40+ years ago, cows were not drenched with magnesium at all. However farmers are now being advised to drench with magnesium until zinc dosing starts in late January, due to suboptimal blood Magnesium levels. And this is despite continuous drenching! Why has this come about?

To answer this, we first need to clarify what causes grass staggers, or hypomagnesaemia.

 
Hypomagnesaemia is often loosely described as a deficiency of magnesium in the blood. Technically this occurs when Magnesium loss through milk production is higher than the amount absorbed into the bloodstream from feed. Many cows may be suffering from hypomagnesaemia but not displaying any obvious symptoms – these symptoms won’t appear until animal is truly deficient in magnesium, and include mild tremors, low body temperature, staggers and frequent falling over.
 
Note: In the scientific name for this condition, ‘hypo’ indicates deficiency, ‘magnes’ indicates magnesium and ‘aemia’ indicates that it relates to the blood: hence, blood magnesium deficiency – interesting fact for the day!
 

With that said, why are we drenching with magnesium so much more?

In the 1970s, it was estimated that New Zealand soils were losing 15kg of magnesium per hectare per annum due in large part to unsustainable fertiliser applications having a negative effect on soil microbial populations. With less magnesium in the soil, the amount of magnesium found in pasture has also reduced and therefore so has the amount ingested by production animals. Rather than nurturing the microbial life in our soils to help improve Magnesium levels and availability, we are now using Magnesium drenches as a substitute.
 

The real problem…

 
Although ever decreasing amounts of Magnesium in the soil is an major issue, a more pressing problem could be considered to be the unavailability of this magnesium – i.e. the Magnesium isn’t getting from the soil, to the pasture, to the animal.
 
Inefficient fertiliser applications on many New Zealand farms have resulted in a loss of active clover and nitrogen fixing bacteria in root nodules and in soil. These Nitrogen fixing clover and bacteria are vital for ensuring the availability of Magnesium, Calcium, Potassium and Nitrogen to the plant. When these minerals aren’t found in correct quantities in the plant, this raises ammonia levels in the rumen which decreases the ability of the animal to absorb Magnesium into the bloodstream.
 
Another factor affecting the availability of Magnesium to the plant is high Potassium levels in the soil. This problem is often aggravated by further reduced Magnesium absorption in the animal due to the Potassium to Sodium ratio being out of kilter.
 
When you combine this lack of availability with the decreasing amounts of Magnesium in our soils, it’s no surprise that many cows are struggling to absorb sufficient amounts into their digestive and production systems.

The Solution   There is no quick, magic cure for preventing grass staggers. What you will need to do is nurture the microbial population of the soil so that those little bugs and bacteria can process the fertiliser you are applying and make it available for plant uptake. Ensuring your mineral applications are balanced and are being utilized by the plant will also help to ensure your animals are able to get the minerals they need to stay healthy.   While these steps in a fertilizer programme may not directly improve production, they can dramatically improve animal health which in turn can reduce costs and improve productivity in the long run. The end result is more profitability! If you would like more information about how you can reduce metabolic problems in your herd, please feel free to contact one of our consultants by clicking here.