Hazell Mullins: Clinical Milk fever cases are only the tip of the iceberg

I remember vividly in my days in vet school in Nottingham, in which milk fever/Hypocalcaemia based lectures always contained an image of an iceberg floating ominously in the ocean.

The image is now ingrained in my memory and illustrates that the clinical cases, or the downer cows on farm, were only the smaller tip of the iceberg and the hidden base represented the subclinical cases.

Despite the subclinical disease usually meaning silent disease, it doesn’t mean that these cows don’t give us clues to their low calcium status and go completely unnoticed in the herd. 

They can present with many secondary issues such as retained after-births, mastitis cases and a little later after calving with left displaced abomasum (LDAs), which may require surgery. 

The research shows that for every one case of a downer cow with milk fever, there are another four to five cases of subclinical milk fever in the herd hence the iceberg being the perfect symbol. 

Last spring, I took a lot more investigative bloods on farms where these issues were a concern from cows 24-48 hours post calving, and it was a great way of diagnosing the issue of subclinical milk fever and took the guesswork out of the equation.

Thankfully, milk fever can be preventable on farms with a combination of timed calcium boosters and dietary manipulation. Calcium demand at calving skyrockets due to the demand for colostrum production going from 10g to up to 50g, so giving calcium at this time of high demand can be a benefit.

During the week, my dad, Anthony, reminded me to order the calcium-rich fresh cow drink that we give to all our cows the minute they calf. A friend of mine, Donal O Callaghan, once likened the hast that the cows drink these fresh cow drinks to “that first pint after lockdown”. I personally think it’s the “tea and toast” of the cow maturity ward. 

They have the added bonus of rehydrating the cow after the fluid loss during calving and encourage feed intake, which ensures more calcium intake. 

Boluses can also prevent cases of both subclinical and clinical milk fever however, timing is crucial. When you see the pin bones soften and she is at the point of calving this is the time to bolus and then again 24 hours later, however, this is dependent on the brand used, so always read the instructions.

Every year on the farm, we have cows that we watch more closely for milk fever signs as they are at higher risk. Our cow, 1028, an older high-producing Holstein-bred lady, is one that jumps to mind straight away. 

I have flashbacks of treating her last year in the early hours of the morning with a bottle of Calcium IV after I spotted her stretched out on the calving camera. Unfortunately, she had not received a preventable calcium bolus that evening before calving, and due to the hour she calved, she didn’t receive her fresh cow drink either. 

I have learned from my mistakes in this instance, and this spring, we will be more alert to cows like 1028, who now is on the repeat offender list. 

As well as older cows, those who are on their third or more lactation, other risk factors for milk fever include over-conditioned cows (those with a body condition score of more than 3.5), cows scanned in twin, and Jersey-bred cows.

Interestingly, Jersey cows naturally have fewer Vit D receptors that are required for calcium absorption and also higher calcium content in their milk.

The dry cow diet is also key to milk fever prevention, however, to cover this in-depth, this article would resemble a thesis. The main point to consider is the relationship between the minerals; calcium, magnesium and potassium.

The inclusion of at least 20g of Magnesium via the pre-calver mineral and keeping the calcium low is essential to the priming of the cow’s hormones to immobilise calcium from her body reserves when calved.

The presence of potassium in the diet of over 1.8%, acts to bind magnesium and may mean the cow needs more added to her diet. This is why silage sampling is vital to know the level of magnesium required to offset potassium’s effect. 

Magnesium chloride is sometimes added to the diet for this reason, be careful when using it, however, as palatability can be an issue, and feed intakes can suffer as a result. 

Keeping the intakes high for the cow near calving is vital to prevent ketosis, so in preventing one disease, we could induce another. Milk fever prevention via the diet can be complicated at times but involving both your vet and nutritionist can help to formulate the ideal prevention diet.

If you suspect an issue with subclinical milk fever, consult with your vet about running diagnostic blood tests and coming up with both a short-term and long-term milk fever prevention plan.

• Hazell Mullins BVM BVS is a large animal Vet at Highfield veterinary Group.