Dairy Cattle in Mississippi
Preliminary Incubation Count
Preliminary incubation count (P.I. count) is being reported by many of the milk marketing cooperatives as an indication of milk quality. Still, some producers are not aware of what the count means or how it is determined. The standard plate count (S.P.C.) for bacteria is still being used by the Mississippi Health Department for regulatory purposes. On the other hand, the P.I. count can give a dairy producer valuable information for maintaining high quality milk.
To determine P.I. count, the raw milk sample is incubated at 55º F for 18 hours. This is similar to holding raw milk for 48 hours prior to pasteurization. Bacterial results below 50,000 per ml are acceptable, but the goal should be 20,000 or less per ml. Many results will be less than 10,000 per ml, just like the S.P.C., if sanitation is good.
Causes of high P.I. counts include poor udder preparation techniques, slow cooling or bulk tank temperatures above 40º F, failure to thoroughly clean milking equipment after each milking and neglecting to sanitize equipment before use.
