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

HYPOCALCAEMIA

in dairy cattle

Sophie Rosevear, Jessie Neal, Tara Hall and Alex Doddridge

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 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

• • • •

Age

Most common in cows in 3 rd 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 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

• • • • • •

Treatment

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

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.

REFERENCES

Bigras-Poulin, M. & Tremblay, A. 1998, ‘An epidemiological study of calcium metabolism in non-paretic postparturient Holstein cows’, Preventive Veterinary Medicine vol. 35, pp. 195-207 DeGaris, P. J. and Lean, I. J. 2007, 'Milk Fever in dairy cows: A review of pathophysiology and control principles', The Veterinary Journal vol. 176, no. 1, pp. 58-69 El-Samad, H., Goff, J.P. and Khammash, M. 2002, ‘Calcium homeostasis and parturient hypocalcaemia: An integral feedback perspective’, Journal of Theoretical Biology vol. 214, pp. 17-29 Goff, J.P. 2008, ‘The monitoring, prevention, and treatment of milk fever and subclinical hypocalcaemia in dairy cows’, The Veterinary Journal vol. 176, pp. 50-57 Goff, J.P., Reinhardt, T.A. and Horst, R.L. 1991, ‘Enzymes and factors controlling vitamin D metabolism and action in normal and milk fever cows’, Journal of Dairy Science vol. 74, no. 11, pp. 4022-4032 Goff, J.P., Ruiz, R. and Horst, R.L. 2004, ‘Relative acidifying activity of anionic salts commonly used to prevent milk fever’, Journal of Dairy Science vol. 87, pp. 1245-1255 Hamali, H. 2008, 'Post estrus hypocalcemia in a repeat breeder half-breed holstein cow', Journal of Animal and Veterinary Advances vol. 10, pp. 1301-1304 Hangping, C., ZhongHua, W. and Fuchang, Li 2010, 'Effects of dietary calcium levels on calcium homoeostasis in lactating dairy cows', Chinese Journal of Animal Nutrition vol. 22, no. 5, pp 1286-1292 Horst, R.L. 1986, ‘Regulation of calcium and phosphorus homeostasis in the dairy cow’, Journal of Dairy Science vol. 69, pp. 604-616 Horst, R.L., Goff, J.P. and Reinhardt, T.A. 1994, ‘Calcium and vitamin D metabolism in the dairy cow’, Journal of Dairy Science vol. 77, pp. 1936-1951 Horst, R.L., Goff, J.P. and Reinhardt, T.A. 2005, ‘Adapting to the transition between gestation and lactation: Differences between rat, human and dairy cow’, Journal of Mammary Gland Biology and Neoplasia vol. 10, no. 2, pp. 141-156

REFERENCES continued

Kimura, K., Reinhardt, T.A. and Goff, J.P. 2006, ‘Parturition and hypocalcaemia blunts calcium signals in immune cells of dairy cattle’, Journal of Dairy Science vol. 89, pp. 2588-2595 Kronqvist, C., Emanuelson, U., Sporndly, R. and Holtenius, K. 2011, 'Effects of prepartum dietry calcium level on calcium and magnesium metabolism periparturient in dairy cows', Journal of Dairy Science vol. 94, no. 3, pp. 1365-1373 Lean, I. J., DeGaris, P. J., McNeil, D. M. and Block, E. 2006, 'Hypocalcemia in dairy cows: meta-analysis and dietary cation anion difference theory revised', Journal of Dairy Science vol. 89, pp. 669-684 McNeill, D. M., Roche, J. R., McLachlan, B. P. and Stockdale, C. R. 2002,'Nutritional strategies for the prevention of hypocalcaemia at calving for dairy cows in pasture-based systems, Australian Journal of Agricultural Research, vol. 53, no. 7, pp. 755-770 Oba, M., Oakley, A.E. and Tremblay, G.F. 2011, ‘Dietary Ca concentration to minimise the risk of hypocalcaemia in dairy cows is affected by the dietary cation-anion difference’, Animal Feed Science and Technology vol. 164, pp. 147-153 Peacock, M. 2010, ‘Calcium Metabolism in Health and Disease’, Clinical Journal of the American Society of Nephrology vol.5, pp. s23-s30 Radositis, O.M., Gay, C.C., Hinchcliff, K.W. and Constable, P.D. (2007), 'Veterinary Medicine - A textbook of the diseases of cattle, horses, sheep, pigs and goats,' Saunders Elsevier, worldwide (Sydney) Reinhardt, T. A., Lippolis, J. D., McCluskey, B. J., Goff, J. P. and Horst, R. L. 2011, 'Prevalence of subclinical hypocalcemia in dairy herds', The Veterinary Journal vol. 188, pp. 122-124 Ramberg, C.F., Johnson, E.K., Fargo, R.D. and Kronfeld, D.S. 1984, ‘Calcium homeostasis in cows, with special reference to parturient hypocalcaemia’, America Journal of Physiology vol. 246, no. 15, pp. R698-R704 Schenck, P. A. and Chew, D. J. 2008, 'Hypocalcemia: A Quick Reference', Veterinary Clinic Small Animal vol. 38, pp. 455-458 Shahzad, M. A. and Mahr-un-Nisa, M. S. 2008, 'Influence of varying dietary cation anion difference on serum minerals, mineral balance and hypocalcemia in Nili Ravi buffaloes', Livestock Science vol. 113, pp. 52-61

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