The antimicrobial effect of the lactoperoxidase-thiocyanate-hydrogen peroxide system has been recognised in milk and other biological fluids. In this study the main object was to determine whether the inclusion of 10% rapeseed meal (RSM) in layers' diet could enhance the levels of the thiocyanate ion (SCN-) in eggs to a level required by the LP system to promote bactericidal activity in egg products. Twelve 'Abor Acre' pullets were divided into two lots, separately housed and maintained under similar conditions. One lot was fed on a basal diet and the other on an experimental diet containing 10% RSM. Both diets were of known composition, isoenergetic and isonitrogenous. Throughout the feeding trials (15 weeks) a record was kept of egg productivity, individual egg weight and layers weight. Subsequently, the weekly lots of eggs were analysed for thiocyanate ions (SCN-) by gas chromatography. The colour of each yolk was measured using the 'Roche Colour Fan' and organoleptic assessments were made for the detection of trimethylamine taint since the feeding of RSM has been reported to influence these factors. No significant difference was recorded in the average weight of eggs obtained from both groups. However, egg production was 15 % higher with RSM fed hens which lost a little weight. No taint was detected in either set of eggs and no significant variation in yolk colour was noted. After 4 weeks the levels of SCN-reached 1.6 mg kg-l in the experimental eggs and then remained almost constant. The control set had an average of 0.5 mg kg-1 SCN-. Hence an enhancement of the SCN-levels can be achieved in shell eggs by incorporating 10% RSM in the layers' diet. This enhancement is of the order claimed necessary for the operation of this system.

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The free thiocyanate ion (SCN-) content of eggs from five different strains of hen was determined by gas chromatograph as cyanogen bromide after treating the deproteinised liquid whole egg with aqueous bromine solution. Interference by cyanide and residual protein after deproteinisation with phosphotungstic acid was not found to have any noticeable effect on the results. Samples spiked with known concentrations of SCN-gave recoveries of 95%. The levels of SCN-detected ranged from 0.54-0.675 mg kg-l. There was very little variation in the levels detected from one strain of hens over a period of 10 weeks. The amount present presumably originating from the detoxification of cyanide in the liver and kidney would be insufficient to promote bactericidal activity, when incorporated into the lactoperoxidase/thiocyanate/hydrogen peroxide antimicrobial system.