Low calcium is often the beginning of a much bigger problem...

By Katrina Roberts, Anexa FVC Herd Health Veterinarian

Over the last couple of years, we have undertaken some exciting research into issues with transition cows, and we are pleased to share some of our findings with you.

1. Low calcium is often the beginning of a much bigger issue, and we (or at least some of us) DO have a problem.

Our research showed that the average clinical prevalence of farmer-reported milk fever across 77 herds was 4.6% of the cows in a season. When you compare this to a realistic target of 1 to 2%, you can see why we have an issue. In addition, the average prevalence of subclinical hypocalcaemia (low calcium) measured in the blood of over 1000 cows, within 2 days of calving, was 33%.

On the day of calving, there is a huge change in a cow’s calcium requirement, and we can expect some cows to get it wrong. And, if this happens, they sit down within 48 hours of calving. However, we should not be getting down cows any other time; if you are, you need help!

Do you know whether you have a problem? The only way you can know is if you measure (take some bloods on the day of calving) and, record ALL your down cows.

2. But so what – a few down cows – they get up don’t they?

We know that an average cow is only low in calcium for about 24 hours after calving however, we also know older cows stay low for longer (6+ year olds), therefore increasing the risk of sitting down in the colostrum mob.

Young cows (second calvers) can have low calcium levels too. In our study, 10 to 15% of the 3 year olds had subclinical hypocalcaemia. The 3 year olds that were low in calcium had a 30% lower 3-week incalf rate compared to the 3 year olds that had normal calcium levels; this was driven by lower first service conception rates.

We know that low calcium reduces the performance of the cow’s immune system. We also know that cows with clinical milk fever have poorer outcomes with regard to overall health, production, reproduction and survival. Overseas data repeatedly shows these cows have more other health issues and are less likely to get back in calf. At this point we don’t have good New Zealand data on this because clinical milk fever is poorly recorded on farm. However, when we have analysed the reproductive performance of recorded milk fever cows in our incalf herds, we consistently see lower 6-week incalf rates in the milk fever cows compared to their same age herd mates. And, overseas research also indicates that cows with subclinical hypocalcaemia are more likely to have uterine infections.

So how much is your current milk fever problem affecting your herd? Are there any clues that low calcium could be contributing to your below target performance?

3. So what can I do - do I have to buy all that fancy stuff?

In most herds, the basics work (refer to last year’s transition article here: www.anexafvc.co.nz/factsheets - Managing the cow over the calving period), but this is not always the case!

Springing cows need about 40 g of elemental Magnesium. They will get about 20 g from their diet and therefore need to be supplemented with a further 20 g. In our survey of 77 local herds, cows were getting on average two times that amount down the throat, and yet we saw 33% of cows with subclinical hypocalcaemia!

It is recommended to use more than one form of Magnesium for the springers if you can (such as Magnesium sulphate, Magnesium oxide or Magnesium chloride). Collect new calves from the springer mob twice a day, and take the freshly calved cows to their fresh feed with their Magnesium and calcium allocation as soon as possible after calving.

For those high risk cow (6+ year olds, cows with BCS of >5, Jerseys and cows that sit down every year), give a calcium supplement immediately after calving, however this will need to be repeated at least every 12 hours. IV calcium is not recommended as a preventative as it causes a rapid spike in blood calcium, which is followed by a rapid drop. If you do use IV calcium, it should be given with an oral calcium drench or a bag under the skin.

If you have a number of mature cows that have a BCS of >5, then this group may need to be managed separately pre-calving and offered 90% of maintenance requirements instead of 100%. Mineral supplementation of late calving cows is often haphazard as they become a smaller mob and more difficult to dust with Causmag. You may consider using an alternative strategy to supplement their diet with Magnesium such as a mag bullet.

Colostrum cows are the most important and most annoying mob on the farm. Feed them ad libitum high quality feed and do not skimp on calcium. How you choose to give them calcium is farm dependent (oral drenches, dusting their break or mixed in with the feed) but you need to be aware of the potential limitations of your method. For example, a one off starter drench isn’t going to ‘fix a wobbly cow’, it may stop her sitting down but it won’t necessarily prevent the subclinical effects of low calcium. Colostrum cows are more interested in looking for their calf than eating, so if the PK trailer with lime flour mixed in it is at the back of the paddock you can understand why the colostrum cows aren’t eating it. Milking the colostrum cows once-a-day may be a possibility, however this management change will need some discussion with your Vet to factor in mastitis management and withholding periods of dry cow antibiotics.

So there are some extra things you can do to minimise the number of cows with low calcium at calving, you just need to work out what is practical for your farm.

4. Can I tell if all this extra effort is working?

Yes, recording clinical cases will enable to track your progress, but an earlier measure than that is by blood testing. A sample (10) of freshly-calved cows can be blood tested for calcium, and energy status.

If you would like further information, please talk to your lead Anexa Vet or contact one of our Herd Health Advisors.

Date Added: Thursday, 8th June 2017