Farm Animal Metabolism and Nutrition

Chapter 14

Rapid Metabolizable Energy Assays

J.M. McNab

Roslin Institute (Edinburgh), Roslin, Midlothian, UK

Introduction

The economic importance of energy in the
formulation of least-cost diets for poultry
and the increasing poor profitability of
commercial poultry production are sustain-
ing interest in the metabolizable energy
(ME) values of diets and constituent raw
materials. The need to formulate diets with
accurate ME values and to make judge-
ments on the effects of treatments, such as
conditioning or the addition of enzymes, is
re-emphasizing the need to have a reliable
means of deriving ME. From time to time,
it is debated whether a net energy (NE)
system might be a better basis on which to
judge the energy status of poultry diets, but
whatever system is finally adopted energy
balance experiments are almost certain to
form the means whereby both ME and NE
values are derived.
Over the past two decades, two factors
have stimulated research in energy deriva-
tions. The first was the introduction of
rapid bioassays for ME in the late 1970s
and their development during the 1980s;
the second was the adoption of energy
declarations, with the associated chemical
control equation, into the animal feed trade

in Europe in 1986. The latter event focused

particularly on the accuracy, repeatability

and suitability of different methods as a

means of measuring ME.

Not surprisingly in view of its com-

mercial relevance, the topic has been

widely reviewed. Sibbald (1979) described

the evolution of his method and later

produced a very detailed review (Sibbald,

1982); at various times, others have

assessed progress (Farrell, 1981; McNab

and Fisher, 1982; McNab, 1990). Since

1975, an enormous number of publications

have appeared on this subject; for example,

13 years ago Sibbald (1986) listed 561

references related to this area of research,

only five of which pre-dated 1975. Since

then, the pace has slowed somewhat but

without any consensus on what constitutes

the ideal procedure to derive ME.

Most recently, emphasis seems to have

fallen on repeatability of ME values, across

laboratories, across time, across ages and

across species, and of variations in dietary

ME data. The introduction of energy

declarations and of a control equation

encourages this, because it is presumed that

each system is based on a well-defined and

reproducible characteristic, namely the ME

© CAB International2000. Farm Animal Metabolism and Nutrition

(ed. J.P.F. D’Mello) 307