Hypocalcaemia in dairy cattle re-edited

(Source: http://www.eyefetch.com/image.aspx?ID=405372)
in dairy cattle
Sophie Rosevear, Jessie Neal, Tara Hall and Alex Doddridge
Calcium is essential, it is involved in many physiological processes
Dairy cows have been heavily selected for the ability to produce high milk
There is a fine calcium balance in the dairy cow
When demand for energy and calcium suddenly increases this balance
can be disrupted
Calcium homeostasis fails = milk fever (also called periparturient paresis)
Affects productivity and longevity of high producing dairy cows
The calcium balance
(Source: Horst 1986)
Calcium homeostasis
Failure of homeostasis and
development of hypocalcaemia
• Lactation generates a sudden, very high demand on calcium homeostasis
• Can result in an imbalance between calcium output and influx of calcium to
maintain the extracellular pool (plasma) from bone, kidney and intestine
• Failure of calcium homeostasis
• Between 5 and 20% of cows will develop milk fever
• Occurs within 12 to 24 hours of parturition
• Milk fever is hypocalcaemia severe enough to present clinical signs, when
plasma calcium levels are between 8 mg/dL and 6 mg/dL
Clinical Signs
(Source: http://informedfarmers.com/dairy-cattle-industry/downer-cow/)
Hyper excitability with anorexia, listlessness and muscle weakness
Body temperature declines as condition worsens
Sternal recumbency with lateral neck kink (as shown above)
Ruminal atony and constipation due to a loss of smooth muscle contractile function causing bloat
‘Crush syndrome’ followed by 'downer cow’ syndrome
If parturient birthing process is suspended
Weak heart sounds and tachycardia
Later stages cow is laterally recumbent with a temperature as low as 32°C (normal temp 38-38.5°C)
Death can occur in a few to several hours, and is likely at a rate of 60-70% without treatment
Predisposing factors
Most common in cows in 3rd lactation and older
Studies showing that the intestinal receptors for 1,25-dihydroxyvitamin D decline in quantity with age
Older animals are also less able to mobilise calcium from bone
Older animals have a greater milk production = greater demand for calcium
Breeds such as Channel Island, Swedish Red and White, and Jerseys are all more susceptible to milk fever than Holsteins
One study showed that intestinal receptors for 1,25-dihydroxyvitamin D are around 15% less in Jerseys than Holsteins
Metabolic alkalosis (MA)
Mostly caused by a diet that supplies more cations (K, Na, Ca and Mg) than anions (Cl, SO₄ and PO₄) causing a difference in
electrical charge in body fluids
MA has been shown to blunt the homeostatic response of dairy cows to parathyroid hormone because it is believed that it
causes a change in conformation of the parathyroid hormone receptor in all target tissues
Thus the cow cannot benefit from these homeostatic mechanisms and restore plasma calcium
Low levels of magnesium also interferes with the ability of parathyroid hormone to act on its target tissues
Particularly in relation to magnesium’s action as a co-factor allowing parathyroid hormone to stimulate cyclic AMP production
(necessary for operation of calcium channels)
Prevention of hypocalcaemia
Prevention of hypocalcaemia, not just milk fever, should be a major goal of dairy farms
The DCAD method
Induce a compensated metabolic acidosis in the cow restoring the ability of parathyroid
hormone to regulate blood calcium levels.
Reduce dietary cations and to increase dietary anions.
Causing a reduction in what is known as the Dietary Cation-Anion Difference (DCAD),
subsequently lowering the pH of the blood.
(Source: Horst et al. 2005)
Prevention of hypocalcaemia continued …
Feeding a calcium-deficient diet
Reducing calcium in diet prior to calving
Diets less than the required concentration of calcium can cause a slight decline in plasma calcium
stimulating increased release of parathyroid hormone
Implemented days prior to parturition the homeostatic response, including osteoclastic bone resorption,
is already active and the cow is able to utilise calcium with maximum efficiency
Demand for calcium is more easily overcome and hypocalcaemia can be avoided
Higher dietary Magnesium
A higher dietary magnesium concentration prior to calving ensures that passive diffusion of magnesium
in the rumen can occur and levels of magnesium in the blood will be adequate
Should be implemented as early as possible
Restores plasma calcium level
Fastest: IV injection of calcium salts, usually calcium borogluconate
(recommended 2g Ca/100 kg bodyweight)
Administer the Ca at a rate of 1 g/ min
While listening to the heart to avoid fatal arrhythmia
Oral gels containing calcium salts are given before, during and around 12-24
hours after parturition as a preventative treatment measure
Economically important
Affects productivity
Reduces a dairy cow's productive life.
It costs the dairy industry not only through loss
of production but also in the cost of control and
treatment measures.
• Prevention is key
• Future research focus on regulatory mechanisms
of calcium metabolism.
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