by André Voisin
Translated from the French by
CATHERINE T. M. HERRIOTT

CHARLES C THOMAS - PUBLISHER
BANNERSTONE HOUSE
301-327 East Lawrence Avenue, Springfield, Illinois, U.S.A.

Published simultaneously in the British Commonwealth of Nations by
CROSBY LOCKWOOD & SON LTD 


 
        Printed and bound in Great Britain

                       by Richard Clay & Co Ltd 

                   The Chaucer Press, Bungay, Suffolk 






         Foreword 
   

    
    by 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 
more poor 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.



       
       
     
 INTRODUCTION 
 




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     CHAPTER I 

       
  
     Modern farming methods favour the
       development of grass tetany 

 

      
       Tetany, the tragic meeting of animal and grass 
 
 

 
    Grazing is the meeting of animal and grass.1


    
       
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.2



   
       
       A case of disturbed magnesium metabolism  

 
      
It was observed almost thirty years 
ago that parenteral injections 3
 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. 4  
 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
5 causes:




	
	
	-imbalance in the composition 6 
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, 7 
 although it is generally particularly prevalent in the spring.

       
Modern farming methods upset the magnesium metabolism of the 
        grazing animal



       
In the course of the last twenty years 
the use of certain 
methods, known as "intensive grazing", combined with excessive dressings 
of mineral and/or organic fertilizers have brought about a considerable 
development in grass tetany. This development concerns spring as well as 
autumn and winter tetany and affects cattle as well as sheep.
 
       
France has been affected relatively 
less than other countries, 
but it can be estimated, nevertheless, that tetany is responsible for an 
annual loss of at least £700,000 to stock-rearers in France. 
This in itself is serious enough, but what gives rise to even more concern 
is the rapid advancement of tetany during the last twenty years. The map 
in Figure 1 illustrates the extent of this development. The upshot is that 
present-day farming methods are giving rise to imbalance in the
soil and herbage which is upsetting the magnesium metabolism of the grazing
animal, with consequent neuro-muscular disturbances which find expression 
in the convulsions of grass tetany.


Figure 1.: Development of tetany in France during the last twenty years. 



      
       The silence surrounding tetany 



       
The character assumed by grass tetany 
has on many occasions been as secretive as it is mysterious. No farmer 
likes to talk about the diseases prevalent among his stock for fear that 
he will have difficulty in selling them.

       
In addition, those who had contributed 
towards the 
spread of tetany by their bad counsel made every possible effort to have 
the disease minimized or even ignored. The author was stimulated to write 
this book, therefore, in the hope that this disease, which strikes a herd 
suddenly like a curse, without mercy and without warning, might be better 
understood. And its publication seemed all the more essential, as grass 
tetany furnishes general information of considerable importance.



       
A book on grass tetany is destined for readers with very different 
backgrounds



       
Publishing a book on grass tetany 
unfortunately presents 
a host of difficulties. A work of this nature must primarily outline 
practical means of avoiding grass tetany, in which case it is addressed 
to the practical agriculturalist. But the agricultural adviser and 
veterinary surgeon, although also interested in the practical
aspect, want more information about the metabolic disturbances in the 
animal organism that trigger off the convulsions of tetany. The physiologist
also wants to know more, and will ask why these metabolic disorders prevent 
normal nerve-muscle transmission.

       
Despite the present inadequacy of our 
chemical knowledge regarding 
these questions, it is essential, therefore, in this book to survey certain 
scientific aspects of the metabolism and physiology of the animal: or, to 
be more exact, to investigate the danger of our farming methods upsetting 
the neurohormonal 8
 equilibrium of the animal at grass. Such chapters may 
dishearten the practical man, and for this reason a short summary is 
provided at the beginning of each which may be sufficient for the 
non-specialist. An attempt has also been made to keep such chapters as 
few and as short as possible, at the risk of being reproached by the 
specialists for not dealing with certain subjects in sufficient detail or 
even for not mentioning certain theoretical problems at all. The
numerous footnotes supplementing the basic text are aimed at specialist 
readers in particular, in an attempt to compensate for inadequate attention 
to the scientific aspects of grass tetany.

       
Be that as it may, all readers, 
specialist or otherwise, are advised in their first reading to concentrate 
on the basic text, omitting tables, figures 9 
and footnotes.
Subsequently, according to their knowledge, they will be able to study the 
whole text of the chapters that interest them particularly.



       
 Start from empirical knowledge to 
arrive at theoretical causes and in this way improve our practice 




A particular obstacle stands in the 
way of such a book. Although many of the physiological causes of grass 
tetany are still unknown, adequate information is now
available concerning practical methods of "protection" 10 
against grass tetany,
methods that will be discussed in the last part of the book. The whole book 
has therefore been designed with the last part in mind, and this means that
 only those physiological phenomena will be dealt with that justify and 
explain the practical methods of protection against grass tetany 
available.

       
It is generally said that practice is 
only applied theory. This is frequently incorrect, particularly in 
agriculture. Farmers' incredible powers of observation have succeeded in 
developing empirical methods that are often remarkable.
Agronomic science must try to explain these traditional methods 
scientifically. 11 
From this theoretical knowledge information can then be 
deduced which will enable time-honoured farming methods to be perfected 
in practice.

       
This has been the aim in the present 
book.





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Notes



[Click on asterisk (*) at the end of a note to return
 to the point you left in the text]


      

          

  1. For this definition see  
Grass Productivity *


    

  2. As the Normandy farmers so nicely 
put it "the fire of the grass has been too much for the animal". *


    


  3. Introduction of an element into 
the organism by some other route than the digestive
       tract, e.g. by intramuscular or intravenous injection. *


    


  4. This is hypomagnesaemic tetany, 
one of the many forms of the disease, and one
       which will be dealt with in this book. *


    


  5. In addition to which there are 
several internal and some other external causes which
       will be dealt with in Part VII. *


    


  6. Mineral or organic. *


    


  7. Lack of balance in the composition of the 
herbage seems to predominate in the spring, but the two effects can be 
superimposed on each other in all types of tetany in any season. *


    


  8. Or neuro-endocrine. The endocrine 
glands are the internal secretory glands such as the thyroid, adrenal 
glands, etc. *


    


  9. The presentation of the text is 
always such that it can be read and understood without reference to the 
tables and figures if the reader so desires. *


    


  10. A distinction is made between:
    

      

    1. "preventive" and prophylactic medicine which represents the 
various hygienic measures together with the use of vaccines;

    2. "protective" medicine, the aim of which is to maintain in perfect 
condition the metabolic mechanisms of the individual cells or 
their ensemble as represented by the complete organism.

    
The various aspects of this question are dealt with in Soil, Grass and 
Cancer. *


    


  11. Science is still far from success.
 For example, we are still able to provide only a poor explanation of the 
regeneration of fallow soil, although this method has been used for
more than 2000 years by the farming "empiricists" of Europe. *