What is the main concern regarding dirt and milkstone on milker parts?

The main concern regarding dirt and milkstone on milker parts is the increased bacterial counts. When milker parts, such as pipelines and milking machines, are not adequately cleaned, residue accumulates. This residue can provide a breeding ground for bacteria, leading to contamination of the milk during the milking process. High bacterial counts in milk are particularly concerning because they can compromise milk quality, leading to spoilage and decreased safety for consumers.

While the other choices may be relevant to milking hygiene, they do not directly address the critical issue of bacterial contamination that arises from insufficient cleanliness of milker parts. Increased sediment levels might occur due to poor cleaning practices, and while this can affect milk quality, it is more directly tied to sediment rather than bacterial proliferation. Likewise, decreased production efficiency and reduced shelf life of milk can be consequences of poor cleaning and higher bacterial counts, yet the primary concern centers on the direct impact of bacteria on milk safety and quality.