How is the feed intake for feed approach 2 determined, as the tool only asks for percentages?

How is the feed intake for feed approach 2 determined, as the tool only asks for percentages?

The model estimates feed intake based on gross energy requirements. This includes energy for growth, grazing, and lactation among others. The second feed approach uses the gross energy requirements to determine total feed intake based on feed items. It is important to understand that this approach is less accurate compared to feed approach 1 and may lead to an overestimation (underfeeding) or underestimation (overfeeding) of feed production-related emissions.