Final answer:
The Predicted Difference for milk (PDM) is a dairy cattle breeding term indicating the expected milk production difference between a sire's daughters and the average cow. It is essential for dairy farmers like Megan who track milk production in gallons and make decisions based on economic changes in the dairy market.
Step-by-step explanation:
The Predicted Difference for milk (PDM) is a term used in animal breeding, specifically dairy cattle breeding. It refers to the expected difference in milk production between a sire's daughters and the average cow in the herd. Dairy farmers, like Megan from the given example, might use this measure to select sires whose daughters are expected to produce more milk than the average cow, thereby increasing the overall productivity of the herd. In this context, Megan measures the milk output in gallons, which is the most appropriate unit for large quantities of liquid, such as daily milk production from a dairy farm. Factors such as changes in the price of milk or cheese demand can affect the dairy market, influencing decisions about milk production and management on dairy farms.