On New Zealand farms, our high reliance on large amounts of pasture during the early lactation diet actually presents the biggest challenge for calcium management. This pasture supplies very high levels of potassium, normally in excess of 3.0% in fact, when the cow’s nutritional requirement is only in the region of 1.1%. The large over-abundance of potassium doesn’t just compete with calcium for uptake, it also seriously effects the acid/alkaline balance of the blood. Increased pH in the blood interferes with the release of the hormones required to control calcium balance. High blood pH effectively stops the release of parathyroid hormone.

Over the years, farmers have used many strategies to treat milk fever in their dairy herds with varying levels of success. Many of the common strategies used have shown very inconsistent results, and methods that prove successful in one situation can often fall totally on their face in another.

Here is a run-down on common methods to combat calcium deficiency in dairy cows:

• Reducing the levels of calcium in the diet

This is probably the most common method used over the last 40 years. This system can work well as long as no pasture is fed, however to work well pasture needs to be almost totally removed and replaced with a feed that has low calcium, potassium and sodium. Maize silage is one of the few feeds that fits this criteria and where large quantities of maize silage have been added to the diet this approach has worked well. It is however important that these cows are very well supplemented with additional calcium during lactation, otherwise the induced calcium deficit can have serious consequences.

• Injectable calcium

Calcium boroglucinate has always been used as the last line of defence for this disease. This formulation floods the bloodstream with readily available calcium, along with boron, which further increases the absorption of the calcium.

In desperation some have adopted this method as their primary means of control, simply treating the cows showing clinical symptoms being given either by IV, or under the skin. This approach never works satisfactorily. While a bottle of calcium boroglucinate usually gets a cow back on her feet, often times the same cow will go down again later. In many cases when she does seem to recover, she will remain sub-clinically calcium deficient throughout much of the early lactation.

Another issue is that large numbers of subclinical cases of calcium deficiency are not picked up, it can be common to have anywhere between 25 to over 50% of cows suffering sub-clinical calcium deficiency at calving and well into early lactation. As well as producing less milk these cows will be more susceptible to mastitis and uterine infections, as well as poor reproductive outcomes.

Interestingly a number of scientists are reporting (J Wilms et al 2019) that injecting calcium solutions can seriously interfere with the cow’s ability to balance her calcium status longer term, struggling to regulate and control their calcium metabolically in subsequent seasons.

• Flooding the body with calcium in the form of lime flour

Another option that has gained some traction over recent years is the idea of flooding the cow with calcium in the form of lime flour (sometimes with the added option of adding large quantities of vitamin D). This approach can work on some farms however, success is very reliant on keeping the levels of ongoing calcium supplementation very high. This can be challenging with lime flour supplementation. If the levels fall below an often poorly defined point the cow will then be metabolically incapable of activating any of the calcium reserves in her body.

The high levels of lime flour have the added disadvantage of buffering the blood pH to the point where parathyroid hormone release can no longer be activated. This approach means that you are now relying solely on the body’s ability to absorb its calcium from the diet, yet due to the pH bu