Avian hypocalcemia and nutritional secondary hyperparathyroidism

Doses on this pageEvery dose below is quoted from the cited source. Verify against the current label/formulary and the patient's full clinical picture.

Causes and birds at risk

LafeberVet's avian calcium page names three routes to calcium deficiency. These are inadequate dietary calcium, excess dietary phosphorus, and inadequate vitamin D [3]. The page notes that in seed-eating birds, all-seed diets supply too much phosphorus and too little calcium. For carnivorous birds, muscle or organ meat fed without bone is the calcium-deficient equivalent [3].

The Merck Veterinary Manual says seed-based diets are well known for both a calcium-to-phosphorus imbalance and amino acid deficiencies [1]. It singles out sunflower seeds, which many parrots choose first, as low in calcium and high in fat. It also notes that safflower seeds carry more fat than sunflower seeds and are likewise short on calcium [1]. A separate Merck chapter on psittacine nutrition states that strictly seed diets are suboptimal "regardless of supplementation," because seeds lack vitamin A, protein and calcium, among other nutrients [2].

Vitamin D status adds to the dietary picture. The Merck Veterinary Manual says the effect of a low-calcium diet is often compounded when indoor birds get too little unfiltered sunlight, which leads to vitamin D3 deficiency as well [1]. The psittacine nutrition chapter adds a second dietary route. It says that allowing "cafeteria-style" feeding results in unbalanced dietary consumption [2].

According to the Merck Veterinary Manual, nutritional secondary hyperparathyroidism can occur in both young and older birds [1]. The source names African grey parrots as especially affected [1]. LafeberVet adds that chronic egg laying is "an important drain on calcium stores" in parrots [3].

Clinical signs

The Merck Veterinary Manual lists the following clinical signs [1]:

• weakness
• ataxia
• tremors
• depression
• seizures
• pathologic fractures

In young birds, the manual says hypocalcemia may show as osteodystrophy, with curved and deformed long bones and vertebrae, particularly in African grey parrots [1]. LafeberVet describes several skeletal changes in growing birds with profound deficiency. These include lameness, rickets, dyschondroplasia and enlarged, painful joints [3]. The page adds that adult birds can develop an osteoporosis-like condition. In that condition, weakened bones deform or fracture under the bird's own weight or the pull of its muscles [3].

In breeding birds, the Merck Veterinary Manual reports several signs of calcium deficiency [1]:

• thin-shelled eggs
• reduced egg production and hatchability
• embryonic death
• cessation of laying
• egg binding
• cloacal prolapse

For the grey parrot hypocalcemic syndrome, LafeberVet lists weakness, ataxia, falling off the perch and seizures. The page notes that these signs respond to calcium administration [3]. It describes the syndrome as frequently diagnosed in young birds, especially those on all-seed diets. Its cause is unknown, and the page says it "may be related to an inability to effectively mobilize calcium from bone" [3].

Diagnosis

According to the Merck Veterinary Manual, diagnosis rests on history and physical examination. The typical history is "a sedentary bird on a poor diet" [1]. The manual lists the supporting findings that may be present:

• decreased plasma and ionized calcium
• increased phosphorus
• decreased vitamin D, measured as 25-hydroxycholecalciferol
• reduced bone density and/or pathologic fractures on radiographs [1]

Testing pitfalls

Reproductive status affects serum calcium values. LafeberVet explains that laying hens mobilize medullary bone and eat calcium-rich foods. Together, these produce a physiologic hypercalcemia. The page gives serum calcium of 8-10 mg/dL for non-laying hens and 15-30 mg/dL for healthy layers [3]. The cited sources do not give ionized calcium reference intervals for any species.

Classification

None of the cited sources provides a staging or grading system for avian hypocalcemia or nutritional secondary hyperparathyroidism. The Merck Veterinary Manual separates the developmental form in young birds, which presents as osteodystrophy, from the acute hypocalcemia syndrome in grey parrots [1]. LafeberVet describes a third presentation, the osteoporosis-like condition in adults [3].

Treatment described in the sources

The Merck Veterinary Manual lists four parts to treatment. These are supportive care, calcium supplementation, vitamin D supplementation, and conversion to an appropriate diet [1]. It states that "Initial treatment should consist of 10% calcium gluconate (100 mg/kg, IM)" [1]. The cited sources give no repeat interval, oral calcium dose or vitamin D3 dose for treatment.

When pathologic fractures are present, the manual says splinting or bandaging may be needed. It also lists cage rest, NSAIDs or analgesics [1]. The manual adds that the cage may need changes to limit climbing and reduce the chance of falls [1].

For the grey parrot syndrome, LafeberVet describes gradual conversion to a healthy diet. It adds that UVB exposure in the 285 to 315 nm range "may also promote normal calcium levels" [3]. The Merck pet bird chapter reports that most birds benefit from vitamin D3 given both orally and through UVB. It adds that grey parrots have been reported to rely more on UVB light than Amazona species to keep serum calcium adequate [1]. The sources do not give the study design or sample size behind that comparison. LafeberVet's reference list includes a 2006 Veterinary Record paper by Stanford on UVB and calcium metabolism in psittacine birds [3]. The cited pages do not summarize its methods.

The Merck Veterinary Manual describes long-term treatment and control as reducing reproductive activity through several measures [1]:

• diet conversion
• a shorter photoperiod
• removal of nest boxes
• removal of mates or perceived mates

The manual adds that leuprolide acetate and deslorelin implants can suppress the reproductive cycle temporarily and reversibly [1].

Oversupplementation risks

LafeberVet notes that in the avian species studied, harmful calcium levels sit only slightly above required levels. It warns that prolonged hypercalcemia can lead to nephrosis and soft tissue mineralization [3]. The Merck Veterinary Manual says excess oral calcium is generally not thought to cause clinical problems. Excess oral vitamin D3, however, can cause calcium accumulation in the kidneys and other tissues [1].

The psittacine nutrition chapter names macaws as sensitive to dietary vitamin D. In these birds, excess vitamin D can cause soft tissue calcification and renal failure [2]. The chapter states that toxic dietary levels for psittacines "have not been established." It notes that potentially toxic levels for poultry begin at 5,000 IU/kg of feed, though some studies suggest up to 40,000 IU/kg may be safe [2].

Prevention, diet and UVB

The Merck psittacine chapter estimates that, without natural sunlight, the minimum oral vitamin D requirement for grey parrots is likely to be 500-1,000 IU/kg [2]. It adds that how much vitamin D wild parrots obtain from food or sunlight is unknown [2].

LafeberVet's guidance on dietary calcium includes the following values [3]:

The page names dark, leafy greens and cooked egg with the shell as good calcium sources for pet birds [3]. It cautions that oxalate or phytate binding often limits how much calcium can be absorbed from plants. It also describes invertebrates and grains as generally poor sources [3].

The Merck Veterinary Manual ties exercise to bone strength. It notes that weight-bearing activity can lower fracture risk by improving balance and strength [1]. It also reports that essential fatty acids reduced fracture incidence and severity and increased bone density in poultry [1]. That evidence comes from poultry, not pet birds.

On housing, the manual describes an outdoor cage with direct sunlight and room to climb or fly. It suggests indoor UV lights where natural sunlight is not an option [1]. The manual cautions that birds outdoors need close watching, because predators can injure them through cage bars [1].

Client communication

The sources raise several points relevant to client discussions.

• Diet. The Merck pet bird chapter notes the difference between what owners offer and what birds actually eat. Owners may put out table foods, pellets and vegetables while the bird mostly eats seed [1]. It also notes that vitamin and mineral supplements added to drinking water tend to be unpalatable and ineffective, and can reduce water intake and cause dehydration [1].
• Sunlight. According to the psittacine chapter, owners often assume, wrongly, that sunlight through glass provides UVB [2]. The chapter adds that UVB is weaker farther from the equator, especially from late autumn to early spring [2].
• Lighting and heat. The same chapter says owners should be encouraged to provide direct sunlight, with cautions about heat, or properly used UVB bulbs [2].
• Prognosis. The cited sources do not address prognosis, recurrence rates or recheck intervals.

Before using any dose aboveVerify against the current label/formulary and the patient's full clinical picture.