An equally, if not more important measure is feed "quality"; feed "quality" is the energy value of feed. It is measured by the amount of usable or metabolisable energy (ME) in a given weight of feed. In New Zealand the energy value of feed is referred to as the megajoules of metabolisable energy per kilogram of dry matter (MJME/kg DM) or M/D for short.
The higher the M/D value the better the feed. For example autumn grass, with a M/D value of 11 has a higher energy value per kg dry matter than good meadow hay with a M/D value of 8.
The higher the N content, the higher the potential N in urine and N loss to water and atmosphere.