Animal production systems have changed dramatically over the last two
decades. Knowledge of energy metabolism and environmental physio- logy
has increased as appears from many textbooks on these disciplines. The
contents of the symposia on energy metabolism of farm animals show this
and they have initially focussed on feed evaluation and later on com-
parative aspects of energy metabolism. They show part of the progress
being made. Application of knowledge of energy metabolism for animals
has a long history since Lavoisier. In addition to this, studies about
the environ- mental requirements of animals have shown that we are still
far from ac- curate assessment of these requirements in terms of
nutrients and ener- gy. I n model studies on energy metabolism
researchers have recognized the interaction between the environment and
the energy requirements of animals. Estimation of energy requirements
has been done in physiolo- gical, physical and behavioural studies. The
impact of conditions as en- countered by animals in various production
systems has been approached from different viewpoints related to these
different disciplines. In addi- tion, various kinds of infections
(bacterial, parasitic: subclinical, clini- cal) have been evaluated only
recently with regard to their effect on pro- tein and/or energy
metabolism and thus on production. People working in the field of feed
evaluation have defined how che- mical and physical properties of
nutrition infiuence energy to be derived for maintenance and production.