Due to the poor quality of much of the forage fed over the winter period to both dairy and suckler cows we could see an increase in the incidents of Grass Staggers (Hypomagnesaemia) on any farm across the UK when stock are turned out at this time of the year.

Due to the poor quality of much of the forage fed over the winter period to both dairy and suckler cows we could see an increase in the incidents of Grass Staggers (Hypomagnesaemia) on any farm across the UK when stock are turned out at this time of the year.

As previously reported the feed value in grass and maize silages and hay have been down, due to the poor weather conditions throughout 2008, resulting in stock coming out of the winter in less than ideal overall condition.

Many spring calving dairy and suckler cows will be being turned out onto lush grass with a high water content that is low in magnesium, as well as other essential nutrients, the outcome of which will be that incidents of grass staggers will increase, especially in lactating animal where high levels of readily available magnesium are particularly important.

Equally important is the newly lambed ewe, which can also be at risk when there is a flush of wet grass of questionable nutrient quality.

Ruminants are particularly vulnerable because only about 2% of the total magnesium in the body circulates in the blood; this is the only source of magnesium available for immediate use even though the total amount of magnesium in an adult cow is about 200g. However, 70% of this magnesium is locked in the skeleton and is therefore unavailable. In the lactating animal a further 28% is required within the tissues of the body for normal metabolic processes involved in milk synthesis, making a massive demand on these reserves.
It is important to remember that magnesium cannot be stored in a readily available form that can be utilised immediately. Any excess in the diet is excreted in the urine. Therefore ruminants require a continuous supply of magnesium in the diet, as the 2% available within the blood will only buffer a dietary deficit for a short period of time.
Magnesium is actively transported across the rumen wall and there are a number of factors affecting this process. It is an energy dependent process in which sugars have been shown to improve magnesium absorption, whereas high levels of ammonia in the rumen and low salt levels in grass and the diet overall, can depress magnesium absorption, this latter point being especially relevant in wet conditions. During cold wet, windy conditions grazing time will be curtailed which will reduce DM intake and with it magnesium intakes. Moreover, these poor environmental conditions also cause stress, which can result in the increased urinary excretion of magnesium.

An imbalance in nutrients, especially magnesium cannot be avoided in such situations, especially if the grass is the main source of minerals with no additional supplement being on offer.

The application of fertiliser, early on in the season also has an effect, as high levels of potassium can restrict the uptake of magnesium by the grass. High levels of nitrogen (as ammonia) and potassium can also interfere with magnesium absorption in the animal’s digestive system.

Often the first sign of Hypomagnesaemia is sudden death. However, an individual animal may show symptoms before death, she will be increasingly nervous, will shake, walk stiffly and when she collapses her legs and feet will 'paddle' and her head will be held back.

The fact is that although this is often looked at as an individual problem it needs a whole herd/flock solution.

Any incidence will mean that magnesium levels are low in the entire group, with only one or two animals, in the first instance, exhibiting major symptoms. In other group members there will be evidence of sub-clinical disease, they will be increasingly nervous, they may become difficult to handle, milk production will be lower and there may be weight loss.

Millions of pounds are lost to the industry, every year, through the incidents of grass staggers and the deaths caused by it. The costs are surprisingly high when the methods of preventing the disease are so easy to introduce and so cost effective.

As adult cattle and sheep are unable to store an easily available form of magnesium they are totally dependant upon dietary sources to satisfy their day-to-day requirements and to meet any sudden increases in demand especially at times of stress. Therefore, ideally they should have continually available a palatable sources of magnesium, preferably with a source of energy (in the form of sucrose) to aid absorption and access to salt, low levels of which can also depress magnesium absorption in the rumen.

Neglecting an animal’s requirement for magnesium at high-risk times during the year can be expensive and yet the problem can be so easily solved by making magnesium available in the most appropriate form to all ruminant stock, either as liquids, as a continuation of those fed over the winter, solid molassed tubs or by including magnesium at enhanced levels in bagged minerals.