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DISEASES CAUSED BY ORGANIC POISONS: UREA, ACIDOSIS, PHOSPHATE

by C.F. BATH

Middelburg, CP

 


UREA POISONING

Urea is used as a source of nitrogen, which can be converted to protein in cattle and sheep, and is usually given in the form of a lick. Most cases of poisoning are caused by faulty formulation where too much urea is added. Other cases are caused by the lick being too readily edible - soft crumbles and liquids with plenty of molasses are particularly dangerous. It has also occurred when hard licks have been wetted by rain and sheep have subsequently drunk the liquid, which contained large amounts of urea.

The rumen adapts to converting urea to protein, and so sheep, which are accustomed to licks, can consume much more without ill effect than those which are abruptly put on a ration containing a "safe" amount of urea.

 

SYMPTOMS AND POST-MORTEM

Shortly after consumption the urea is converted to ammonia, which gives rise to the typical symptoms seen. Animals shiver, stagger, breathe rapidly and die within a short time after violent convulsions have set in. Sheep which have taken lesser amounts of urea may survive, but sick sheep may still be dying 7 days after consumption of urea.

At post-mortem, haemorrhages and watery swelling of the intestines, and froth and water in the lungs are the main lesions seen, Haemorrhages may occur elsewhere in the carcass.

 

TREATMENT AND PREVENTION

A weak acid will neutralise the ammonia in the rumen. The most practical antidote for the purpose is ordinary vinegar (acetic acid) and about half a bottle per sheep may be given.

To prevent poisoning, great care must be taken in making up the lick. Only hard blocks protected from rain should be available. Sheep should gradually become accustomed to taking the full amount and should not be put onto the lick when salt hungry. Because of the inherent dangers, valuable animals should not be given urea, but rather a safer source of protein. One such source is biuret, which is non-poisonous even when eaten far in excess of recommended strength. Alternately these animals must be given vegetable or animal meals, such as peanut oil cake meal or carcass meal, to supply the necessary protein in the ration.

 

ACIDOSIS OR GRAIN OVERLOAD

The rumen of a sheep is normally adapted to digesting mainly cellulose, which occurs in grass and bushes. Only small amounts of grains such as maize, wheat and oats can be digested without difficulty by sheep that are unaccustomed to these grains. The rumen can, however, slowly adapt to digest up to 60 - 80 per cent grain in the total ration, if grain is increased gradually over the period which should normally be at least 6 weeks.

If there is too sudden an increase in grain in the total ration, particularly in sheep which are completely unaccustomed to it, the rumen is unable to cope and this results in the disease known as acidosis.

Carbohydrates (starch) in the grain are converted rapidly to lactic acid, and the balance within the rumen is destroyed. The pH (a measure of acidity) drops from around 6,5 to 5,0 and lower. Water is drawn from the body and this causes dehydration; at the same time the acid-base balance within the body is disturbed and body fluids become more acidic.

There are several ways in which this grain overload may occur. First of all the ration may be altered too quickly, so that there is not enough time for adaption. Secondly, sheep may suddenly come across meal through carelessness of a worker. Examples are the door to a grain storeroom being left open, or several days' supply of grain being put out at once instead of daily. Thirdly, sheep are often put onto croplands which, for various reasons, have not been reaped or have been incompletely reaped. This is often the case after a frost or disease has made reaping worthless. Under these conditions the sheep eat large amounts of the grain and go down with acidosis. Hungry sheep will always be more exposed to danger as they will eat far more. It is quite possible for other sources of starchy or sugary carbohydrates to be responsible for acidosis. Overeating reject raisins, for example, will cause a very similar disease.

 

SYMPTOMS AND POST-MORTEM

Diarrhoea, consisting of a greyish, sour smelling porridge-like matter, is usually present, although initially it is often absent. Animals become weak and may be unable to stand, and the eyes are sunken due to dehydration. The rumen is often distended, which gives the appearance of bloat.

At post-mortem a suspicion of acidosis may be formed if the rumen contains a large amount of watery of doughy grain, particularly if it has a sharp, sour smell. The rumen and intestines are usually reddened and the latter contain a greyish pasty or watery matter.

The condition is confirmed by measuring the acidity of the rumen.

 

TREATMENT AND PREVENTION

The chief objective of treatment is to return the acidity of the rumen and body to normal. Sodium carbonate, aluminium hydroxide and magnesium oxide have all been used with success. In severe cases sodium bicarbonate must be given intravenously. Removal of the contents of the rumen by a surgical operation is often lifesaving, so it is advisable to summon the help of a veterinarian without delay.

It is obviously preferable to avoid the condition by strictly controlling access to grain as outlined above.

 

PHOSPHATE OVERLOAD

Although phosphate is an essential part of the diet, if too much is given it can lead to the formation of deposits in the bladder (gravel or stones). Normally calcium content is greater than phosphorus content in sheep rations, but if too much grain (especially oats) is supplied, and especially if phosphate is supplied in addition in the form of monosodium phosphate, this ratio is reversed and phosphorus content exceeds that of calcium. This often happens to rations which are fed to stud rams being prepared for sales, since the farmer is trying to get them into peak condition. The excessive amount of phosphates cannot be utilised by the body and are excreted in the urine, where under the right conditions they crystallise out as a salt. In ewes this does not constitute a problem, but in rams and wethers, where the urinary canal is long and restricted, these aggregations can block the canal and so cause death due to kidney damage and poisoning of the body with waste products.

It must be emphasized that this is a specific type of gravel or bladder stones, which only occurs in rams or hamels on this type of diet. Other forms are due to water or plants eaten in the veld, and the exact cause and mode of formation in most cases is unknown.

 

SYMPTOMS AND POST-MORTEM

Symptoms only set in once blockage has occurred. Grinding of the teeth, frequent straining and panting are the outstanding symptoms. There is often blood or pus around the sheath, which is either dry or may drip small amounts of urine. The penis is frequently dark red due to inflammation. As the condition progresses the animal strains more and more, sometimes the whole skin moves with the effort. If the ram is touched just below the anus, he will be very sensitive and start straining.

If the urinary canal bursts, urine escapes under the skin and causes swellings around the penis and into the scrotum.

Eventually the animal weakens and dies after 2 to 6 days.

At post-mortem the carcass is watery and smells of urine. Frequently there is urine in the abdomen as the bladder has burst. The bladder is often very inflamed and bloody, and contains greyish, soft, crumbly crystals. If the urinary canal is opened, the same matter will be found blocking the canal. The kidneys are swollen and watery.

 

TREATMENT AND PREVENTION

If the blockage is promptly relieved by operation, the animal should recover. It seldom happens that the blockage is spotted soon enough, and in most cases irreversible damage has already occurred by the time the sheep can be presented for treatment.

Prevention is quite simple: rations fed to sheep must not have a calcium to phosphorus ratio of less than two to one. Rations in which the ratio is not known must be analysed to determine it, and all constituents must be considered. (This includes licks, blocks and water). No phosphate lick or phosphate in the water should ever be necessary in sheep fed this type of high energy, high protein ration.

Addition of agricultural limestone to the ration is recommended to rectify any imbalance present, but the amount will depend on the extent of the imbalance.

 

Published

Leaflet : Wool production E 6.4 / 1975