Why is UDP useful to animals?

The main advantage to animals is that the Undegradable Dietary Protein or Undegradable Intake Protein (UIP) it that is a known figure while feeding. For example, if the UIP of your feed is 10%, then you need to adjust the amount of protein that you feed by that amount to compensate for it. If the UIP of the feed is unknown and you are feeding on the basis of total protein, then you would be underfeeding your animals.