The amount of protein a cow needs will depend very much on her size, growth, milk production and state of pregnancy. Milk production is the biggest influence on protein needs. Crude protein needs based on milk production is shown below. Crude protein is measured as the sum of degradable protein plus undegradable dietary protein.
Milk Production vs crude protein requirements (%):
Early lactation: 16 - 18%
Mid lactation: 14 - 16%
Late lactation: 12 - 14%
Dry: 10 - 12%
Please remember that requirements for rumen degradable protein and undegradable protein are only "guesstimates".
In order to get an accurate requirement, the protein requirements of the rumen microbes and of the cow needs to be considered.
The microbial protein made available also needs to be included in the calculation.
Any lack of protein can be made from all protein sources.
However, not all microbial protein or undegradable dietary protein eaten will be available to the cows.
Factors sucha s digestibility of amino acids or feed intake will affect the type and amount of protein used by cows.
Hence, rumen degradable protein and undegradable dietary protein requirements can be calculated estimates.