viewpoint

March 2015

with John Barnes – Managing Director

March 2015
There has been quite of lot of discussion regarding science and making sure we have a science based fertiliser programme. I am in favour of this as we should all be very careful about what we apply to our soils. Over the years many well respected scientists have led the way into many of our farming problems. In my own life time we have gone from scientists telling us we don’t need selenium to the now accepted practice of the wide use of this element. Quite rightly this is the way we learn and grow.

There are times when a previous generation have found answers to problems, but then the next generation either forgets or chooses to not follow on with those answers. It is not my role or intention to comment on what others may be thinking but to give you some information that has been out there from well-known and respected scientists from around the world and also from New Zealand.

I came across a book by André Voisin. He was a French scientist who wrote extensively some 60 years ago. As is always the case, a lot of the information is great with some of it being rather interesting. As the traditional season for magnesium applications approaches, here are some extracts from his writings on magnesium and the effects of its lack or imbalance on animals.

 Grazing is the meeting of animal and grass.

This meeting may be happy or unhappy; it may even be tragic, as in the case of grass tetany, a disease characterized by convulsions which attack mainly (but not exclusively) grazing female ruminants (cows, ewes, goats, etc.). It can occur at any time of the year, but is particularly frequent in the spring when the animals go out to grass.

The disease appears to have been always in existence, because long before mineral fertilizers were in use farmers in many regions farming rich soil or applying large quantities of liquid (or semi-liquid) manure to their pastures were familiar especially when they turned their stock out to grass in the spring, with what they called “grass paralysis”, a condition they attributed to the “fire” of the grass in the full vigour of its growth.

A case of disturbed magnesium metabolism. 

It was observed almost thirty years ago that parenteral injections of a magnesium salt were sufficient in many cases to stop the convulsions of grass tetany, in the same way as injections of calcium stop the convulsions associated with milk fever. The blood serum of many animals suffering from grass tetany was also found to have a lower magnesium content. The conclusion was therefore drawn that grass tetany was due to magnesium deficiency. This is not strictly correct, because the word “deficiency” necessarily implies a “lack” of magnesium in the ration, which is not inevitably or always the case. For this reason, therefore, we prefer to say that grass tetany is due to a disturbance of the magnesium metabolism which can have two main external causes:

• imbalance in the composition of the herbage leading to direct or indirect magnesium deficiency;
• Under-feeding, with the consequent ingestion of inadequate quantities of magnesium.

Given these two causes, grass tetany can take place in any season, although it is generally particularly prevalent in the spring.

Having spent a lifetime in the farming scene, I have observed both the benefits and the difficult side of work with the land. This year is no exception. We are experiencing low commodity prices and yet another weather event. It would be great if we could just have a few years to have great pay outs and a bumper season coincide so debt could be paid off and books can be balanced. But life is not like that, therefore we continually need to have the attitude of our forebears with the can do attitude. Attitude is so important…

 W. R. WOOLDRIDGE, PH.D., M.SC., F.R.C.V.S., F.R.I.C. 
Scientific Director,
The Animal Health Trust

Grass Tetany, a metabolic disorder of ruminants, has been recognized for about 100 years. Although the overall incidence is not high it is a spectacular disease which may result in several animals, which were apparently normal when last seen, being found dead in the field a few hours later. It is thus of considerable economic importance to the individual farmer. Because grass tetany is associated with the ley type of farming and particularly with the use of large amounts of fertilizer rather than with the more traditional type of permanent pasture farming, the disease is encountered mainly by the modern progressive type of farmer. As more and poorer quality land is improved by reseeding with grass strains low in magnesium, such as rye grass, and the use of fertilizers, it can be anticipated that the incidence of grass tetany will increase unless adequate steps are taken to prevent disease.

It is only within the last 30 years that workers in the Netherlands associated the disease with a decrease in the amount of magnesium in the blood of affected animals. During this period much research work has been designed to provide an explanation of the disease. Although a great amount of information has accumulated and many of the factors which can increase or diminish the incidence of the disease are now known, the exact mechanism which causes it is still the subject of much discussion.

One of the most active workers in this field has been André Voisin, and it is therefore very helpful to have a book compiled by him reviewing available knowledge obtained from both scientific investigations and practical experience.

Cattle most frequently develop grass tetany soon after they are moved from a diet of hay and concentrates to rapidly growing young pasture. Such a change in diet frequently results in a decreased intake of magnesium which is often a contributory factor to the development of the disorder. One of the effects of heavy applications of fertilizer, particularly potash, to pasture is to decrease the magnesium content of the grass, and it has been clearly shown that such applications of fertilizer increase the incidence of grass tetany. On the other hand the application of magnesium salts to pasture decreases the incidence of the disease. Research work has shown, however, that other factors must also be concerned, because grass tetany can be produced following a change in diet which does not alter the dietary intake of magnesium. It is generally agreed that the animal cannot absorb magnesium as efficiently when fed a lush grass diet as when on a hay and concentrate diet.

It would appear from this short description of the disorder that it could be avoided with efficient management. As is indicated, however, the decision as to what is efficient management will vary with the environment and conditions governing the keeping of the animals and hence a book which reviews the subject as widely as does this present volume by Voisin will prove invaluable to all who are interested directly or indirectly in grass tetany.

W. R. WOOLDRIDGE
9th September, 1963.

Isn’t it interesting that there are new problems which we face today which have been dealt with by others years ago. In fact Cornelius Peter During (known as Peter During) who graduated from Massey College (now Massey University) in 1949 wrote about magnesium deficiency and suggested adequate levels that should be both in the soil and in the leaf.

Following on from this Hills Laboratory added another report to their Herbage Test Report called the Animal Dietary Mineral Balance Report which reports not only on the elemental value of the pasture but also how your stock will react either positively or negatively to the pasture. If all is well then the farmer can relax. If there is a problem then clearly remedial action needs to be taken.

At Fertilizer New Zealand we tend to be proactive and work towards taking action prior to problems arising. However there will be times when for unforeseen reasons something will show up and we can provide remedial solutions. Magnesium products are available from many suppliers and most of them work well. All will have some limitations. Many will be sold by companies with a vested interest. Fertilizer New Zealand don’t have an alliance with any magnesium trader, rather we will provide magnesium products which will meet your needs.