Grass Tetany by André Voisin

CHAPTER 17

Anatomical lesions in the victims of tetany

SUMMARY
The anatomical lesions most frequently observed in autopsies on cows that have died from grass tetany are degeneration of the liver, hypertrophy of the adrenal glands (which may be accompanied by severe tumours) and calcification of the kidneys and other tissues.

Granulo-fatty degeneration of the liver

An anatomical lesion regularly observed in animals that have died from tetany is granulo-fatty degeneration of the liver.
The principal "metabolic disorder" responsible for this "anatomical lesion" appears to be functional overloading brought about by the conversion to urea (or other nitrogenous substances) of the excessive amounts of ammonia produced in the rumen by very young grass. CHARTON 1 considers these hepatic lesions to be constant but variable according to the stage of development of the disease.2
Although veterinarians in most regions are of the opinion that this degeneration of the liver is common in bovine victims of tetany, there are some areas, nevertheless, where it has only rarely been observed.3 The fact remains, however, that in regions with a high incidence of grass tetany, butchers buying cows from farms affected by the disease consider it highly probable that the livers will be useless. This is an opinion held by interested practical men and will carry some weight.
In conclusion, let it be noted that this fatty degeneration of the liver in bovine victims of grass tetany can lead to hepatic upsets of some severity. The bilirubin content of the blood serum may increase and the onset of tetany is sometimes accompanied by jaundice.4

Severe hypertrophy of the adrenal glands in cows that have died of grass tetany

The mineral imbalance of the ration, particularly too high a potassium : sodium ratio, will be seen to lead to hypertrophy of certain layers of the adrenal cortex. This "adaptation" syndrome may be succeeded by an "exhaustion" syndrome, that is, by degeneration of the a ena cortex.
Twenty years ago, at the National Veterinary School, Alfort, MOUTAUX, assisted by DRIEUX, observed hypertrophy and serious degeneration of the adrenal cortex in cows that had died from grass tetany.5 He concluded that the adrenal gland was affected by a cancerous tumour,6 but there is no justification for generalization on this point.
Twenty years later ALTEN confirmed this finding and established that, in cows suffering from tetany, the adrenal glands are in a state of "hyper-function", manifested on autopsy by hypertrophy of the cortex of the adrenal bodies. CHARTON, for his part, in 1960 reported degeneration of the adrenal glands in bovine victims of tetany. In 1961 it was reported from Holland 7 that examination of 28 cows that had died from tetany had revealed that they were suffering from degeneration of the adrenal cortex accompanied by the formation of vacuoles.

Deposits of calcium in the renal tubules of cows suffering from tetany

Magnesium deficiency has been said to cause calcification of different tissues. Thus, in cows that have died from tetany, deposits of calcium have been found in such soft tissues as the heart 8 and muscles. The calcification is particularly obvious, however, in the kidneys.
Almost all investigators have found large deposits of calcium in the renal tubules of cows that have died from hypomagnesaemic grass tetany, be it spring, autumn or winter tetany, and even in the case of that special tetany caused by green corn. This obstruction of the renal tubules by calcium, due in the main to magnesium deficiency, has been said to be a considerable factor in upsetting the metabolism of the mineral elements, particularly potassium.9

Various post-mortem observations

The following different anatomical lesions have also been observed in cows that have died from different types of hypomagnesaemic tetany:
(a) hypertrophy of the spleen;
(b) degeneration of the nerve cells and neuroglia;
(c) various cerebral lesions (chronic meningitis, encephalomacia, cerebral atrophy, etc.).

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Notes



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  1.  
He describes these lesions as follows:
    
       
 "The attack on the hepatic parenchyma starts with a granular degeneration
discernible only on microscopic examination; this lesion, in fact, is rarely 
determined because, by reason of its reversibility, a cure can easily be 
obtained and, in addition, the clinical signs are discrete. Fatty 
degeneration follows, giving way, at a more advanced stage, to necrosis. 
These lesions are always found in post-mortern
examinations of animals that have succumbed to such necroses. In pure,
 uncomplicated ketosis, on the other hand, with discrete nervous symptoms 
but no disturbance of the calcaemia, the liver presents only an overload 
of fat: neither degeneration nor necrosis is present." * 
    


    

    
 

  2.  
GLAIZE reports having observed such lesions in cows that died from grass 
tetany in the north of France.
    
In the U.S.A. MARSHAK reported fatty degeneration of the 
liver in cows that had died from hypomagnesaemic tetany accompanied by 
hypocalcaemia caused by  undernourishment. * 
    


    

    
 

  3.  
See, for example, the contradictory reports from the Nord department of 
France (which is seriously affected by grass tetany). * 
    



    

    
 

  4.  
This jaundice is characterized by the yellow colouring of the mucosa of the 
eye, mouth and nose. A fairly well-known jaundice is that caused by bitter 
lupin which contains a lupinotoxin. * 
    


    

    
 

  5.  
At Stockholm Veterinary College GARM also observed hypertrophy of the
       adrenal cortex in cows suffering from milk fever. * 
    
       
       


    

    
 

  6.  
It was a case of adrenoma covered with haemorrhagic patches and a multitude 
of calcareous specks. * 
    


    

    
 

  7. 
Observed by SYBESMA. * 
    


    

    
 

  8. 
Various observers, in the case of bovine victims of tetany, have 
reported cardiac lesions such as haemorrhage, oedema and degeneration 
of the myocardium. It should be borne in mind that DE GROOT noted marked 
alterations in the electro - cardiogram of cows that had suffered from 
hypomagnesaemia. * 
    
       


    

    
 

  9. 
In the case of cows suffering from grass tetany these renal upsets can also 
lead to the presence in the blood serum of excessive quantities of 
non-protein nitrogen (urea). *