored while receiving calcium therapy.

• Excessive amounts of vitamins A and D may cause hypercalcemia owing to increased mobilization of calcium from bones and gastrointestinal absorption.

Possible Complications

• Seizures

Regurgitation and aspiration

• Pathological fractures: birds with hypocalcemia should be handled cautiously

• Coma

• Death

Recommended Monitoring

Total calcium and ionized calcium

Prognosis and Outcome

Dependent on severity of clinical signs. Prognosis is poor if extensive remodeling of bones has taken place.

Pearls & Considerations

Comments

Chronic cases of hypocalcemia may achieve a normal plasma calcium concentration through compensating mechanisms. It is recommended to treat for hypocalcemia if clinical signs and history are strongly suggestive, despite a normal plasma calcium concentration.

Prevention

• Birds should be fed a good quality pelleted diet without excessive vitamin A and E supplementation.

• Birds that are provided a source of UVB light may be at lower risk for development of hypocalcemia.

Client Education

See Prevention.