Cows infected with Mycoplasma mastitis do not always shed enough of the pathogen for it to be detected in a bulk-tank sample.

According to Larry Fox, college of veterinary medicine at WashingtonStateUniversity, infected cows shed at low levels about 30 percent of the time. During this time, it is unlikely that a bulk-tank sample could detect mycoplasma in the herd. That means more frequent testing may be warranted.