Biology Reference
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stressors are involved. Therefore, so far as possible, multiple indicators are
preferable. One such multiple indicator is the transcriptome, which includes
all expressed genes in the genome and thus includes all physiological
responses to the environment.
DOMESTICATION AND BEHAVIOR
Behaviors associated with fitness in a natural environment may not differ
greatly from those found in domesticated stock under relatively primitive
husbandry conditions. Thus “native fowl” in villages of Southeastern Asia
obviously cope with their environment although they may receive only mini-
mal care such as being fed unusable by-products of subsistence farming or
leftover food scraps and some protection from predators.
Those behaviors favoring domestication of a species have been described
(
Cheng, 2010; Hale, 1969
), and chickens fit the pattern well. Behaviors that
were essential in the wild may be unnecessary or even counterproductive in
terms of well-being under modern systems of husbandry. Thus, extreme
alertness and flighty behavior may lead to waste of energy and injuries in
attempting to escape from otherwise harmless stimuli when predators are
not present. Aggressiveness in obtaining desired resources may result in
low-status birds' failure to receive adequate necessities even when enough is
supplied for all. Broody behavior, essential to fitness in natural environ-
ments, is undesirable in domestic conditions and has been all but eliminated
by breeders in egg-production stocks.
GENETIC
ENVIRONMENTAL INFLUENCES
As species-specific activity, behavior is under genetic control through regu-
lating physiological homeostasis. In artificial environments, it may be diffi-
cult to know, in the absence of experimental data, whether differences
between stocks are of genetic or environmental origin or if both kinds of
influence are at work. For example, age at onset of egg laying, egg weight,
intensity of egg production, and duration of laying have been under effective
genetic selection for many generations but the stimulus of day length and
artificial control of photoperiods can also have large effects. Attempts have
been made to rule out environmental effects by standardizing environmental
conditions, as when stocks are compared for egg production in random sam-
ple tests. Even so, stocks being compared may have different requirements
for maximum performance or special characteristics which make them super-
ior in some environments and inferior in others.
The existence of genotype by environment interactions for behavioral
traits (as for production traits also) complicates the assessment of behavioral
problems and possible approaches for improving the welfare of chickens by
genetic means. Thus, if a particular egg-laying stock should possess a limited
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