The chance of a no color change occurring because of contamination with disinfectants or cleaning agents is only possible in case of high concentrations. When such agents are correctly used for disinfection and or cleaning of milking equipment or teat disinfection, the final concentration in the milk is too low to interfere with the test performance.
However, at incorrect use in general, Delvotest® microbial inhibition tests can be inhibited by such compounds. See table below.
Preservatives, used to preserve milk for later analysis, could make the milk unsuitable for testing or will significantly prolong the required incubation time.
Indicative concentration of example disinfectants and cleaning agents giving a positive Delvotest® result at control time (1 ppm = 1000 ppb = 1000 μg/Kg)
Active chlorine
200 ppm
Iodine
150 ppm
Hydrogen peroxide (30%)
600 ppm
Quaternary Ammonium Compounds
30 – 10000 ppm
Mercuric chloride (corrosive sublimate)
10 ppm
Potassium dichromate
20 ppm
Sodium Azide
50 ppm
Published: 10 November 2025
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