The lower cost of gain associated with the alfalfa silage ration can be attributed to the greater energy content of the alfalfa when it is harvested as silage. Because of lower leaf loss and less weathering, silage contains more protein and more total digestible nutrients on the average. However, the greater protein content does not necessarily make silage a better protein source. Effect of alfalfa quality on cost of gains in corn silage growing rations. Guide to Nutrient Requirements of Beef Cattle, provides new and updated information on the nutritive content of alfalfa.
Metabolizable protein is defined as the total quantity of protein absorbed by the intestine.
With the MP system, estimates of protein available to the animal are more accurately determined. The former, the crude protein system, assumed that all feedstuffs have equal protein degradability in the rumen. This is not the case with either alfalfa hay versus silage or with alfalfa of different maturities. The 1996 NRC indicates the percentage of degradable and undegradable protein, as well as estimates of soluble protein and non-protein nitrogen constituents. For ration formulation purposes, protein constituents are used to estimate metabolizable protein.