Sampling Schedule
The bacteriological status of mammary quarters was
determined at the initiation of each study by the collection and culture of duplicate milk samples 1 wk before
bacterial challenge was initiated. A third sample was
collected from specific quarters and cultured when results from the first two samples differed. Milk samples
were collected and analyzed bacteriologically during
each week of the study. Whenever Staphylococcus
aureus or Streptococcus agalactiae were isolated for the
first time in a previously uninfected quarter, a second
sample was collected and cultured within 48 h to con-
firm the new IMI. All quarters were eligible for new
IMI caused by Staph. aureus or Strep. agalactiae except
those quarters infected with organisms of the same
species as challenge organisms and those with deformed or abnormal teats.