Physiology of Hypocalcaemia

Question 1

• What disorders can cause hypocalcaemia?

Answer 1

Pseudohypocalcaemia, parturient paresis (milk fever), thumps (endurance horses), eclampsia (dogs) & metabolic bone disease (reptiles & birds)

Question 2

• What causes pseudohypocalcaemia?

Answer 2

Hypoalbuminaemia (albumin is the main calcium binding protein) caused by colitis, malabsorption, renal failure or liver failure

Question 3

• What are the main causes of hypocalcaemia in horses?

Answer 3

Sweating, milk production & diarrhoea

Question 4

• What are the main effects of hypocalcaemia?

Answer 4

Increased neuromuscular irritability, decreased smooth muscle contraction, decreased skeletal muscle contract, reduced cardiac muscle contractility

Question 5

• What is parturient paresis?

Answer 5

Milk fever characterised by a drop in plasma calcium levels, normal range is 2.2-2.6 mmol/L, milk fever is usually present in the range 0.75-1.5 mmol/L

Question 6

• What are the three stages of parturient paresis?

Answer 6

Stage 1 – hyperexcitability (1.37-1.87 mmol/L)
Stage 2 – recumbent, but still sternal (0.87-1.62 mmol/L)
Stage 3 – lateral recumbency/ unconscious (0.50-0.87 mmol/L)

Question 7

• What are the fast, moderate and slow sources of calcium?

Answer 7

Fast – blood, reabsorbed calcium from urine, calcium from bone fluid
Moderate – calcium from intestine
Slow – calcium from bone matrix

Question 8

• What does hypomagnesaemia inhibit?

Answer 8

PTH release & calcium absorption in the intestine