Milk fever: the problem of low blood calcium in cattle

Milk fever is a common condition, predominantly of periparturient (around calving time) dairy cows of all breeds, and refers to a state of low blood calcium. It can also affect suckler cows and ewes.

Cause

While the cow/ewe has a massive store of calcium in her bones, there is only a small amount circulating in the blood. If blood calcium levels are extremely low, clinical milk fever will be seen. However this should be seen as a warning sign for a larger problem as it is likely that there are many more animals on the farm with subclinical hypocalcaemia, ie sub-normal blood calcium, which will have knock-on effects on feed intake, periparturient disease and fertility.

Usually with clinical milk fever 75% of cases will occur within 24 hours of giving birth, with most other cases occurring between 24 and 48 hours after giving birth. Hypocalcaemia at or before calving/lambing is associated with delayed calving. Older cows and ewes tend to be more susceptible to milk fever as they have decreased ability to mobilise calcium from their bones. Fat animals are also more susceptible to milk fever.

Hypocalcaemia occurs around calving in dairy cows due to increased demand for calcium at this time in association with the onset of lactation, with a resultant sudden and severe outflow of calcium from the blood into the milk. Low dietary calcium in the dry cow diet is very important in stimulating parathyroid hormonal axis to mobilise calcium off the bone.

In some cases of milk fever there will be simultaneous hypophosphataemia (low blood phosphorus) due to loss in milk or decreased absorption (decreased intake in feed or decreased mobilisation from bone). A further predisposing factor to parturient hypocalcaemia is low blood magnesium. High potassium in the diet reduces the availability of magnesium in the diet. High potassium is a feature of silage which has received high levels of slurry application.

Symptoms

Calcium is needed for muscle contraction in the body and, therefore, clinical signs are mainly related to muscle weakness and paralysis. In general, there are three main stages to clinical milk fever. Affected animals in stage one have symptoms consisting of mild excitement (muscle twitching) without recumbency. These animals also have little or no appetite and progress on to stage two after an hour or so. In stage two (lasting one to 12 hours), there is depression, paralysis and recumbency. The head is characteristically turned into the flank or rested on the ground in an extended position. Fine muscle tremors may be evident and the cow/ewe may make threatening motions with the head, eg head-shaking or open-mouth bellowing.

The head in extension may have an s-shaped appearance, ie the ‘swan-neck’ presentation. The vet will find less audible heart sounds on examination at this time, usually with decreased temperature. Uterine prolapse is not an uncommon sequel to this stage. Animals with stage three milk fever exhibit further weakness and progressive loss of consciousness. Bloat may occur if they fall into a lateral recumbency and this may be life-threatening. There is a danger of aspiration pneumonia (animal brings up fluid from the rumen due to relaxation of the oesophageal sphincter and breathes it into her airways) and, if untreated, death usually occurs in three to four hours.

Subclinical hypocalcaemia can manifest in many ways, including increased incidence of retained placenta, metritis, displaced abomasum, toxic mastitis and excessive weight loss after giving birth due to poor feed intake.

Treatment

The disease should be treated as an emergency, especially if the animal is at stage three. Cows should receive 400ml of 40% calcium borogluconate intravenously and a further 400ml subcutaneously (under the skin) using a flutter valve and a 14 gauge needle. Your vet will listen to the heart periodically during administration of the intravenous calcium and may decide to give a second bottle intravenously, depending on cow size and findings on clinical examination.

An 80ml dose of the 40% solution is adequate for a large ewe if administered under the skin. This should be administered as a divided dose in three or four different sites, with the side of the ribs being an ideal location as the skin is loose here.

Within 30 minutes of treatment, 60% of animals with uncomplicated milk fever will stand. Some cows that fail to stand following therapy may respond to treatment with injectable or oral phosphorus. Full restoration of calcium homeostasis takes two to three days, and therefore, further treatment will be necessary in a percentage of cases. If the animal remains recumbent, she should be propped in sternal recumbency in an area with good underfoot conditions and easy access to food and water. The animal should be rolled from side to side four to five times a day and assisted to rise if possible.

For dairy cows, it is advisable to consider only partial milking for one or two milkings post treatment once the cow is standing again to reduce the risk of a relapse.

Prevention and control

There are a number of important preventative measures that should be considered. One of the most important factors is the dry cow and ewe diet. It is vital that there is a high level of magnesium in the diet to stimulate parathyroid hormone activation and to optimise the ability to mobilise calcium from an animal’s bones. Apart from ensuring that minerals being fed are high in magnesium, it is also important that they contain very little or no calcium.

Body condition scoring of cows at drying off is important, followed by appropriate feeding so they can calve down fit, not fat (BCS of 3.0). A potential option that can be very successful on some farms, especially where high potassium silage is contributing to the problem, is to alter the diet. This is not an option to undertake without consultation with, and monitoring by a nutritionist/veterinary practitioner.

Vitamin D3 preparations administered before calving/lambing may prevent or reduce the clinical signs of milk fever but the timing of injection is critical; ie they must be given two to seven days before calving/lambing. This requires accurate calving dates to ensure the cows the Vitamin D3 is administered.

Other preventatives include culling cattle and ewes prone to the condition, especially older animals, and administering oral calcium at calving/lambing.