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This article was published in 1950
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Use of Benedict's Test as a Diagnostic Aid in Entero-toxaemia of Sheep

E. J. McBARRON, B.V.Sc., Inspector of Stock, Albury.

For some time the writer has been applying Benedict's Qualitative Test for reducing substances in urine as a diagnostic aid in suspected cases of Entero-toxaemia in sheep. In a limited series of cases a correlation appears to exist betwen glycosuria and this disease: until sufficient numbers have been investigated it would be unwise to suggest that a specific relationship exists. An increase in blood sugar in cases of Entero-toxaemia has been reported from Colorado (1942-3) and other references have been seen to the same effect. It is thought that other field officers with better oportunities for applying the test may feel inclined to do so, especially when it can be carried out conveniently in the field with little equipment.

Materials.

(1) A supply of standard Benedict's Qualitative Sugar Reagent.—

Copper sulphate 17.3 grams.
Sodium citrate 173.0 grams.
Sodium carbonate 100.0 grams.
Distilled water to 1000.0 mls.

This reagent is stable and will keep for long periods.

(2) A supply of 6in. x ⅝in. test tubes and a spirit lamp. It is an advantage to mark the test tubes at the 5 ml. mark in order to measure out the reagent correctly in the absence of a graduated measure.

Procedure:

Eight (8) drops of urine are added to 5 mls. of the reagent and the mixture boiled vigorously for two minutes and allowed to cool. A negative result is indicated by a clear solution, whilst positives vary from red, yellow or green colourations with precipitates. A bluish-green turbidity is of little significance and is best classed as negative.

Most text-books give the following figures as percentage reducing substances in urine in comparison with the colours and precipitates obtained.—

Light yellow precipitate and supernatant green or blue fluid — less than 0.2%.
Orange precipitate with faint blue or green supernatant fluid — 0.5%.
Orange-brown precipitate — 1.2%.

Fallacies and Precautions. (1) A reduction is likely to occur if albumin is also present. This may be detected by boiling the top of a column of the urine and adding a few drops of 3% acetic acid solution. A persistent white precipitate is indicative of albumin — the Heat Coagulation Test. The albumin is removed by boiling and filtration except when present in very slight amounts.

(2) In herbivorous urine held overnight it is not unusual to find a heavy precipitate in the container. This also occurs within the bladder itself if the cadaver has been subjected to rapid cooling. The precipitate redissolves on heating and is usually due to inorganic carbonates. This requires to be filtered off before proceeding with the test; though its presence may not affect the Benedict's reaction.

Remarks.

Most cases of Entero-toxaemia seen in the field show a distended bladder filled with urine. As such, the collection of the material is not difficult. Jetter and McLean (1943) in considering chemical analyses on post-mortem material found that at 37°C. urinary sugar destruction is about 50% in the first twelve hours after death, with an additional loss during the subsequent 12 hours. This factor must be considered in relating the results of the test with the time after death. Since a period of eight hours after death, under normal seasonal conditions, is sufficient to obscure post-mortem findings in Entero-toxaemia, it is improbable that any chemical tests on body fluids would yield reliable information after that period. There is the further possibility that desquamation of the bladder epithelium would introduce protein material into the urine and affect the test.

Experiments to date have indicated that reduction of Benedict's solution does occur in frank cases of Entero-toxaemia. It is rare that the orange-brown precipitate is obtained, but mostly the orange and green colourations. Examination of the urines of sheep obtained post-mortem from cases of tetanus and heavy worm infestations have returned negative reactions.

References:

Ext. from Ann. Rpts. Agric. Exp. Stat. Colorado, 1942-3. abs. Vet. Bull. Weybridge (1945). 15 : 411.

Jetter. W.W., and McLean, R. (1945). Amer. J. clin. Path. 13 : 178-185. abs Vet. Bull. Weybridge (1945 ). 15 ; 17.

 


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