The table shows the differences between meat and various vegetable foods. In the basic analysis of composition both are primarily water - DM% means the percentage dry matter when the water is removed. Of what remains, the bulk in the grass is carbohydrate with only a small proportion of protein, on the other hand in the meat once the water is removed the bulk is protein. This mix of nutrients once the water has been removed is referred to as Dry matter.
It isn’t always immediately obvious from what people write whether a figure of 20% protein means 20% of the fresh material is protein as in meat or 20% of the dry matter is protein as in various grasses (especially the leguminous type such as lucerne).
The ultimate measure for comparison and for information is to report in terms of dry matter, the body simply eliminates the excess water and deals with the nutrients, it is these which need to be expressed. Values from Paul & Southgate (McCance & Widdowson’s ) The Composition of Foods are generally expressed as fresh weight, whereas many more scientific publications use dry weight.
The majority of animals eat to satisfy an energy demand, because they have evolved with specific food sources, in general this automatically comes close to supplying their requirements for protein, essential amino acids, vitamins and minerals etc. Supplying a higher fat level than is ‘normal’ changes the relationship between protein and energy.
Protein can only be used for growth up to the limit imposed by the availability of the various essential amino acids, after this it is broken down and nitrogenous waste products must be eliminated. An important concept to grasp is that of the "limiting amino acid", this is the amino acid which is lowest in the diet and due to its inavailability the other amino acid building-blocks cannot be used. To obtain sufficient amounts of the limiting amino acid the bird is forced to overeat and then eliminate the excess nitrogen. Taking excessive amounts of protein will ultimately lead to problems. The protein above that which can be used is broken down as energy ultimately and results in obesity and can lead to gout due to excretion of the excess nitrogen in urates.