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
"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.