When identifying milk quality issues, a standard plate count (SPC) test isn’t enough. Elevated SPC could indicate dirty equipment, poor cooling, contaminants from the environment or a variety of other issues.

Engel keith
Dairy Farm and Hygiene and Supplies Specialist / GEA

While an SPC test can tell you when bacteria levels are high in raw milk, it can be difficult to identify where the problem is coming from. It’s like getting a grade on your report card but not receiving any indication on why you got that grade.

Incorporating additional milk quality tests into your regular testing schedule can help narrow down the source of elevated bacteria levels to quickly resolve any issues.

‘The Big Four’ quality tests

Testing for lab pasteurized counts, preliminary incubation counts and coliform counts, in combination with your regular SPC tests, can provide a more comprehensive milk quality diagnosis:

  • Standard plate counts (SPC), also called plate loop counts (PLC), provide an overall measure of bacteria quality of milk. Elevated SPC could mean inadequate cleaning of equipment or cooling, worn maintenance parts, improper milking hygiene or a variety of other reasons.

    Use additional quality tests in combination with the SPC test for more accurate diagnostic tools.

  • Lab pasteurized counts (LPC) provide a benchmark to measure organisms that may survive pasteurization. If you have a high count, it’s most likely an indicator of improperly cleaned or sanitized equipment. An LPC test can be an early indicator of a problem before you receive a high SPC test and can also be a great indicator that a problem has been fully corrected.

  • Preliminary incubation counts (PI) measure the number of bacteria growing at cool temperatures, which may be a signal to check sanitation and cleaning of the milking system. A high PI count can also be a measure of improper cooling of milk, rubber goods that need replacing, debris or poor udder hygiene.

  • Coliform counts (CC) measure the number of coliform bacteria in raw milk and provide an estimate of bacteria originating from manure or a dirty environment. A high CC test can indicate dirty cows and milking equipment, contaminated water or poor milking hygiene.

Although historically some milk processing plants only test for SPC, more and more plants and milk quality laboratories are now conducting LPC, PI and CC tests. If you are not currently testing for these counts, consider requesting them from your processing plant or outside testing facility.


Running all four tests on every pick-up is ideal for tracking milk quality. At a minimum, tests should be run twice a week with additional testing requested when problems arise.

Troubleshooting milk quality

Once you receive your milk quality test results, the question becomes what do you do with the information? If test counts are high, the first thing to do is ensure proper cleaning and sanitation protocols are followed and the six requirements of cleaning are met (time, temperature, water volume, chemical balance, velocity and drainage).

Something as simple as a missed wash cycle or low wash water temperature can result in high test counts. Also, reviewing maintenance schedules to ensure equipment is regularly updated can help stop issues before they happen.

Have standard operating procedures in place, and ensure wash cycles are properly functioning to help control test counts and prevent future issues. With the right procedures in place, issues can be corrected quickly so milk quality premiums aren’t lost.

Sometimes a high test result isn’t an easy fix. If you are running proper cleaning and sanitation protocols and still receiving a high test count, it can indicate a bigger issue. Use your milk quality tests collaboratively as a diagnostic tool to pinpoint where issues are coming from.

For example, a high SPC test could indicate any one of the four main causes of elevated bacteria levels – dirty equipment, improper cooling, environmental contaminants and infected udders. But a high SPC along with tests indicating a high PI count and a low LPC and CC would pinpoint the problem as an issue with your cooling system.

Refer to Table 1 as an easy tool to understand and diagnose milk quality issues.Compare quality counts to troubleshoot

Click here or on the image above to view it at full size in a new window.

Maintaining low quality counts

“The Big Four” quality tests are excellent tools to troubleshoot milk quality issues when they arise. However, the goal should be to have consistently high-quality milk and low test counts year-round. Proper on-farm cleaning and sanitation, as well as regular maintenance, can help keep test results in check and boost milk quality premiums.

A simple step you can add to the milking routine is to perform a parlor walk-through at the start of every wash cycle. A quick visual check can help ensure everything is working correctly and catch any issues early. Also, monitor wash cycle temperatures since water temperature is critical for properly cleaned equipment.

Use a thermometer to periodically check the ending wash temperature to verify you are meeting temperature requirements of 120°F or above for proper cleaning and sanitation.

Testing of SPC, LPC, PI and CC, as well as proper sanitation and regular maintenance, can help you diagnose and correct milk quality issues. Work with your equipment and hygiene specialists to perform routine evaluations and keep your milk quality counts on track.  end mark

PHOTO: Following proper cleaning and sanitation protocols can help keep milk quality issues in check. Photo provided by Keith Engel.

Keith Engel