Farm Ireland

Monday 25 March 2019

Subclinical milk fever is the main factor behind rise in slow calving

Restricting calcium intake and supplementing magnesium in a cow's diet six weeks prior to calving can help prevent this ­condition, writes vet Eamon O'Connell

According to the veterinary text book, a cow should calve two to five hours from the moment the water bag is seen
According to the veterinary text book, a cow should calve two to five hours from the moment the water bag is seen

"She should have calved four hours ago but there's still no sign of a calf. It's like she's forgotten what to do! I think you might have to have a look at her!"

This was the voice of a very anxious client at 11pm one night last week. As I drove to the farm, I began to realise that this is becoming a common theme already this spring. We are seeing a lot of cows that are slow to progress through the stages of calving and often, by the time we get called to them, it can be too late for the calf.

According to the text book, a cow should calve two to five hours from the moment the water bag is seen.

The cow will usually spend a lot of this time lying down and "forcing" with each contraction. If a cow is in the full throes of labour for more than two hours after the water bag is visible, and there is still no sign of the calf's feet protruding from the vagina, then she should be handled as the calf may be too big or have an abnormal presentation.

What we are seeing more so this spring, however, is what many people refer to as a "slow calving".

The cow begins to show signs of labour but, after a number of hours, she will have not progressed any further. The cow may only have intermittent slight contractions and seem unaware that she should have calved at this stage. The most common cause of this is subclinical milk fever.

We all know what clinical milk fever looks like - a cow presents down after calving and cannot stand. Milk fever is only the tip of the iceberg, however. For every one case of clinical milk fever, there can be up to 10 cases of subclinical milk fever. Slow calving and subsequent retained placenta is characteristic of subclinical milk fever. Not only does this put the calf at risk, but it also puts the cow at risk. Uterine infections, mastitis, displaced abomasums and infertility are all knock-on effects of this condition. Studies have shown that the annual cost of subclinical milk fever can be greater than €6,000 in a 100-cow herd. So, what can we do to prevent it?

Manipulation of the dry cow diet is the basis for any prevention plan when it comes to milk fever. In order to implement a successful control plan, it is vital that a full grass silage analysis is performed including, most importantly, a mineral profile.

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The simplest method is by restricting calcium and supplementing magnesium in the six weeks prior to calving. Cows need 42g/cow/day of magnesium in the diet to prevent milk fever. Most of the higher spec pre-calving minerals have a minimum of 22pc magnesium. When fed at 100g/head/day, this means that another 20g needs to be provided by the grass silage diet.

However, if the level of magnesium in the grass silage is very low, which is the case on many farms this spring, then even the top-of-the-range dry cow mineral will not be enough to achieve the target amount of magnesium. Supplementation with cal-mag or sweet cal-mag may be required.

Dry cow minerals need to be applied directly on to the silage at the feed barrier. If lack of feed space is an issue, the quantity should be split and fed twice daily. They should not be mixed with silage in the diet feeder. The reason for this is that, in the few days leading up to calving, a cow's feed intake can reduce by up to 50pc. If the dry cow mineral is mixed in with the silage, then, by default, if the cow is eating less silage, she is also eating less pre-calving mineral. Don't forget about the cows in the calving pens. They too need daily dry cow mineral before calving.

Some farmers will feed a small amount of concentrate to cows pre-calving. It is important that the calcium level of the concentrate is very low. If a post-calving nut is fed for example, the high calcium content of it will make milk fever much more likely.

Body condition score management plays an important role in milk fever prevention. Over-fat cows are at a much greater risk of developing milk fever. Steps should be taken to ensure that all cows calve down "fit and not fat".

It can be useful to seek veterinary advice regarding calcium supplementation at calving for over-conditioned cows. A calcium bolus at calving and again 12 hours later can help in older cows or cows that are very much over-conditioned. There are a number of products available that claim to prevent milk fever by controlling DCAB (dietary cation-anion balance). These should be used with extreme caution and only under veterinary and nutritionist advice.

It is worth being aware that moving a cow when she is in active labour can disrupt her progress. This is why it is very important to move a cow to a calving pen before she begins to show signs of calving.

In the case of the cow that had "forgotten how to calve", we managed to get a live Friesian heifer calf out - just.

Blood samples from three more cows on the point of calving were analysed in the clinic the following morning, all of which showed sub-optimal magnesium levels confirming subclinical milk fever. A few small and inexpensive changes were made and, thankfully, the problem seems to have been rectified.

It is only the beginning of what promises to be a very busy spring. Timely intervention based on the right advice can save a lot of hardship.

Eamon O'Connell is a vet with the Summerhill Veterinary Clinic, Nenagh, Co Tipperary

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