Milk Fever

A property owner in the Darwin region reported two downer cows out of a herd of 12 Bos taurus cattle. The cows had been on the property for a few years, and there had been no recent management changes. The cows had had access to a bull. There was no supplement lick and there had been a number of recent storms. A cow was seen to be acting unusually, before being found down and then dead the next day. When a second cow was found down the regional Veterinary Officer and Livestock Biosecurity Officer were called to investigate.

On examination the cow was unable to move the legs or tail, and there was no deep pain response. There were no obvious signs of calving or trauma and the cow had a fever (40.2C). There were normal cow pats near the cow and no signs of struggling. The cow was euthanased for post mortem examination.  Post mortem showed the cow to be in late pregnancy. There was significant bruising in the muscles and other tissue, the urine was dark and the kidneys enlarged. The calf was a bull calf, and the liver broke up more easily than expected. A range of samples were taken for lab testing, which showed low calcium (hypocalcaemia), muscle damage and breakdown of the liver.

Based on the findings of the post mortem and the samples collected, a diagnosis of milk fever was made. Milk fever is uncommon in the NT, and is generally associated with dairy cattle that produce a large quantity of milk; however, it can also occur in beef cattle. Milk fever is caused by low calcium in the blood; this causes a decrease in muscle function which can result in weakness, recumbency, depression and ultimately death. Pasture usually contains enough calcium to meet the minimal requirements of cattle, however a dramatic increase in calcium requirements occurs with the onset of lactation in the cow.

For this small managed herd the following recommendations were given and no further losses were reported:

• After joining, keep cows on a low calcium diet (ie. high in roughage and low in green feed) and make sure they don’t become over fat.
• In the few weeks prior to calving,keep cows in a close paddock and observe them frequently. If down cows are noted and milk fever is suspected, consider administering a 3 in 1 or 4 in 1 vaccine treatment and contact a vet.
• Consider shortening the joining period so that approximate calving dates are known. This will make it easier to manage feeding and observation close to calving.