Grass Tetany by André Voisin

PART I

THE SYMPTOMS OF GRASS TETANY
AND THE LOSSES IT INCURS

CHAPTER 2

Losses caused by grass tetany


The difficulty of finding out how many animals have died from tetany

It is very difficult to assess exactly the loss incurred by grass tetany. In effect:
The farmer himself has difficulty in distinguishing the disease and frequently attributes it to a multitude of other causes. He removes the dead animal from the field and transports it to the knacker's yard without informing anyone at all.
If the veterinary surgeon was called in there was the possibility until quite recently that he would confuse milk fever and grass tetany. As will be seen later, it is very difficult in many cases to distinguish between the two.
Despite all this, recent surveys carried out in various countries have enabled the loss to be determined with greater certainty. Some of the figures obtained will be examined below.

Grass tetany costs French stock-rearers much more than £700,000 each year

France has long kept silent about grass tetany and the methods of farming that promote the disease.
Following the tetany disaster that resulted from the application of these methods in one of our "National Schools of Agriculture" in 1959, it was no longer possible to ignore the facts. An investigation initiated at the time by LARVOR, BROCHART and THERET produced the map of France (Fig. 1) referred to above showing the extension of the area ravaged by grass tetany during the past twenty years.
LARVOR estimated that the number of cases of grass tetany for the years around 1959 rose annually by some 11,000-12,000 cases for the whole of France. The number of deaths due to tetany was 2200, or 19% of the animals affected, which represents a loss of nearly £300,000. But as the present author pointed out in a communication to the Academy of Agriculture of France, these workers, despite their efforts, were able, as they themselves admitted, to locate only a fraction 1 of the animals that died. In addition, animals suffering from tetany frequently remain ill to a greater or lesser degree, and this in itself is very costly. It is no exaggeration, therefore, to say that grass tetany is costing French farmers much more than £700,000 each year at present.

Grass tetany in Holland

Holland, where more fertilizer is applied to pasture than in any other country in Europe or indeed in the world, appears to be the country most affected by grass tetany. It was in Holland, moreover, that the great Dutch scientist SJOLLEMA proved the correlation existing between hypomagnesaemia and grass tetany.
In 1956 'THART estimated that 1-2% of the dairy cows in Holland were attacked by grass tetany each year. About the same time an enquiry reached the conclusion that tetany gave rise to the death of 3000-4000 cows each year and considerably lowered the production of 30,000 more.

Development of grass tetany in Great Britain and Ireland

Great Britain was and still is a country very severely affected by grass tetany. The disease would appear to have begun to develop seriously about 1930. To begin with, it was local in character and was known as "Hereford disease".
In 1955 WITHERS established that 3-10% of the dairy herds in the South of England were affected and that the annual frequency of tetany was 1-5 cases in every 1000 cows. In Scotland in the same year GRUNSELL reported 1-2 cows in every 1000 attacked by grass tetany.
Many surveys have been undertaken in Great Britain in recent years to determine the percentage of animals affected by grass tetany. These were summarized by HIGNETT in 1961 in the statement that 10% of the dairy herds were familiar with grass tetany and that, depending on the year, 1-5 out of 100 cows suffered from tetany. A smaller percentage of cows are attacked by grass tetany than by milk fever or acetonemia, 2 but the percentage of cows dying from tetany is about 30%, which is higher than in the case of acetonemia and milk fever. The percentage reaches almost 100% in the case of ewes; HIGNETT holds the opinion, and with good reason, that in general almost all the ewes attacked by grass tetany die rapidly before any counter-measures can be implemented.
A survey made in Ireland for 1960-61 has revealed that in one year 5000 cows were affected by grass tetany, two-thirds of the cases occurring in the spring.

Grass tetany in Germany

One of the regions most affected by grass tetany in Germany is Schleswig-Holstein. In 1931 WARRINGSHOLZ reported that grass tetany had been known since 1907 in Holstein. In 1960 PETERS records that an average of 10% of the cows in Schleswig-Holstein are suffering from grass tetany and that about 22% of the sufferers die. 3 Ten per cent is a very high figure, but the author nevertheless admits that many of the cows suffering from tetany could not be revealed by the survey and that the actual figure must be even worse. On the basis of this minimum he arrives at the conclusion that the number of cows dying from tetany each year in the province of Schleswig-Holstein alone is worth £140,000. He does not omit to mention that similar enormous losses are incurred by cows suffering from tetany that have been able to be saved: these are animals with poor yields that often have to be disposed of at a low price. The figures can therefore frequently be doubled at least, which means an annual loss of £280,000 in a German province whose area (15,000 km or 6000 sq. miles) is more or less the same as that of Cornwall, Devon and Somerset.
Another seriously affected area of Germany is the Lower Rhineland pastures. NAUMANN, Director of Research for the Chamber of Agriculture, Bonn, has reported that in 1961, which was particularly wet, 4 1073 farms in this area and a total of 1680 beasts were found to be affected by grass tetany.

Grass tetany in New Zealand

As long ago as 1933, HOPKIRK in New Zealand reported that grass tetany had been present for fifteen years or so in the Waikato region and had become more frequent in the course of the last seven years. In 1956 SWAN wrote that in New Zealand's dairying districts one visit out of three paid by a veterinary surgeon was concerned with milk fever or grass tetany. In 1960 SHORTRIDGE stated that although on the whole the percentage of beef breed cows affected by grass tetany was not very high, 20% on some farms might suffer from the disease.

Grass tetany in Scandinavia

Grass tetany was recorded in Denmark in 1931 and has developed greatly in recent years. In Norway it is found on farms practising intensive grazing management.

Grass tetany in the United States

It will be seen later that the United States suffers from a special tetany: one that affects animals grazing green cereals. particularly green corn, in winter. Ordinary grass tetany does occur, however, especially spring grass tetany which is generally the most serious.
A survey carried out in 1959 revealed that in certain counties of West Virginia, with different soils, however, 1-4% of beef suckling cows were stricken each year by tetany. Certain farms were particularly affected, and 10% of the cows in a herd sometimes died from the disease.

Grass tetany is a real menace in certain herds

Taken as a whole, grass tetany may not affect a very high percentage of cows, but it can be a real menace in some herds, which it strikes in a manner as spectacular as it is overpowering. At the British Veterinary Association Congress in 1960 a Derbyshire farmer 5 stated that he had lost 16 out of a herd of 50 cows from grass tetany in one year alone. Still in England PATERSON, the owner of a group of 40 herds of dairy cows, reported, over four years, 546 cases, 154 of which had proved fatal. He estimated that 6% of his cows were attacked and 2% died each year.
In Schleswig-Holstein BECKER carried out a study of eight farms on which 20-50% of the cows were stricken by tetany every year without exception.

Tetany causes great anxiety to the farmer

A farmer whose methods of pasture management have created the conditions that give rise to grass tetany is terrified by the thought of finding new animals on his pastures stricken with this "falling sickness", which, until very recently, was still of a mysterious nature so far as many farmers were concerned. Now that he knows that an injection of magnesium salt can often save the animal if it is treated in time, he runs round his fields several times a day checking on his stock so that he can put in an urgent call to the veterinary surgeon, if need be, or give the injection himself. Life therefore becomes impossible for this poor unfortunate farmer.
Another point that makes the disease a particular source of anxiety is that although only a fifth of the animals affected die, a large number remain miserable specimens, their metabolism permanently upset without any hope of ever returning to normal: these are the "metabolic cripples" that rarely find their way to the butcher. Their end is more often the sausagemaker, if not the knacker's yard.
It is understandable, therefore, that in view of the development of the disease over the last twenty years (see Fig. 1) grass tetany has become more and more disturbing despite the relative effectiveness of magnesium injections.




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Notes



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  1. Not forgetting that many of the cases of 
hypomagnesaemic tetany are still diagnosed and classified as 
milk fever. *

    


  2. Metabolic disorder characterized by the smell 
of acetone in the cow's breath. Appears
 particularly when the animals are being stall-fed. *


    
 
  3. In the spring of 1958 grass tetany was particularly 
severe in Schleswig-Holstein. Veterinary surgeons reported having 
treated 9260 cows, 1000 of which died. *


    
       

  4. For the favourising effect of humidity on tetany see 
Fig. 21. *



    


  5.  SALISBURY. *