In our next release, there will be a biology change that will impact every diet.
Over time, questions have been asked about the energy values (both of feeds and of recipes) predicted by CNCPS 6.1 and 6.5. The general consensus has been that they have been low. This becomes very apparent in heifers, dry cows, cow/calf, and any diet high in forage.
At the same time, CNCPS has always struggled predicting total tract NDF digestibility.
During the development of version 7, different passage rate equations and a hind gut model were integrated. These changes support the findings and consensus previously mentioned.
So, what is changing? The passage rate equation for forages will be updated using the NorCow equation. This equation predicts a much slower kp (0.5 to 4% per hr vs 2-6%). The result is that potentially digestible NDF (CHO B3) has a longer rumen residency time. Additionally, based upon simulations from CNCPS v7, the CHO B3 intestinal digestibility for all feeds will be dropped to 5% (from 20%). This 5% represents a good average across multiple diets.
Prior to the release, I will show several examples of what to expect. Overall, expect ME allowable production to INCREASE. The increase varies by animal type and diet. Check back for more details!