Grass Tetany by André Voisin

CHAPTER 41

Protective measures on farms affected by grass tetany


Tetany therapy in an animal does not suppress the causes of the disease in the herd

Tetany has struck. The veterinary surgeon and the farmer stand contemplating a cow in convulsions. The surgeon gives an intravenous or parenteral injection of magnesium and calcium salts. As often happens, the cow recovers and is back to normal within a few minutes.
Generally, that is where matters rest. The veterinary surgeon departs. All the farmer has to do is to wait anxiously for the other cases of tetany that will not fail to appear in his herd the next day, or the day after, this year or in subsequent years, because the causes remain.

After therapeutic treatment it is a case of practising "protective" medicine

"Protective" medicine is our concern here. If protection against tetany is to be afforded, the fundamental rule of "protective" medicine must be applied: namely, the animal must be provided with healthy food, produced on healthy soil, that will not upset the metabolic mechanisms of the organism. This is an agricultural problem, as are all problems concerned with the production of foodstuffs that will not impair the metabolism of the individual cells or of all the cells together.
How can this problem of "protective" medicine be solved in the case of grass tetany? Assume that the veterinary surgeon, Smith, has been called in by the farmer, Brown, and has just administered a magnesium injection which has (or has not) stopped convulsions in the first of Brown's cows to be attacked by spring grass tetany.
Whether the cow is saved or not, Smith must make clear to Brown, calling in the local agricultural adviser, if possible, what steps he must take to prevent more of his cows being attacked by tetany in future. These instructions will have to cover three different stages:
1. Immediate and urgent measures to prevent the tetany striking the rest of the herd the next day.
2. Measures to be taken in the course of that same year and the following winter so that tetany does not recur either in the autumn or winter of that year or when the animals are put out to grass the next year.
3. Permanent steps to be taken always so that tetany never recurs.

Immediate and urgent measures

1. Immediately and without delay the animals must be removed from the tetanigenic type of pasture on which the case of tetany has just occurred. They must be taken, without haste or brusqueness,1 into a stall or shed.
2. If the animals exhibit any stiffness of the limbs or muscular tremors,2 they must be given a subcutaneous injection of magnesium immediately.
3. In the stall (or shelter) they must receive, until the next morning, a supplement of:
(a) good hay or, for want of anything better, straw;
(b) about 50 gm. magnesia (MgO) 3 (to be bought from the chemist if the veterinarian has none with him in his car), which will be mixed with wet pulp, crushed oats or barley millings.
4. (a) The next day, and during the two following weeks, the animals must be put out to graze on old, permanent pasture, with some tufts of hard grass, that has received neither nitrogenous nor potassium fertilizers, nor liquid manure. The farmyard can often provide a "safe" pasture of this kind.
(b) Throughout this period hay and magnesium supplementation must be continued. Concentrates containing magnesium and rapidly obtainable can be used.
(c) The cows will spend the night in the stall or under shelter so long as the weather remains cold and does not heat up for a period of at least 6 days. This housing will facilitate the supplementary feeding of roughage and magnesia.
5. If the farm does not have a pasture of this kind and only temporary or permanent swards of very short herbage saturated with nitrogen and potash are available, it is cheaper for a week or two to feed the cows in the stall until the herbage becomes sufficiently long and fibrous. When they go out to grass again, this must be done gradually.4
6. One must be very cautious about autumn tetany in the year of the spring attack. Care must immediately be taken:
(a) Only to graze long grass and to observe sufficiently long rest periods.
(b) If that is impossible, as it generally is in autumn, to "fill up" with hay (or straw) and administer magnesia from the end of September.5
(c) Bring the cows into the stall as soon as the nights begin to be cold.
(d) Apply no nitrogenous or potassium fertilizer in that year.
7. At the end of the year care must be taken that the paddocks which are to be used first the next year are not over-grazed and that some fairly long grass remains.


Measures to take for the following year,6 to protect against tetany

1. Temporary suppression of nitrogenous and potassium fertilizers. The suppression of nitrogenous fertilizer will obviously reduce the production of green material from the sward. But, as has been said before, it is not a case of producing more grass, but of producing more meat and milk to the acre. Tetany cows, even when apparently restored to health, are only capable of reduced performances. Moreover, the appearance of tetany in some animals indicates that the herbage is an imperfect foodstuff which will allow the animals to achieve only low levels of milk and beef production.
2. After liquid manure has been applied, mow the sward and graze only after mowing. Balance the liquid manure by applying the necessary amounts of mineral elements (Table 12).
3. Apply during the winter 2677 lb./acre [3000 kg./ha.] calcined magnesite 7 (containing 87% magnesium (MgO)) and 6 lb./acre [7 kg./ha.], copper sulphate or an equivalent copper slag, and 178 lb./acre [200 kg./ ha.] salt (sodium chloride). These different dressings, if need be, can be limited provisionally to the pastures to be grazed first in the following year.
4. In spring, gradual putting out to grass.
(a) If possible on permanent pastures.
(b) On paddocks that were not grazed bare at the end of the preceding year and contain some hard herbage.
(c) Avoid starting grazing on paddocks that have already produced tetany.
(d) For the first two or three weeks of grazing bring the cows into the stall at night and feed a supplement of 50 gm. magnesia (or a concentrate supplying this amount) and fibrous foodstuffs (straw, hay, etc.).
5. Keep a close watch on the animals. If any exhibit stiffness or spasms, give a subcutaneous injection of magnesium.
6. On paddocks that have previously produced tetany, take a cut, if possible, before grazing.

Measures to suppress tetany once and for all8

When these various steps have suppressed tetany, which generally takes place after 1-2 years, necessary measures must be implemented to ensure that, even with very high pasture productivity, there will be no danger at all of tetany. Many of these are the same as the measures taken in the first two stages of "protection" and have been described in detail in the present chapter or elsewhere in this book. To help the veterinary practitioner, the agricultural adviser and the farmer, however, they may be summarized in the following eleven rules.
1. Apply no potassium fertilizer in winter. On the other hand, apply phosphates and copper sulphate each year in winter.
2. If necessary, apply 2677 lb./acre [3000 kg./ha.] calcined magnesite or other magnesium fertilizer every 3-5 years.
3. If nitrogen is applied before grazing, apply:
sodium or calcium nitrate (Table 9);
nitrogenous fertilizer with magnesium (e.g. Stickstoffmagnesia).

These dressings must be applied very cautiously, if one is not certain that the soil has received sufficient available magnesium. See that the herbage at the beginning of May contains at least 0-20%. magnesium in the dry matter.
4. Gradual putting out to grass on paddocks (permanent grass, if possible) that were not grazed bare at the end of the preceding year. Take the cows indoors at night so long as the nights are cold and wet.
5. During this period of mixed diet at the commencement of grazing, feed the animals fibrous foods (hay and/or straw).
No further supplementation of magnesium should be necessary if all these measures have been implemented, particularly if the necessary magnesium fertilizer has been applied.
6. Distribution of nitrogenous fertilizer dressings over the year. These should be applied as soon as the animals leave a paddock. Use sulphate of ammonia only where:
the soil is too alkaline (pH too high);
the soil has received enough magnesium fertilizer.
After the second rotation, should the soil require it, apply small dressings of potassium fertilizer containing magnesium and, if possible, sodium. (If necessary, sodium fertilizer can be applied).9
7. Between two grazings allow a rest period sufficiently long - and this will vary with the season and weather - for the herbage to grow high enough for grazing.
8. Avoid grazing too much temporary grass relative to permanent grass.
9. If liquid manure is spread, cut before grazing and balance up the liquid manure with dressings of mineral elements (Table 12).
10. Avoid tiring the organism by feeding a winter ration too rich in protein: for example, too much cake or very young grass silage.
11. See that salt licks (sodium chloride) are always available in the stall or in the field.


Special protective measures against autumn and winter tetany

In both winter (including green wheat tetany and autumn tetany, undernourishment plays a particularly important part. Care must be taken that the animals have enough grass. Should herbage become scarce, there must be no hesitation in offering supplementary feeding,10 whether the animals are at grass or under cover.
It is important that this scarce grass that the animals are "harvesting" in the field should have the best possible mineral balance and contain as much magnesium as possible. It is advisable, therefore, that the necessary magnesium fertilizer 11 should have been applied to the soil. This is particularly important in those parts of the world where green cereals are grazed. The other general rules listed above naturally apply also, but it should be added that where flocks of sheep are being transferred from poor hill grazings to rich valley pastures, the change in feeding should be implemented as gradually as possible.

Eliminate the "metabolic cripples"

None of these steps will have any effect on animals that have been receiving the wrong feeding over the years (for example, very young grass overloaded with nitrogen and potash) and have thus suffered injurious effects that have made of them "metabolic cripples".12 This is the case, for example, if the liver or adrenal glands have been irreversibly damaged.
At all events these animals should be culled, for their yields of meat and milk will always be low.

Lack of theoretical knowledge does not prevent very effective practical steps being taken

If these relatively simple measures are strictly applied, there will be no tetany.
Despite our very limited theoretical knowledge on the subject of grass tetany, therefore, it is perfectly possible at the present time to eradicate this terrible disease that is the scourge of so many regions where it causes great loss.

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Notes



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  1. 
 Any nervous irritation runs the risk of triggering tetany in cases where 
it is latent. It is wise, therefore, to shift the stock while the 
veterinary practitioner is still there, so that he can intervene 
immediately, if required. *


    

    
 

  2. 
 Especially after this shifting, which may have triggered these 
pre-tetany manifestations. *


    

    
 

  3. 
 See Chapter 37. *


    

    
 

  4. 
 In the case of winter grass tetany in cows or ewes the measures are more 
or less identical: put under cover, supplementary feeding, buccal 
administration of magnesia. The same is true of autumn tetany. *


    

    
 

  5. 
 Date to be altered depending on local or seasonal conditions. *
      

    

    
 

  6. 
 Or, to be more correct, for the years that follow, until tetany has 
disappeared. *


    

    
 

  7. 
 Or other magnesium fertilizer. *


    

    
 

  8. 
 These measures to put a definite end to tetany on farms where it has 
already occurred are obviously the same for a farm where the disease has 
never occurred, and is not wanted, but where attempts are going to 
be made to increase production by the application of fertilizer and 
rotational grazing. *


    

    
 

  9. 
 If the content of sodium in the dry matter is less than 0-50%.  *


    

    
 

  10. 
 Which naturally can include mineral supplements of magnesium and salt. 
*

    

    
 

  11. 
 If this is necessary, also apply sodium fertilizers. *


    

    
 

  12. 
  See the author's paper "Soil and Metabolism". *