CNCPS Biology Model

Cornell Net Carbohydrate and Protein System (CNCPS) was developed and licensed by Cornell University Ruminant Nutrition Modeling Group. AMTS products use the latest version of CNCPS – version 6.5. By obtaining the license to the CNCPS model, AMTS can guarantee that the model is implemented exactly as developed.  

Models like the CNCPS are mechanistic models where nutrient utilization, primarily in the rumen, is described by a series of research derived, non-linear equations. Instead of having an NEL(Net Energy of Lactation) and a RUP (Rumen Undegradable Protein) value, feeds are described by their chemical fractions and fermentation characteristics. Then these “pools” are degraded (kd(digestion rate) / (kd + kp(passage rate))) and a microbial yield is predicted. Given differences in animal types, diets, etc., the total ME (Metabolizable Energy) and MP (Metabolizable Protein) is calculated for a diet. This is then partitioned to the animal requirements (maintenance, pregnancy, milk, growth, and reserves). What this allows us to do is more accurately define the diets. In today’s economic conditions and under today’s environmental scrutiny, this increased accuracy allows us to remove ration ‘safety factors’ that, in the past, led to nutrient overfeeding and greater environmental losses.

amts re calf

Proper use of the model has been shown via research to:

  • improve cow health via
    • decreased acidosis (clinical and subclinical)
    • decreased laminitis and other foot problems
    • decreased metabolic diseases incidence
  • improve income over feed costs
  • reduce nitrogen and phosphorus excretion
  • improve animal performance (milk, meat, heifer growth, etc.)
  • improve milk components
  • place a higher farm awareness on forage quality

Where are the founders/developers of CNCPS/CPM now?

, whose origins are the Fox modeling group at Cornell, obtained a license from Cornell to utilize the CNCPS core biological model. With this license, can guarantee that the model is implemented exactly as developed.
Contributors to the CNCPS effort have been many throughout the years. While many graduate students came and went, there was a core of people that spent more than 7 years working at Cornell and other places. The following lists the major contributors and where they are now:

  • D.G. Fox, One of Founding Fathers who continued development until 2005 as leader of CNCPS Project. Retired
  • P. Van Soest, One of Founding Fathers in the areas of degradation and fiber kinetics. Retired
  • J. Russel, One of Founding Fathers responsible for the rumen sub-model. Deceased
  • C. Sniffen, One of Founding Fathers specialized in feed library, rumen biology, integration. Retired, private consultant
  • W. Chalupa, Head of CPM Project Retired, Deseased
  • R. Boston, CPM development, has now moved to a different project
  • M. Van Amburgh, CNCPS developer and contributor, currently leading model research team, Faculty member at Cornell
  • R. Grant, currently working on model research team, CPM co-chair and is President RH Miner Institute
  • K. Cotanch, model research team, RH Miner Institute
  • L. Chase, CNCPS and CPM contributor, training and support for CNCPS and CPM. Faculty member at Cornell
  • T. Overton, CNCPS and CPM contributor, training and support for CNCPS and CPM. Faculty member at Cornell
  • L. Tedeschi, CNCPS contributor, 1995-2005. Currently faculty member at Texas A&M
  • V. Durbal, CNCPS programmer at Cornell, 1997-2005 VP for Development and CDO,
  • T.P. Tylutki, CNCPS contributor and developer. 1990-2005 at Cornell. Continuing model development and training/support under versions. President and CEO
  • V. Durbal, CNCPS programmer at Cornell, 1997-2005 VP for Development and CDO,
  • C. Rasmussen, CNCPS documentation at Cornell. VP for Marketing and CFO,


6.1 Biology Changes from Previous Versions of CNCPS and CPM

We have been asked by several people doing evaluations/comparisons between CPM and 6.1 biology for some guidelines since so many of the numbers have changed. The files below will help answer some of those questions. This PDF that will provide a matrix that guides you through some of the parameters you may have questions about.

Evaluation Matrix
Moving from CPM to 6.1 biology

6.5 Biology Changes from 6.1 version of CNCPS

The changes for this version were focused on improving predictions through improved laboratory analyses and better implementation of the information provided by these analyses. The changes were primarily focused on improving the prediction of Amino Acid requirements and supply for lactating dairy cattle. Changes were also concentrated on determination of Carbohydrate pools, rates of passage, and analysis methods.

Major Changes

aNDFom: Laboratories are encouraged to run NDF samples with the use of amylase (used to break down starch), sodium sulfite (to remove residual protein), and to ash the sample (to correct for soil contamination). This analysis was the standard proposed by Sniffen, et al., 1992; laboratories had drifted from the additional steps the aNDFom analysis had required. The use of increasing larger harvest equipment, flood irrigation, and various sources of dirt contamination had resulted in inflated NDF values; in some cases, up to 10 points. A return to standardized laboratory methods for this analysis will improve intake and digestion predictions in forage based diets.

NDF Time points, uNDF, and dynamic rate calculator:Recent research has explored the relationship between undigestible NDF in rations and the animal’s intake. Drawing on the relationship between the CHO-C pool and rumen fill and the CHOB3 pool rate of digestion, VanAmburgh’s lab at Cornell was able to derive time points for degradation rates of forages and non-forage carbohydrate sources. The resulting time points at which the DNDF of forages (30, 120, 240) and non-forages (12, 72, and 120) are incorporated in a dynamic rate calculator to better proximate fiber digestion in the rumen. The final time point (aNDFom240 in forages and aNDFom120 in non-forage fiber sources) show a better relationship to the CHO-C pool than does lignin x 2.4. As commercial laboratories have begun compiling a data sets for feeds they are increasingly able to provide these numbers using NIR technology

Updating the CNCPS Feed Library: Updating the more than 800 feeds comprising the library was performed resulting in re-characterization of protein pools and changed digestion kinetics. Amino Acid profiles of the library feeds were updated to reflect a greater sample pool and improved laboratory methods. Amino Acid utilization efficiencies were also updated to reflect the work of Doepel et al. (2004) and Lapierre et al.( 2007).

The changes these updates brought to predictions is discussed in these papers:

AMTS 61 to 65 whitepaper

Input sensitivity white paper

6.5.5 Biology Changes

The passage rate equation for forages was 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.

More discussion and examples of the 6.5.5 changes can be found in this paper:

CNCPS 6.5.5 Biology Changes


Model Accuracy

We are often asked about the accuracy of the core biological model, especially when people have had good success using previous versions of the biology.
In the file below, Dr. Van Amburgh calculated stats on accuracy and some herd level experiences from CNCPS 6.1 biology. I think the data clearly speaks for itself. NOTICE: This is 6.1 biology specifically and is only available from licensed groups.  As for accuracy of earlier biological versions, it was significantly lower (while still good, it just had bias and more scatter).


Most limiting slides v6.1 biology