NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare.

Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.

Milk fever

The NADIS data show that October is the peak month for milk fever. This is almost certainly because controlling intakes in dry cows outside is at its hardest in late summer early autumn.

However milk fever is also a common disease all year round. Like most metabolic diseases it is important to remember that for every cow that shows clinical signs, there will be several more which are affected sub-clinically.

What is milk fever?

Milk fever (or hypocalcaemia) occurs when the cow mobilises its body reserves of calcium (primarily into milk) too quickly. This results in a rapid drop in blood calcium, which becomes too low to support normal nerve and muscle function. The cow then collapses and becomes unable to stand until its blood calcium becomes normal again. Muscles other than limb muscles are also affected. Gut movement stops leading to constipation, womb contraction stops leading to prolapse and/or retention of the afterbirth, and the teat sphincter opens leading to increased mastitis.

Clinical signs

· Loss of appetite and lethargy

· Constipation

· Swaying and muscle tremors

· Collapse – sitting on breast bone. Initially with a ‘swan neck’

· Severe depression

· Collapsed onto side

· Death

Where milk fever develops during calving, calving slows down dramatically and, in most cases, stops all together. Hypocalcaemia is one of the most important causes of calving problems and subsequent calf deaths.

Diagnosis

Clinical signs are very suggestive. However, many other diseases can be superficially similar to milk fever. In particular it is essential to rule out toxic mastitis and physical injury, such as broken bones or nerve damage before treating a case.

Blood test: Taking a blood sample before treatment is very useful. In most cases it will not be used, but, in cases that do not respond to treatment, it can be very useful in confirming that milk fever was the primary problem or in identifying other significant problems, such as low blood magnesium.

In many cases response to treatment is the best diagnostic method, with cows becoming brighter and more alert within minutes of intravenous treatment.

Treatment

Most cases of milk fever will respond to treatment with a single bottle of calcium. This is much more effective if it is given into the vein, as when given under the skin, blood calcium levels can take up to four hours to return to normal.

Some cows with milk fever have low blood magnesium and phosphorus. In most cases these will return to normal even if only pure calcium is given. Combined calcium, phosphorus and magnesium products have no significant advantages over straight calcium. If a cow has very low magnesium and low calcium then considerably more magnesium is required than is present in a combined product.

Relapses do occur (in around 20%) of cases. In this case the same treatment is repeated, although it is worth checking a blood sample to ensure there are no other metabolic problems. Following intravenous therapy with ‘another bottle under the skin’ does not seem to prevent relapses.

Prevention

Prevention of milk fever is a huge subject, which cannot be properly covered in an article such as this one. If you have a milk fever problem you need to discuss a strategy with your vet and nutritional adviser.

However, the common strategies can be divided into three, which are summarised below:

1) Low calcium strategy (often with relatively high phosphorus):

This is the strategy that’s most commonly used in the UK and is still effective on many farms. It works by ensuring that the dry cow is mobilising calcium, so that when it switches to milk production it is better able to cope. A useful analogy is to think of the lactating cow as an athlete, it’s much more likely to do better if it has a bit of training before it needs to compete. Low calcium in the dry period provides that training.

2) DCAD strategy

This strategy was developed in the US in order to combat the high potassium in their forages, which prevents the low calcium strategy from being effective. Altering the balance of the diet by feeding an excess of strong anions (primarily chloride and sulphide) would change the pH of the blood, if the body’s mechanisms didn’t prevent it. One of the mechanisms that prevents this is the calcium metabolism, thus feeding an ‘anionic diet’ is another way of training the cow before it starts milking. This can be very effective, but it is more difficult to undertake than the low calcium strategy (with which it mustn’t be combined). Potential problems include low palatability of some anionic salts and the requirement for regular urine pH testing. If the DCAD strategy is not done correctly it can lead to significantly increased milk fever levels.

3) Drenching or pasting

Several commercial products are available for boosting blood calcium. Best results are obtained if the first dose is given before calving (usually around 8 hours before) with a second dose 24 hours later. This obviously requires calving to be accurately predicted. This method is used more commonly in Europe than in the UK, and is more time consuming and has less economic benefit than good dry cow nutrition. It is probably bets used in herds suffering from a high level of metabolic disease around calving.

Whichever technique is used, good dry cow management is essential. The transition between dry and milking needs to be as seamless as possible. Also, whichever prevention route you choose make sure that all cows receive plenty of magnesium, as low magnesium intake is one of the most important causes of milk fever.

Richard Laven PhD BVetMed MRCVS