Calcium

Question 1

What are the main hormones involved in calcium homeostasis ?

Answer 1

• Parathyroid hormone (PTH)
• Vitamin D
• Calcitonin

Question 2

What are the role of PTH and target organs ?

Answer 2

PTH ↗︎ eC [Ca2+]
Target organs : bones and kidney

Question 3

What are the role of vitamin D and target organs ?

Answer 3

1,25(OH)2D or calcitriol (active form of Vitamin D) ↗︎ eC [Ca2+] (more delayed effect than PTH)
Target organs :
* bones
* kidney
* intestine
* ⊖ PTH

Question 4

From which organ Calcitonin is secreted ?
What are the role of Calcitonin and target organs ?

Answer 4

Calcitonin, from C-cells of thyroid gland, ↘︎ eC [Ca2+]
Main target organ : bone

Question 5

What are the main sources of Ca2+ excretion ?

Answer 5

• Renal (++)
• Feces
• Sweat (+)
• Milk (++)

Question 6

Which factor influences [Ca2+] ?

Answer 6

pH
* Acidemia = ↗︎ Ca2+
* Alkalosis = ↘︎ Ca2+

Question 7

Which factor influences [total Ca] ?

Answer 7

Albumin
Hypo-albuminemia = ↘︎ tCa → pseudo-hypocalcemia
Hyper-proteinemia = ↗︎ tCa

Question 8

What are the clinical signs of hypercalcemia ?

Answer 8

Horses are very tolerant to hypercalcemia. Clinical signs are often due to the primary disease.
Severe cases (poor prognosis) → neuro. signs, muscle weakness, constipation, polyuria

Question 9

DDX of hypercalcemia

Answer 9

1- Renal failure (acute and chronic) : ↗︎ Ca and ↘︎ P
2- Hypercalcemia of malignancy : ↗︎ PTHrP → pseudohyperparathyroidism or paraneoplastic syndrome
3- Vitamin D toxicosis (plants) : ↗︎ Ca and ↘︎ P
4- Primary hyperparathyroidism : parathyroid adenoma
5- Hypercalcemia in foals : with asphyxia

Question 10

What to do with hypercalcemia ?

Answer 10

1- Re-check tCa and Ca2+
2- Evaluate renal function
3- Measure [P]
4- Measure [PTH]
5- Measure vitamin D metabolites

Question 11

What to do with hypocalcemia ?

Answer 11

1- Re-check tCa and Ca2+
2- Measure [albumin]
3- Evaluate clinical signs
4- Measure [PTH]

Question 12

TT of hypercalcemia ?

Answer 12

1- Decrease Calcium intake : diet (grass hay rather than alfalfa)
2- Increase renal excretion : fluidotherapy +/- furosemide

Question 13

Clinical signs of hypocalcemia ?

Answer 13

Depression, tachycardia, tachypnea, profuse sweating, muscle fasciculation, synchronous diaphragmatic flutter

Question 14

DDX of synchronous diaphragmatic flutter

Answer 14

• Hypocalcemia
• Hypochloremic metabolic alkalosis
• Hypokalemia

Question 15

DDx of hypocalcemia ?

Answer 15

• Colic : strangulating intestinal lesion
• Acute diarrhea : hypoCa, hypoMg, hyperP, acidosis
• Endotoxemia
• Lactation tetany : rare, during first week of lactation
• Nutritional secondary hyperparathydoidism : due to low Ca or high P in the diet → osteodystrophia fibrosa
• Exhaustion syndrome in exercising horses : loss of Ca2+, K+ and Cl- in sweat → synchronous diaphragmatic flutter
• Cantharidin toxicosis
• Primary hypoparathydoidism (rare) : low Ca with low PTH

Question 16

What is the most important cause of hypocalcemia in foals ?

Answer 16

Sepsis

Question 17

TT of hypocalcemia ?

Answer 17

Fluid therapy : calcium borogluconate
Many hypoCa horses are also hypoMg → both supplementation

Question 18

What are the recommendation for Ca/P ratio diet ?

Answer 18

Ca/P ≧ 2/1