Hypovitaminosis D in Veterinary Medicine

Vocabulary terms and definitions covering the mechanisms, clinical signs, diagnosis, and treatment of Hypovitaminosis D in veterinary patients.

Hypovitaminosis D

inadequate vitamin D , commonly by insufficient dietary intake in dogs/cats or secondary to gastrointestinal malabsorption, liver disease, or kidney disease.

Reduced intestinal calcium absorption

VD promotes calcium absorption from intestine by increasing calcium binding proteins and active transport in intestinal mucosa.

Low VD - reduced intestinal calcium absorption

Dietary calcium passes through GI tract unabsorbed, blood calcium level fall.

Reduction in Calcium absorption earliest primary effect of VD defiency

Parathyroid hormone compensation (Secondary hyperparathyroidism)

Decrease in serum calcium stimulates parathyroid glands to release parathyroid hormone (PTH), PTH:

• Increases bone resorption, releasing Ca and P from bone matrix

• Increases renal tubular calcium reabsorption, reducing Ca loss in urine

A compensatory increase in parathyroid hormone ($PTH$) release to restore blood calcium levels by increasing bone resorption and renal calcium reabsorption at the expense of bone integrity.

Bone resorption

The process where parathyroid hormone stimulates the release of calcium and phosphate from the bone matrix into the bloodstream.

Renal tubular calcium reabsorption

The action of parathyroid hormone on the kidneys to reduce the amount of calcium lost in the urine.

Calcitriol

The active form of vitamin D; its synthesis is stimulated by parathyroid hormone and is essential for intestinal calcium handling.

Hypophosphataemia

Reduced blood phosphate levels caused by low intestinal absorption and increased renal loss due to elevated parathyroid hormone levels.

Osteomalacia

A consequence of insufficient calcium-phosphate availability for normal bone mineralisation occurring in adult animals.

Rickets

A consequence of insufficient calcium-phosphate availability for normal bone mineralisation occurring in juvenile animals.

Pathological fractures

Bone breaks that occur due to weakened bone density and impaired mineralisation rather than significant trauma.

Hypocalcaemia

Low blood calcium levels which may manifest clinically as muscle weakness or tremors.

25-hydroxyvitamin D

The serum component measured in blood tests to diagnose vitamin D deficiency; it serves as the precursor to active calcitriol.

Clinical signs

• Bone pain or lameness

• Pathological fractures

• Poor skeletal development or deformities in juveniles

• Muscle weakness or tremors associated with hypocalcaemia

• Reduced bone density on radiographs

Radiographic evidence

Diagnostic findings from X-rays showing reduced bone density or skeletal abnormalities associated with vitamin D deficiency.

Diagnosis

• Blood tests showing low or low-normal calcium

• Reduced phosphate levels

• Elevated parathyroid hormone concentrations

• Low serum 25-hydroxyvitamin D

• Radiographic evidence of reduced bone density or skeletal abnormalities

Treatment

• Vitamin D supplementation

• Correction of underlying causes such as dietary imbalance or gastrointestinal disease

• Calcium supplementation where indicated

• Careful monitoring to avoid hypercalcaemia during treatment