Grass Tetany by André Voisin

CHAPTER 32

Green wheat tetany (wheat poisoning)


Green wheat pastures in various countries

Having discussed grass tetany on temporary pastures, we will conclude the present Part by examining tetany on a special type of temporary pasture, namely, a pasture of green cereals, and more particularly of green wheat. The grazing of green wheat has sometimes been recommended in Europe. The main cause of anxiety was to find out whether the yield of grain was diminished by this grazing of the young wheat plants. Unfortunately, little or no thought was given to the health of the grazing animal.
Grazing of green cereals, particularly green wheat, is practised on a large scale in the Plains of the southern United States, especially in Texas, Oklahoma, Mississippi, etc. It is also practised in the Argentine, Australia, etc.

Hypocalcaemia and hypomagnesaemia in green wheat tetany

Tetany occurs in rapidly growing green wheat, particularly in wet weather; it attacks cows as well as ewes. It is referred to as "wheat poisoning" or "wheat pasture poisoning".
Comparative analyses have been carried out on green wheat on which there has been no tetany and green wheat on which tetany has occurred.1 Tetanigenic green wheat seems to present the same imbalances as very young grass:
a. very high protein content (248): 20-26 % crude protein in the dry matter;
b. high potassium content;
c. very low sodium content.

Certain workers have observed marked hypocalcaemia 2 (3-0 - 6-0 mg. calcium in 100 c.c. blood serum) in cows suffering from wheat poisoning and have concluded that an important causal factor is a high potassium : calcium (K : Ca) ratio in the blood serum.3
Other workers have noted hypomagnesaemia, with or without hypocalcaemia. There have even been cases 4 of affected ewes with extremely low contents of magnesium (0-5 mg./100 c.c.) in the blood serum.
On the whole, hypocalcaemia would appear to be more marked than hypomagnesaemia.

Hypocupraemia in cows suffering from green wheat tetany

In Kentucky (U.S.A.) GRAINGER studied herds grazing green wheat, many of the cows in which were affected by tetany. Moderate hypomagnesaemia 5 was present with normal calcaemia. The copper contents of the blood serum, on the other hand, sometimes reached the very low levels of 13, or even 8 microgrammes/100 c.c., whereas the lower limit of safety is held to be 60-70 microgrammes.6
In the opinion of the American investigator this hypocupraemia existed in many of the cows attacked by green wheat tetany and was the expression of a disturbance in the copper metabolism. Grass giving rise to grass tetany is frequently low in copper.7

External symptoms and characteristics of green wheat tetany

The symptoms of green wheat tetany are more reminiscent of grass tetany 8 than of milk fever,9 in so far as the symptoms of these two diseases can be distinguished clearly. The symptoms of green wheat tetany may be very similar to those of grass tetany, but they differ from many points of view. Although green wheat tetany can occur in cows accompanied by their suckling calves, it can likewise take place shortly before calving. which is very rare in the case of grass tetany and fairly rare with milk fever.
It is thought that green wheat tetany can take place from the fifth month of pregnancy (i.e. four months before calving) up to the sixth to seventh month following calving. However, 80% of the cases occur in the 60 days following calving, which is similar to the figure recorded for grass tetany (cf. Table 1).

"Physiological conditioning" of animals grazing green wheat

Green wheat tetany takes place between 1 and 6 months after the animals have been grazing green wheat. Eighty per cent of the cases occur 60-150 days after the animals are put on to a grazing of this nature. It appears, therefore, that the relatively rapid "shock" occasioned by spring grass tetany a few days after the animals have gone out to grass is replaced here by a "conditioning of the animal", resulting from the disturbance of certain of its metabolic functions. This corresponds with grass tetany, in which underfeeding predominates. This "physiological conditioning" appears to be confirmed by the fact that the kidneys of animals that have grazed wheat are wasted by calcareous deposits. This disturbance of the renal functions, exactly as in the case of grass tetany, can help to produce convulsions under the influence of the mineral imbalances present in the young green wheat.
Naturally, moreover, there may be some deterioration of the liver and of certain endocrine glands, as in the case of grass tetany.
Further confirmation of "physiological conditioning" appears to be presented by the fact that animals that had grazed green wheat manifesting any pathological symptoms were subsequently attacked by tetany when transported to the market by truck or lorry.10 Cases have been reported where there have been 20-40% deaths in the course of transport.

Therapy for green wheat tetany and protective measures

Special emphasis is placed on calcium salt therapy 11 supplemented by phosphorus and/or magnesium.
It would appear 12 that buccal supplements are often effective 13 as a protection against green wheat tetany:
magnesium salt;
legume forage crops (rich in magnesium);
cotton cake.

It would obviously be of interest to have trials demonstrating the extent to which magnesium fertilizers offer protection against green wheat tetany as they do in the case of grass tetany.

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Notes



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  1.  
       
The amino-acid composition of green wheat has also been compared with that 
of ordinary pasture grass. Green wheat would appear to contain less 
methionine but more lysine. *


    

    
 

  2.  

 The diffusible calcium content of the plasma also falls to the level of 
2-5 mg./100 c.c., which seems to be the danger limit for nervous 
ailments.

A low phosphorus content in the blood serum of affected cows has often 
been established: this can be of the very low order of 1-2 mg./ 100 c.c. 

One characteristic of green wheat tetany is hypoglycaemia, the sugar 
content of the blood falling gradually from the normal values of 
80-120 mg./ 100 c.c. to the low levels of approximately 50 mg./100 c.c.
 *

    

    
 

  3.  

 Hyperpotassaemia is sometimes, but not necessarily, present, they 
believe. On the average the K : Ca ratio (weight) of the blood serum 
would be 3-00 in cows affected by green wheat tetany against 1-50 in a 
normal cow.
    

American workers succeeded in increasing the potassium: calcium ratio in 
cows by means of buccal administration of potassium chloride; but there 
was no tetany. On the other hand, when the calcium content of the serum 
was reduced by intravenous injections of potassium oxalate tetany occurred 
as soon as the K : Ca weight ratio exceeded 2-62. *


    

    
 

  4.  

  The stand being grazed was one of green oats. *


    

    
 

  5.  

 The minimum magnesium content established in the blood serum was of the 
order of 1-04 mg./100 c.c. *


    

    
 

  6.  

 With all the usual reservations surrounding these figures for an 
isolated element, no account being taken of the other factors entering 
into play. On the question of copper in the blood serum, see 
Soil, Grass and Cancer (pp. 34-40). *


    

    
 

  7.  

 Note that the blood serum, whether of ewes or cows affected by green 
wheat tetany in this part of Kentucky, had a high content of bilirubin, 
which indicates a disturbance of the functions of the liver. The serum 
also had a high content of non-protein nitrogen, the manifestation of poor 
functioning of the kidney. *


    

    
 

  8.  

 The first symptoms are generally excitement, lack of appetite and lack 
of co-ordination of movements. The animal staggers and falls. It is 
subject to muscular convulsions. It frequently grinds its teeth and 
salivates a great deal. It flickers its eyelids, and its eyes seem to be 
staring out of its head. This period of extreme agitation (generally 6-10 
hours) is followed by a state of coma, from which time it is too late to 
treat the animal.
    

As in the case of grass tetany, the temperature rises, and may exceed 
102.2° F. (39° C.). *


    

    
 

  9.  

 Post-mortem examination of animals that had died from green wheat tetany 
revealed  small haemorrhages on the surface of the heart and small cysts 
in the kidneys. Microscopic section of the kidneys revealed that the renal 
tubules were more or less bulging with calcium deposits. Magnesium 
deficiency, which exerts a marked influence on calcium metabolism, is 
known to cause deposits of this nature in the renal tubules. The result is 
that the urinary excretion of mineral elements, especially potassium, 
is thrown out of gear. *



    

    
 

  10.  

 For tetany in transport, see Chapter 36. It will be seen that grazing, 
in certain cases, appears to create a pre-disposition to transport tetany.
 *

    

    
 

  11.  

 Intravenous or intra-peritoneal injections of 50 c.c. 17% calcium 
gluconate are administered. The intra-peritoneal injection can be given 
more rapidly. *



    

    
 

  12.  
 Barrentine.  *



    

    
 

  13.  

 These were ewes with very marked hypomagnesaemia and normal calcaemia.
 *