HYPOCALCAEMIAin dairy cattle

Sophie Rosevear, Jessie Neal, Tara Hall and Alex Doddridge

(Source: http://www.eyefetch.com/image.aspx?ID=405372)

Introduction• Calcium is essential, it is involved in many physiological processes.

• Dairy cows have been heavily selected for the ability to produce high milk

yields.

• There is a fine calcium balance in the dairy cow.

• When demand for energy and calcium suddenly increases this balance is

disrupted.

• Calcium homeostasis fails = milk fever (also called periparturient paresis)

• Affects productivity and longevity of high producing dairy cows

Calcium

(Source: Horst 1986)

Calcium homeostasis

Failure of homeostasis and development of hypocalcaemia

• Lactation generates a sudden, very high demand on calcium homeostasis

• Causing 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

• 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

(Source: http://informedfarmers.com/dairy-cattle-industry/downer-cow/)

Predisposing factorsAge• 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

Breed• 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

Hypomagnesaemia• 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 hypocalcaemiaPrevention 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 to increase calcium efficency

• 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

Treatment

• Should be implemented as early as possible

• Restore the plasma calcium

• 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

CONCLUSION

• 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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