This article is prompted by recent discussions on one farm where they were struggling with regular Cobweb problems. The hygiene regime was generally of a very high standard and all operations seemed to be carried out most diligently. Despite this, problems continued.
I recalled phrases I have previously used during hygiene talks; "Are you doing what you think you are doing?", also; "Are others doing what you thought they were doing?" One can add; "And accurately?". Everyone seemed to be on the ball but something was amiss.
There had to be some serious "hole" or weakness in the system. Note that this farm did not have a steam cook-out facility. We considered ventilation ductwork, net, growing room and casing machinery disinfection.
Net disinfection and ventilation ductwork treatments were quickly assessed and modified appropriately. I remained deeply suspicious of growing room and casing machinery disinfection. A bell rang in my distant memory when the farm pressure washer was mentioned. As a grower I had once experienced great difficulty in calibrating and setting the dilution rate of disinfectant through a pressure washer. We would check the accuracy of the farm's machine.
The plan was to fill a 25 Lt drum with the output solution and to note the draw off from the disinfectant supply tank in the process. This would enable the dilution rate to be measured. The exercise proved informative.
Firstly, operator A set the adjustable control valve at X whilst operator B set it at Y.
Sometimes the disinfectant tank was filled with 100% disinfectant. On other occasions (cost was a consideration) the tank was filled with 50% disinfectant. First off, this was all too "iffy"! An equally alarming fact was discovered. It was noted that the disinfectant take off continued at the same rate whether the machine was on or completely switched off! When off, the disinfectant was being siphoned onto the floor and when the machine was in use, a significant amount of disinfectant similarly ended up on the floor (rather than into the output solution). It was thus impossible to calibrate the unit and this would be a worthless exercise as one could not have a situation whereupon a significant amount of expensive disinfectant would end up on the floor.
Perhaps there was a leak that could be repaired. Even if this could be done, one would remain reliant upon the quality and reliability of the needle valve on the disinfectant control and previous experience suggested it would be unwise to do so. With this in mind plus the other "iffy" factors, an alternative arrangement was suggested.
The machine would suck from an exterior tank rather than being supplied from the mains. A 200 Lt drum could be set up for this, into which the exact required amount of disinfectant could be added (and initially stirred with the pressure washer output). This would be done.
Note that the growing room and casing machinery treatments may well have not been effective. It will be interesting to note future disease counts as the amendments filter through the system.
I would not suggest that everyone's pressure washer suffers similar inaccuracies but it may well be worth checking out. Similarly, it is often worth reviewing hygiene arrangements to make sure that procedures have not changed with time. Regarding the cost consideration, it is important that one can set dilution rates exactly so as to incur minimal costs (see graph). There will be a nominal rate for a particular disinfectant and this is generally OK for the treatment of cleaned items. On some occasions it is appropriate to move to a higher rate particularly where organic matter is present. Another occasion would be for example, the disinfection of a growing room with an already wet floor. If there was disease spores in the room prior to cleaning, many of these could now be on the floor after settling. If one then uses a supposedly correct disinfectant solution for the operation, this will then mix with the water on the floor and the dilution will be weakened. The situation would be worse if the dilution was originally below nominal. In summary, one should ensure that all procedures are being carried out correctly and accurately at a minimum cost whilst remaining effective. Is it time for a review?
I hope not to preach as I read that there are already too many other mad preachers about these days.
