Hypocalcaemia

In this post we'll learn about the pathogenesis, clinial signs and treatment of hypocalcaemia. 

 Hypocalcaemia is an abnormally low level of calcium in the blood plasma of an animal characterised by general muscle weakness, circulatory collapse and depression and unconsciousness. This condition is also known as milk fever or parturient paresis and commonly occurs at the time of lactation. 

Pathogenesis

There are several possible causes of hypocalcaemia in cattle. One of these is that there is excessive loss of calcium from colostrum beyond the capacity of absorption from the intestine and mobilisation of bones. This is because colostrum has about twice the amount of calcium as regular milk. 

At parturition there is also an impairment of the absorption of calcium from the intestines. This may be due to the dietary changes that a lactating cow experiences. In addition, the transport mechanism for the movement of calcium across the intestine, which is stimulated by Calcitriol, takes 16-24 hours to be activated. The amount of Calcitriol receptors in the intestine also decreases with age. 

Another possible cause is that the mobilisation of calcium from the bones may not be rapid enough to maintain normal plasma calcium levels. Parathyroid hormone (PTH) usually initiates the production of Calcitriol which initiates the resorption of bone, but this takes 48 hours to be full effective. In addition, older cows have fewer osteoclasts which are responsive to PTH’s actions. Also, about 10% of cows have delayed or insufficient production of Calcitriol.  

Other contributing factors to the incidence of hypocalcaemia are the levels of calcium and magnesium in the blood plasma. When the levels of magnesium are low, the production and secretion of PTH and Calcitriol is prevented and this results in low calcium levels. In addition, blood calcium levels fall more rapidly when potassium intake is high. Low calcium levels also cause the drainage of magnesium from the brain which results in hypomagnesaemia. Thus hypocalcaemia and hypomagnesaemia often occur at the same time. 

Clinical Signs

The clinical signs of hypocalcaemia occur in three stages:

Stage 1

•   A brief stage of excitement 
• Tetany 
•  Hypersensitivity 
• Muscle tremor of the head and limbs 
•  Animals declined to move 
• Grinding of teeth 
• Muscle tremors of hind limbs progressing to ataxia 
• Temperature may be normal or slightly elevated.

Stage 2

• Sternal recumbency 
• Unable to rise 
• Depression and anorexia 
• Head turned to flank and ‘S’ shaped bend in neck 
• Tetany of limbs has been replaced by flaccidity 
• Dry muzzle and eyes 
• Reduced ability to thermo regulate (temperature may be normal or below normal) 
• Dilation of pupils 
• GI stasis and bloat 
• Weak pulse, low venous pressure 
• Expiratory groans

Stage 3

• Animal in lateral recumbency and cannot sit up 
• Coma 
•   Depression of temperature 
• Low venous pressure, rapid pulse, barely audible heart sounds 
• Severe bloat 
• The cow may not survive more than a few hours

Treatment and Prevention

Treatment involves the administration of calcium borogluconate intravenously into the jugular vein. This should be done slowly to effect while monitoring the heart rate for arrhythmias. The cow should respond with the following signs: belching, muscle tremors, improved amplitude and pressure of pulse, increased heart sound intensity, faeces is passed and the animal urinates, and sweat beads appear on muscle. The risk of relapse can be reduced by administering more calcium salts subcutaneously over the ribs. Anti-inflammatory drugs may also be given to reduce muscle soreness.

The most effective prevention method is to feed the animals anionic salts.

That's all for now, see you next time :)