Detection of Abnormal Milk with Impedance Microbiology Instrumentation

Mastitic milk was detected by obtaining conductance measurements using an impedance microbiology Bactomatic 120 SC instrument. Conductance readings separated normal and abnormal milks after 30 min at 25°C when readings differed by more than 2 to 3% and exceeded the variance among instrument module wells. Samples blended from four quarters of a cow indicated milk from one quarter was abnormal if the salt level in the abnormal quarter raised the blend conductivity above that of normal samples and variance among the wells. Either solid or liquid substrates that contained stimulants could be used to accelerate bacterial acid production or reduce impedance detection times and did not affect the ability to detect abnormal milk. However, measurements varied with the volume of sample in the well, suggesting that fixed 1-ml liquid volumes of milk be used. Such volumes would allow detection of abnormal milk and bacterial load on the same sample.