Grass Tetany by André Voisin

CHAPTER 39

The physiological causes of grass tetany


The three physiological causes of grass tetany

Hypomagnesaemic grass tetany is a functional disturbance resulting from several of the metabolic mechanisms being thrown out of gear. These upsets can be the outcome of three broad categories of physiological causes:
1. Nutritional.
2. Internal causes stemming from the animal organism.
3. External causes, the result of the animal's environment.

Nutritional causes

It is probably the nutritional causes that assume the main role in hypomagnesaemia. The tetany Linder study is grass tetany, which indicates the dominant part played by nutritional factors inherent in the herbage.
A simple nutritional cause of hypomagnesaemia is under-feeding. In the case of grazing this means that the quantity of dry matter "harvested"1 by the animal is inadequate. This may be due to the fact that:
(a) herbage is not present in the pasture in sufficient quantity;
(b) the grass, by its unbalanced composition, causes digestive upsets that reduce the animal's appetite.

In addition, the unbalanced composition of the organic matter in young grass leads to the presence of excessive quantities of ammonia (Fig. 15) in the rumen, with the following probable consequences:
1. Reduced magnesium resorption in the digestive tract.
2. Increased content of ammonia in the peripheral blood (Table 20).
3. Reduced magnesium content in the blood serum (Table 20).
4. "Wear and tear" on the liver, which thus loses some of its capacity for rapid conversion of ammonia to urea (and other nitrogenous substances). This helps to raise the ammonium content of the peripheral blood, not to mention various other physiological disorders.
5. Production of various toxic, nitrogenous substances such as histamine).

Magnesium deficiency, chronic and moderate, causes calcification of the kidneys, which are henceforth able to carry out their functions only imperfectly.
The excess of potassium in the herbage, combined with a very low content of sodium, throws the adrenal cortex out of gear, an upset characterized principally by the secretion of an excess of aldosterone, which can contribute towards hypomagnesaemia.
The excess of potassium gives rise to increased secretion of adrenalin, which "sensitizes" the animal to tetany.
All these mineral imbalances in the young grass combine to upset neuromuscular transmission, with consequent tetany convulsions.

Internal causes within the animal itself

The functioning of the metabolic mechanisms of an individual can be determined by hereditary characteristics, and it is possible that certain breeds or lines may be more susceptible to tetany than others.
The functioning of the metabolic mechanisms, however, also depends on the previous "dietary record" of the animal, starting from the very date when it was conceived. It has just been seen that a diet that causes excessive quantities of ammonia to be produced in the rumen exhausts the liver, which will probably have difficulty in rapidly converting the excess ammonia produced in the rumen by very young grass, thus facilitating the tetanigenic effects of the latter. It has also been said that:
1. sodium deficiency leads to degeneration of the adrenal glands;
2. magnesium deficiency causes calcification of the kidneys.

The previous action of these dietary factors, combined with hereditary characteristics, determines finally the "physiological susceptibility" of the animal to grass tetany.

External factors affecting the animal

External factors appear in the main, but not exclusively, to assume a "triggering" role with regard to convulsions in the hypomagnesaemic animal.
One of the main factors is a low temperature followed by a sudden rise in temperature (see Fig. 20). Wet conditions accentuate this effect (Fig. 21).
Any excitement (noise, fear, excessive physical effort, etc.) can trigger convulsions in the hypomagnesaemic animal.

| Go To Chapter 40 | 



| Grass Tetany Table of Contents |



| Home |
Ag. Library |
Health Library |
Sovereignty Library |









      

Notes



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




     


    

    
 

  1. 
  See Grass Productivity, pp. 67-86. *