Did you know your cows are made of a lot of metal?

Over a dozen metals are used by the body, for example Iron is a crucial component of blood allowing oxygen to be carried around the body.

A lot of the other metals involved in metabolism we will have heard of like Copper, Zinc and Selenium. Perhaps you won’t have heard of some of the ones needed in tiny quantities like Nickel, Boron and Chromium. Most unlikely of all are some elements we know are highly toxic but in fact cause poor growth if completely absent in the diet like Arsenic (oh yes it is a metal, go on Google it!).

The one we are going to focus on is ten times more abundant than all the other metals in a dairy cow’s body, in fact a 700kg Holstein would contain 10kg of the stuff. This metal is calcium and she needs every gram. Over 98% of it is in her bones, providing strength to the skeleton but the last 1 or 2% (10-15g) is critical to her life as it allows muscles to contract properly.

How important is it and what can go wrong?

Very important! A cow needs just 3-4g of calcium in her blood and around 9g in her muscle tissue fluids to maintain muscle strength. She keeps around the same amount again in a dissolved form in her bones, that can be drawn on quickly, but the rest of the 10kg she has is locked up in the bone structure itself. Like all good mothers, the dairy cow provides for her children first and colostrum contains about 2g per litre (twice as much calcium as milk). So when a cow bags up to calve, she drains her crucial blood calcium levels several times over, depending on how much colostrum she makes. That is when we see ‘Milk Fever’ or in technical terms ‘clinical hypocalcaemia’. There are 3 stages of symptoms we see as calcium levels drop.

Stage one milk fever we rarely see as vets. The signs are subtle and often go unnoticed as they vary between animals in severity. Some appear more excitable than usual, while others are weak and wobbly. It is a case of the cow being not quite herself and given she is near or recently calved a good stockperson will know this is early milk fever.

Cows in stage two milk fever cannot stand but will be lying in an upright posture. They will be obviously weak and depressed, often have an ‘s-shape’ to the neck and a dry nose. If untreated they will inevitably deteriorate to stage three, though the time this takes varies massively depending on how severe the calcium deficiency is.

Having reached stage three the cow has less than a couple of hours to live. She will be on her side, severely depressed and paralysis will be setting in. She is also likely to bloat in this position and this will kill her, if no bloat occurs, the paralysis will progress to coma and death anyway.

How do we treat it?

Ideally prevent it (...more on that later). When presented with a cow with milk fever she urgently needs calcium to arrest the progression to death. She will need a calcium solution injection and you probably already have a way of treating these cow, however, there are a few myths that need dispelling about the best way to do this.

A hypocalcaemic cow will only need 6-12 grams of calcium in her blood to recover, a 40% bottle of calcium contains 12g and a 20% bottle of calcium contains 6g. It should be given in the vein if the cow is in stage 2 or 3 but too much calcium given too quickly will cause a heart attack in the cow. So it is crucial that you are aware of how much calcium is in the bottles that you have on farm and to administer it slowly (1g per minute as a rule of thumb) under careful observation, stop immediately if you have any concerns.  If in doubt, ask your regular vet what is appropriate for your cows and have farm staff trained by us in how to give it safely. If the cow is on her side and bloated, it is usually advisable to sit her up to allow some gas to escape, but don’t waste time as she needs the calcium urgently too.

Successful treatment will result in her muscles starting to tremble and she may begin cuddling. Not all cows will get up straight away but seek further vet advice if she is not standing within an hour.

At the same time, calcium can be administered under the skin (subcut), this is often all that is needed for stage 1 milk fever. However, if a bottle of 40% calcium has been given in the vein, further injections of calcium are not necessary at the same time. In fact I/V calcium will last 4 hours in her system and subcut only 6 hours, the more calcium she has the faster she will excrete it in her urine. This surplus may trigger her body not to reduce absorbtion of calcium from the diet and to reduce mobilisation of her own bone calcium reserves. So it is far better to administer an oral calcium supplement at this stage, this will give her a much longer reserve and maintain her ability to absorb calcium from the diet which is better in the long term. Not all oral supplements are the same, so ensure product specific instructions are followed and discuss with one of us if in doubt.

I know how to treat it, how do I prevent it more effectively?

Before we get to prevention, there is one other condition to be aware of, subclinical hypocalcaemia. Subclinical means we don’t see obvious clinical signs (i.e. no weakness/recumbency) but the condition is still there, the calcium levels are lower than normal but not so low we see the obvious signs. Most herds with sub-optimal milk fever management will have around 50% of the cows going into subclinical milk fever, but may only see 5-10% of cows showing milk fever. We also know most cows don’t get milk fever until the 2nd lactation, but heifers can get subclinical milk fever and this is often not appreciated. Also bear in mind if you give calcium routinely/preventatively at calving you will prevent serious cases but not the subclinical effects. Subclinical milk fever and clinical milk fever makes cows prone to a number of other problems (see table 1), the knock on effects are therefore estimated to be about £80 per cow with subclinical milk fever, which could be £4000 per 100 cows per year on your farm. Far more costly than careful prevention.

It is easy to see how these other problems occur as a knock effect to sub-clinical milk fever, for example if the muscles don’t work well in her gut, she will be prone to a bigger energy deficit, fat mobilisation and all the knock effects to fertility and increased LDA risk. If the uterus does not contract and expel the cleansing quickly, she will be prone to problems there too. But there is another affect occurring, low calcium decreases the activity of some immune cells. This also makes mastitis and metritis much more likely.

So prevention is crucial, and in theory easy! We have essentially 2 choices:

1. Reduce calcium availability to the cow to a bare minimum, 3 weeks prior to calving. This will encourage the cow to be more efficient at extracting calcium, so when she gets the milking ration immediately after calving, she absorbs all the calcium she needs. It also mobilises more calcium absorption from the bones, so she has a larger reserve pool there at calving.  To achieve that calcium, intakes must be less than 50g/day, ideally around 20g/day which is almost impossible to achieve with grass based forages. Instead, we can bind up the calcium in the ration and prevent absorption with products such as zeolite. It is not without complications, so discuss with your vet and nutritionist for best results.
    
2. Using a DCAB diet, if we cut through what DCAB stands for and the detailed science this is essentially a way of feeding the cow to slightly acidify her blood. Do not confuse this with rumen acidosis! The slightly acidic status of her blood results in a natural increase in vitamin D3 which stimulates more effective calcium absorption from the diet and cow’s own bones. As such, calcium must be supplemented not restricted on DCAB diets. It can be highly effective but cannot be relied upon through guess work, a bespoke mineral pack is required in the ration and analysis of forages crucial.

   Monitoring of the cows’ urine pH is the only way of ensuring the DCAB is correct. Discuss with us how to do this if you are not doing so.

Milk Fever increases the chance of these conditions:

Table 1

I don't think I have a problem with milk fever, how can I be sure?

If you don't have total control of your dry cows' diet you will have a problem with calcium metabolism, or you are very lucky!  Remember you may only treat a handful of cases of milk fever but 5 or 10 times that number of your cows will have had subclinical milk fever. Because of this, the biggest economic cost actually comes from the subclinical cows (the ones you won't actually see signs of milk fever in).  Remember these cows are at greater risk of just about every common problem affecting dairy cows.
 
So, for example, if you have more cows with metritis and whites than you would like it may well be worth checking for subclinical milk fever. There is only one way to establish a cow's calcium status around calving and know definitively you do not have a problem with subclinical milk fever in the herd.
 
A relatively inexpensive blood sample analysis will reveal the problem, but timing is crucial. We need to take this sample within 24 hours of calving, 1st milking is usually a convenient time. Don't worry it need not involve calling out the vets for every freshly calved cow!  We can train members of farm staff how to do it and the do's and don'ts. The samples will be stable, kept in a fridge for a few days and you can drop them in to the surgery or have us collect them at a routine fertility visit. Results will be available for us to interpret in 24 hours, or if necessary, on the same day at slightly higher cost. A more proactive monitoring and management strategy will save a lot of time, effort and money in the long term so have a chat with one of us if you want to know more.

To discuss this further, please call the practice and speak to a member of the farm team 01363 772860, alternatively, please click the link to view our factsheet - Milk Fever.