Preliminary Incubation (PI) counts are an important indicator of milk quality on dairy farms. While we typically see high somatic cell counts spike in the summer, it’s during the winter months when PI counts can creep up. High PI counts often point to issues such as inadequate hot water during equipment cleaning, poor cooling practices, or contamination during handling.
The PI count reflects the cleanliness of equipment and cows, and dairy producers should aim for a PI count of under 10,000 CFUs/per milliliter.
Here are some key areas to check if struggling with high PI counts:
1. Udder cleanliness: While typically we see somatic cell count issues with dirty teat ends, ensure you’re using a proper teat-tip, and be sure to wipe each cow with a single-use towel or paper towel.
2. Rubber parts in milking equipment: Rubber parts such as gaskets, hoses, and liners, need to be adequately cleaned, air-dried, and changed on a routine schedule. Cracks within the rubber parts can harbor bacteria, causing increased PI counts. Remember to replace inflations as well.
3. Wash cycle hot water temperature: Having adequate hot water is especially important this time of year, during the winter months.
a. The water temperature for the rinse cycle should be between 110- 120°F. If the water is too hot during this cycle, it could result in a protein film on the surfaces of the equipment. Water that is too cold could result in the milk fats crystallizing and leaving behind a greasy, hard-to-wash surface on the pipe walls. Ninety to 95% of all milk residue should be removed during the rinse cycle. There should be clear water running out of the diverter when this cycle has finished. If you are using bucket milkers, be certain to rinse all milk contact surface areas completely and thoroughly until the water runs clear.
b. The hottest water temperature is needed during the hot-wash or cleaning cycle. Be sure to check that your hot water starts at around 170°F for this cycle and doesn’t fall below 120°F throughout the cleaning cycle. This is the cycle that removes butterfat, protein, and minerals. It uses slugs of hot water and chemicals to scrub the interior surfaces.
4. Acid wash: This should be used after washing equipment using hot water and detergent. This will help prevent bacterial growth over a longer period.
5. Bulk tank: The bulk tank can be a culprit for PI issues if not properly cleaned. Be sure to clean it with water at a temperature above 155°F after each milk pick-up. Check that the outlet valves, receiver jars, and components are also cleaned.
6. Milk cooling: Poor cooling of milk in a bulk tank is another avenue that will easily allow psychotropic bacteria to grow. Milk should be cooled down to 40°F within 1 hour of milking for the first milking stored in the bulk tank, and down to 36 to 38°F within the next hour. For subsequent milkings, the blend temperature should remain below 45°F and then be cooled like the first milking. Storing milk at temperatures of 33 to 35°F may not completely kill temperature-resistant bacteria, but it can significantly slow their growth. Remember that bacteria in milk can double every 15 minutes when not cooled properly.
Many factors can impact your PI counts. Bacteria will start growing almost immediately if anything is wrong with your system. Especially during this colder weather season, remember to keep a close eye on your PI counts to help you maintain your quality milk and keep your PI counts down.
If you would like more information or have questions, contact Daniela Roland, Franklin County Dairy Educator, at 717-809-2194 or dj6158@psu.edu.
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