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Do we really know about milk fever?

Do we really know about milk fever?Over the next four months we will be looking at milk fever in more detail and examining the impact it can have on animal health and productivity. Here, in the first of the four articles, Richard Cooper, a veterinary surgeon from the Evidence Based Veterinary Consultancy, examines some of the popular misconceptions about this very costly, yet preventable disease.

There are very few farms which can claim they have never seen a case of milk fever (hypocalcaemia). While clinical cases of milk fever are the ones we tend to remember, from a cost and health perspective these only represent ‘the tip of the iceberg’. Subclinical milk fever is an extremely common finding on farms and the losses it brings in terms of production, reduced fertility and other metabolic disease should not be underestimated. Many farmers just accept the odd case of clinical milk fever, but need this be the case?

Misconception
■ Administering calcium to animals without milk fever around the time of calving can increase the risk of milk fever problems.

Truth
■ Injectable calcium could have this effect by dampening down the cow’s natural mechanisms to mobilise calcium reserves (bones and guts). However, oral calcium does not cause these problems with the right balance of calcium salts. Injectable calcium is vital when a cow is showing clinical signs of milk fever to provide lifesaving calcium directly to where it is needed. In addition to the beneficial effect of providing supplementary calcium, administering oral calcium boluses containing calcium chloride and calcium sulphate potentially increases access to calcium reserves in bone by making the body more acidic. Administering a calcium bolus is therefore good practice, particularly in at-risk animals around the time of calving.

Misconception
■ The occasional case of clinical milk fever is normal, just as are the occasional cases of mastitis.

Truth
■ Milk fever is largely preventable, so there is no need to put up with the ‘occasional’ clinical case. Diet management, particularly during the transition period, and minimising other stressors around calving are important. Use of supplemental oral calcium in at-risk animals can also help in reducing risk at an individual cow level.

Misconception
■ Milk fever is just a transitory problem around calving and once the cow has recovered there are no lasting effects.

Truth
■ Yes, the results of administering intravenous calcium to a clinical case are essential for recovery from a clinical case. However, there are long-lasting detrimental effects of animals experiencing clinical or subclinical low blood calcium. Consequences includei,ii:

■ Lowered immunity.
■ Slower rumen, abomasal andgut turnover.
■ Reduced uterus contraction strength during and after calving. The result of these is an increase in risk of early lactation conditions such as metritis, dystocia, retained placenta, LDA, ketosis and mastitisiii, and reduction in yield and fertility in that lactation.

Misconception
■ Milk fever is only an issue when you see a downer or wobbly cow.

Truth
■ Clinical cases are the ones where you can see the symptoms of low blood calcium, such as ‘down cows’ or unsteadiness on her feet. However, for every clinical case there are likely to be 3 to 6 sub-clinical cases in the herd. Most dairy cows suffer some degree of hypocalcaemia at calvingiv with lowest levels being seen the day of calving or the day after. Sub-clinical means you will not see any symptoms, but the animal’s health and productivity will be suffering as a result of low blood calcium and may not develop into clinical milk fever. It normally takes around 4 days for calcium levels to recover. Herds can suffer from the sub-clinical form with no clinical cases at all.

Misconception
■ It is better to wait to see a case of milk fever before taking action.

Truth
■ By the time you see one clinical case there will be other animals in the herd suffering sub-clinically. Managing milk fever should form part of your farm feeding and health plan – it is a cheap disease to prevent but a costly disease to live with. Dietary management of all dry cows, and use of oral calcium boluses to reduce the risk of milk fever are effective and practical ways to address it. Routine monitoring of fresh cow blood calcium, or urine macromineral testing of transition cows, can spot potential problems early.

Misconception
■ Cows are designed to eat grass, and this makes for a good diet for dry cows.

Truth
■ Modern farming practices designed to promote ley productivity have resulted in grass silage and grazing that is high risk for milk fever – in particular the use of potassium-rich fertiliser (potash and slurry/manure).

If using grazing or grass silage, try to assign fields for dry cow forage production and grazing, and minimise ‘K’ application. Later cuts tend to be safer and, if at grass, keeping grazing close particularly during spring and autumn flushes to reduce risk. Alternative forages, such as maize, wholecrop and straw, are naturally lower in potassium (the root of most milk fever problems), and can be used to ‘dilute’ potassium intake from grass silage.

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