But that's just my thoughts. Second cutting is put up in cool weather. The regrowth is leafier with the stems being finer. Now IF the second cutting had time to mature it would get stemmier. However it barely has time to grow a foot before cool weather sets in and retards growth.
Second cutting has a lower stem to leaf ratio.
This is the fiber that goes into the cecum. That is why the reason for feeding hay is mainly to keep the gut moving and the microbes in the cecum healthy. The more important thing to look for in determining quality of hay is how it was harvested and stored. This would entail if is was dark brown in spots and moldy. We are very picky about how our hay is baled and stored.