Biology Updates Dec 2009 Patch
Based on meetings with Cornell, the following changes have been made in the core biological model:
1. CHO B3 pool: was calculated as NDF - CHO C - NDIN. Based on historical data and discussions, the NDIN should not be included. So it is now: NDF - CHO C
2. Microbial fat digestibility changed to 80% from 95%
3. Feed fat digestibility changed to a calculated value. IN CNCPSv5, all feed fats had a default intestinal digestibility of 95%. CPMv3 introduced the fat model, of which we show predicted flows from. However, the feed digestibility numbers as calculated by CPMv3 had some questions in them by many. Thus, CNCPS6.1 just implemented variable fat digestibility feed values based upon a review of Locke et. al. They are calculated as:
Feed Fat Digestibility = (C12 x C12 digestibility + C14 x C14 digestibility + ....... + C_Other x C_Other digestibility + Feed Glycerol Content x 0.9 + Feed_Pigment x 0) / Feed Fat Content
Feeds thus have dropped to a range of 60 to 85% fat digestibility.
The result is a 2-5 lb reduction in ME allowable milk depending upon fat level and feed type.
Evaluations of the updated model were conducted by Van Amburgh. Accuracy has improved and no bias exists in model predicted performance.