The bulk tank milk culture has long been the standard method for screening dairy herds for the presence of contagious mastitis pathogens (Streptococcus agalactiae, Staphylococcus aureus or Mycoplasma).
Whenever these bacteria are present in a bulk tank milk sample, it is concluded that there are infected mammary glands in the herd. Because these mastitis pathogens are intermittently shed into the milk, single day bulk tank samples are not reliable indicators of the absence of contagious mastitis infections. However, research has shown when 3 or more consecutive daily bulk tank samples are taken and pooled for culturing, test results are dependable.
The bulk tank milk culture is also recognized as an excellent monitor of the effectiveness of pre-milking teat prep. Since most environmental mastitis pathogens found in bulk milk generally do not come from infected mammary glands but rather from the teat surface, it is reasoned that whatever environmental bacteria (coliforms and non-ag streps) not removed from teat surfaces during pre-milking teat prep will then end up in the bulk tank milk.
Thus, the level of environmental bacteria in bulk tank milk samples is a direct reflection of the effectiveness of pre-milking teat prep. As in the case for contagious infections, pooling multiple days of bulk tank milk samples will give a more representative assessment of pre-milking teat prep across days and milking shifts (see Quality Count$ Fact Sheet FC-MC-1).
Many research studies indicate that production of high quality milk with minimum mastitis and optimum milking speed requires consistent cleaning of teat surfaces (including teat ends) and correct machine attachment timing (see Quality Count$ Fact Sheet F-MR-4 - Principles of Ideal Pre- and Post-milking Cow Prep). A survey of milking protocols will yield numerous pre-milking teat prep methods all hoping to achieve clean dry teats.
A lot of the pre-milking teat prep protocol variation is due to housing and milking equipment differences as well as personal preference and inconsistent application of pre-milking prep procedures by milking personnel.
Recent introduction of robotic milking and such things as mechanical teat scrubbers has challenged the more conventional DIP - STRIP - DRY and APPLY teat prep protocols. But regardless of your teat prepping procedure method, the expected outcome must be the same – CLEAN, DRY TEATS.
The bottom line is pretty simple: If the numbers of coliforms and non-ag strep bacteria on your bulk tank culture results are high, you are NOT getting teat surfaces clean enough!