By now you may have seen that preliminary incubation count (PIC) for raw milk is not just a laboratory recreational activity, but it is a number that affects your milk price. The fluid milk processing industry has recently taken a big interest in this number because it believes two things: 1. PIC is a good predictor of shelf life, and extending shelf life reduces the milk dumped from store shelves.

2. PIC can be reduced with better management practices at the farm.

In some cases, milk handlers – even those sending the majority of their milk to cheese plants – have incorporated PIC into their premium programs.

What is PIC?

The bacteria count is determined by incubating your milk sample at 55ºF for 18 hours, then plating it and performing a Standard Plate Count (SPC). The number of bacteria present are then estimated. The PIC (18 hours) is compared to the regular SPC, which is a bacteria count when the sample is fresh. The idea is that bacteria that grow in the udder do not grow well at 55º, but certain bacteria that originate outside the udder can. If PIC is high compared to SPC, it suggests some undesirable practice on the farm allowed these bacteria to enter the milking equipment and grow somewhere between the milking unit and the bulk tank.


According to Cornell University Food Science researcher Kathryn Boor, the goal for PIC is less than three to four times the SPC, or less than 50,000. While Dr. Boor notes PIC is useful for troubleshooting equipment cleaning practices, she says there is no scientific evidence of association of PIC with product shelf life.

Why PIC may be high

The following reasons for high PIC are taken from a Virginia Extension publication:

•slow cooling farm bulk tank or temperature above 40°F (bulk tanks should be less than 40°F within two hours of milking and kept below 45°F during subsequent milkings); this points out the importance of the recording thermometer and its use

•failure to thoroughly clean equipment after each use or neglecting to sanitize equipment before using (a major cause)

•problems with debris build-up in plate coolers and chillers

•when milking fresh cows and problem cows in bucket milkers, hoses need to be kept clean

•dirty animals; may need clipping

•poor udder sanitation practices (dirty, excessive water used to wash teats and udders); teats need to be clean, sanitized and dry

•contaminated water supply, especially coliforms or other spoilage-causing bacteria

•washwater temperature should start at 155 to 170°F and drain at above 120°F

•gaskets and rubber parts need to be clean, free of cracks and deposits, and replaced when necessary

•improperly drained milking equipment

•teat cup liners should be clean and free of cracks and changed on schedule

•pulsator and main vacuum supply lines need cleaning on a regular basis and especially whenever milk enters the line

•Streptococcus agalactiae or environmental streptococcus mastitis infection PD

References omitted but are available upon request at

—From Lewis County Ag Digest, Vol. 13, No. 2