In many cases, the second cutting of hay has fewer weeds in it. Absence of weeds, however, does not mean that the quality will necessarily be higher. Many factors go into the quality of hay, but the most important is stage of maturity of the plant. More mature plants have fully developed seed heads, thus indicating lower quality. Hay that is past optimal maturity will also have loss due to leaf shatter. If the second cutting of hay is very mature, then it will not be higher quality than the first cutting. Other factors that affect hay quality are growing conditions, plant species, weather conditions, and harvesting conditions.
For more information, you can read the following articles: Factors That Affect Hay Quality, Hays for Horses, and Hay Publications by Region.
