To achieve energy balance and maintain a constant BW, changes in feed intake and energy
expenditure must be coordinated and tightly regulated. This may not hold true for
some poultry species intensively selected for such economically important traits as
growth and meat production. For example, the modern commercial broiler breeder does
not adequately control voluntary feed intake to meet its energy requirements and maintain
energy balance. As a consequence, feeding must be limited in these birds to avoid
overconsumption and excessive fattening during production. It is important to determine
a genetic basis to help explain this situation and to offer potential strategies for
producing more efficient poultry. This review summarizes what is currently known about
the control of feed intake and energy expenditure at the gene level in birds. Highly
integrated regulatory systems have been identified that link the control of feeding
with the sensing of energy status. How such systems function in poultry is currently
being explored. One example recently identified in chickens is the adenosine monophosphate-activated
protein kinase pathway that links energy sensing with modulation of metabolic activity
to maintain energy homeostasis at the cellular level. In the hypothalamus, this same
pathway may also play an important role in regulating feed intake and energy expenditure
commensurate with perceived whole body energy needs. Genes encoding key regulatory
factors such as hormones, neuropeptides, receptors, enzymes, and transcription factors
produce the molecular components that make up intricate and interconnected neural,
endocrine, and metabolic pathway networks linking peripheral tissues with the central
nervous system. Moreover, coordinate expression of specific gene groups can establish
functional pathways that respond to and are regulated by such factors as hormones,
nutrients, and metabolites. Thus, with a better understanding of the genetic and molecular
basis for regulating feed intake and energy expenditure in birds important progress
can be made in developing, evaluating, and managing more efficient commercial poultry
lines.