The nature and determination of metabolizable energy : a thesis presented for the partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
Part 1 of this thesis involves a review along quantitative lines of
investigations concerning metabolizable energy (ME) in poultry
nutrition. A model for the mechanism of nitrogen (N) excretion is
presented and examined in an experimental section comprising Part 2.
In Part 1, Chapter is an exposition of the distribution and
utilization of feed energy and raises the subject of additivity and
questions of standardization of ME assay procedure. Chapter 2 consists
of 2 sections. Section 1 provides a literature review of the bioassay
determination of apparent metabolizable energy (AME). It covers an
analysis of the nature of AME and explains basic concepts, provides
mathematical definitions and perspectives and N corrected AME values
(AMEn) are discussed. Further it describes methods of determination and
provides an examination of the factors involved in AME variation.
Section 2 deals with the nature of true metabolizable energy (TME) in
which definitions and derivations of TME are provided, the relationship
between TME and AME given, deviations from linearity of the energy
excreted (EO) on energy input (EI) regression investigated and N
corrected TME values (TMEn) discussed. Additionally, methods and
evidence bearing on the central premise to TME are presented and other
areas that have gained attention reviewed.
In Part 2, the subject of Chapter 3 is a linear experimental model
developed by King (1984) to explain deviations in linearity of the
relationship between N excreted (NO) and N intake (NI) as it may apply
to adult cockerels and the nature of the correction of TME values to
zero N balance (ZNB). Chapter 4 deals with 2 experiments, LN 202 and LN
204. The primary objective of Experiment LN 202 was to examine and
investigate the regression relationship, EO on EI obtained for adult
cockerels, and to assess the effect on it of correcting EO to ZNB.
Experiment LN 204 was set up to study the impact of diet and assay
procedure on TME of meat and bone meal (M & B) and to examine the effect
on these values of correcting to ZNB. The effect of assay procedure on
TME and TMEn of a whole diet was also explored.
In Experiment LN 202 2 slopes were obtained for the regression
relationship, EO on EI, and on correcting EO to ZNB slope
satisfactorily represented the relationship. This was consistent with
expectations arising from the model. The model suggests that this slope
contains a bias element that causes TME values to deviate from unbiassed
In Experiment LN 204 the TME values of M & B as determined by dietary
inclusion and by direct supply were compared and assessed in terms of
the model. Correction of the TMEs to ZNB resulted in a single value.
TME assessment of a whole diet by 2 different assays resulted in similar
values when the values, according to the model, estimated the same
quantity and different values when the quantities measured were, as
predicted by the model, different. Correction to ZNB caused like values
to deviate and unlike values to come closer together.
Chapter 5 provides an overview of the model and the experimental
findings and outlines the conclusions that have been drawn from this