Bacteria Counts 101

From Somatic Cell Counts (SCC) to bacteria counts to component testing, the multitude of tests to be performed on milk samples seem to be endless. At times, SCC may seem like the end-all be-all for milk quality, yet there are many more tests used to determine quality and the pay price on your milk check. Bacteria counts—on raw, pre-incubated, and lab pasteurized milk—are tests performed by the Novi laboratory to help determine milk quality. Here’s what you need to know about these bacteria counts, what they mean and how you can improve your results:

Raw Bacteria Count – RBC

Overview: RBC is also sometimes referred to as PLC or official. Prior to testing, milk samples are maintained at 32 to 40 degrees Fahrenheit and then tested on the BactoScan. The BactoScan is an instrument that electronically measures the bacteria levels in milk.

Testing frequency: Once per month minimum, tested more frequently by request.

Premiums: Premium of 5 cents per cwt. is added if raw result is equal to or below 10,000 Colony Forming Units (cfu) per millimeter (mL). There will be a deduction of 10 cents per cwt. for a raw result greater than 100,000 cfu/mL. For more information on premiums, see page 33. The required test performed each month is also a regulatory test. The bacteria count for each producer is shared with the Michigan Department of Agriculture and Rural Development as a requirement of holding a Grade A permit. It is illegal to sell milk with a RBC greater than 100,000 cfu/mL.

Ways to improve results on the farm: High RBC results can be related to poor cooling in the bulk tank; warmer temperatures allow bacteria to multiply faster than cooler temperatures. Dirty milking equipment can also impact these counts. It is also important to ensure udder prep is satisfactory. On rare occasions, a cow can shed enough bacteria in her milk to elevate this count, these cows can be identified by a high SCC.

Excellent Good Warning Action Needed
1,000-5,000 cfu/mL 5,000-10,000 cfu/mL 10,000-50,000 cfu/mL 50,000 cfu/mL and above

Pre-Incubated Count – PIC

Overview: To perform this test, the milk sample is pre-incubated at 55 degrees Fahrenheit for 18 hours prior to testing it on the BactoScan. The 55 degrees Fahrenheit incubation is an optimal growth temperature for psychrotrophic (cold-loving) bacteria. An elevated result could indicate the presence of a spoilage organism.

Testing frequency: Once per month minimum, tested more frequently by request.

Premiums: Premium of 5 cents per cwt. is added if PI result is equal to or below 20,000 cfu/mL.

Ways to improve results on the farm: Hot water used for Clean In Place (CIP) milking equipment should be 160-180 degrees Fahrenheit at the faucet, as milking equipment cleanliness is critical to achieving a good score on this test. Key places to check for cleanliness of milking equipment include: receiver, milking claws, inflations, swingline and bulk tank. The bulk tank should also be cooled to less than 40 degrees Fahrenheit within one hour of the end of milking. Elevated temperatures allow bacteria to multiply more quickly. Poor udder prep can elevate bacteria levels as well, be sure to check the filter sock after each milking shift, a clean sock with little debris will reflect adequate udder prep.

Excellent Good Warning Action Needed
1,000-5,000 cfu/mL 5,000-20,000 cfu/mL 20,000-100,000 cfu/mL 100,000 cfu/mL and above

Lab Pasteurized Counts – LPC

Overview: The LPC is the number of bacteria per ml of milk which survive laboratory pasteurization at 143 degrees Fahrenheit for 30 minutes. Thermoduric bacteria can survive pasteurization because they have developed mechanisms to resist heat and other lethal agents such as sanitizers. Most of these bacteria have an ability to create a protective shell called a spore making it very tough to kill. When looking at the results in the mailer or on the MMPA website, this test is referred to as “PAST.”

Testing frequency: LPC tests are performed by request of the member. Several customers also request/require LPC results on all members serving their facility.

Premiums: LPC is not a regulatory test and there is currently no premium for LPC results.

Ways to improve score on the farm: Prevent higher LPC results by checking the rubber components of equipment, such as milk hoses and line gaskets, for cracks and cleanliness. Any leaky gaskets should be replaced immediately. As rubber parts age, cracks start to form and bacteria collects in those cracks. Overall cleanliness of equipment can also improve results. Extended milking time of eight hours or more can lead to higher LPC results because the longer milking period creates a warmer environment for bacteria to multiply quickly. It is important to change the filter sock every four to five hours and perform at least two complete washes every 24 hours.

Excellent Good Warning Action Needed
less than 10-30 cfu/mL 30-50 cfu/mL 50-200 cfu/mL 200 cfu/mL and above


This article was originally published in the January/February 2022 issue of the Milk MessengerSubscribe »