Final answer:
Hay should be baled at a moisture content of 15%-20% to prevent mold and microbial degradation and maintain its nutritional value.
Step-by-step explanation:
Hay should typically be baled at a moisture content of 15%-20%. At this moisture range, the hay will be dry enough to prevent the growth of mold and bacteria but moist enough to avoid being overly brittle and losing nutritional value. When hay is baled with a moisture content that is too high, above 20%, it risks undergoing microbial degradation that can lead to heat buildup and potentially cause spontaneous combustion.
In contrast, if the hay is too dry, below 15%, it can lose leaves during the baling process, which are critical for nutritional value. Therefore, option a. 15%-20% is the correct choice for the ideal moisture percentage when baling hay.