Many people still use the 2001 National Research Council (NRC) computer model to evaluate diets for dairy cattle; however, the original version will not work on new 64 bit machines. Furthermore, the original software had an error in the equation used to estimate the energy requirement of grazing cows that caused a substantial over-estimation of the requirement (approximately a doubling). The equation that calculated the passage rate for dry forage also had an error that resulted in a 10 to 15% underestimation of the rate.
The Program has been modified so that it runs on 64 bit machines and those two errors have been corrected. In addition, the window size has been modified so that it will fit better on some computers.
The new version is available to download without cost at: www.ca.uky.edu/nrsp-9/
When you get to the main screen, click on the "Modeling" button located on the lower left side. When the new screen appears, scroll down and click on Software Downloads Dairy 2001 NRC. If you scroll further down the page, you will see what changes were actually made to the software by clicking "Detail Dairy NRC (2001) Software Modifications".
You do not need to uninstall the previous version for this revised program to run.
Source: Bill Weiss, Professor and Extension Dairy Specialist, The Ohio State University