Overview

On pages 43 through 85 of Nutrient Requirements of Dairy Cattle Seventh Revised Edition, 2001 is a discussion of protein and amino acids. On page 74 under the title of "Predicting Passage to the Small Intestine" is a summary of two published methods of predicting AA flow to the duodenum. The purpose of the summary is to preface the subcommittee's selection of an approach to developing an AA flow sub-model for use in the NRC 2001 Dairy Model.

"In contrast to the described factorial methods (CNCPS and Rulquin) in which both the structure and the parameters were determined on theoretical grounds, the multivariate regression or semi-factorial approach allows for some of the parameters to be determined by regression. This allows the model (i.e., equations) to adapt to the measured data, and allows for at least partial correction of the errors of the mechanistically determined variables. The result is that semi-mechanistic models generally are better at predicting (forecasting) than full mechanistic models. Because of the potential for increased accuracy of prediction, and because the approach eliminated the need to assign AA values to ruminally synthesized microbial protein and endogenous protein (AA values had to be assigned only to feedstuffs), the semi-mechanistic method was the method of choice by the subcommittee for predicting the content of EAA in total EAA of duodenal protein. This approach required the development of an equation for each of the EAA and one for predicting flows of total EAA." (Nutrient Requirements of Dairy Cattle Seventh Revised Edition, 2001 pg 75)

The paragraphs that follow describe the process undertaken to arrive at prediction equations presented on pages 78 and 79. In this process, Tryptophan was dropped because of insufficient experimental data, "Only one experiment reported flows of Trp; thus, no equations could be developed for predicting the content of Trp in total EAA of duodenal protein." (pg 75)

The equation for each modeled amino acid utilizes statistically derived constants to determine the content of the AA in duodenal EAA. These values are at the heart of the AA sub-model. Because future reviews may produce constants for Tryptophan or possible revision of existing values, the equation constants have been implemented in Formulate2 as a user editable file. This approach allows for immediate implementation of any new values.

You can access the DDEAA Equation Constants from either the ration or feed record forms by clicking on the Other menu and selecting and clicking on the Maintenance & Registration menu option.

From the Maintenance Utilities form, click on the System menu and select and click on the DDEAA Equation Constants menu option.

To edit an item, left click on the item to highlight it, then click on the Edit button. When the edit is completed, click on the Save button to save the edit then click on Exit Edit to return to the list. If you decide not to save the edit simply click on the Exit Edit button without clicking on the Save button.