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relatives, in addition to that of the individual. If families are housed in kin
groups, then BLUP selection has elements of both kin and group selection.
We showed that multi-level selection in kin groups was effective in reducing
detrimental social interactions, and reduced mortality, which contributed to
improved weight gain. Simple multi-level selection using standard animal
model BLUP was easy to implement, only requiring that animals be housed
in kin groups.
GENERAL CONCLUSIONS
The wild progenitors of domesticated chickens possessed a number of traits,
including absence of highly specific environmental requirements that pre-
adapted them to domestication. They continue to show adaptability and have
responded to man's selection as seen by wide diversity among breeds and
types. Nevertheless, because of large and rapid changes in housing systems
and husbandry practices during the last 50 years, questions arise as to
whether their welfare is compromised and whether genetic adaptation has
been adequate. Criteria used in assessment of chickens' well-being include
overt indicators (bodily injury, morbidity, weight loss, non-molt feather loss,
death, and mean days survival of groups), physiological and immune
responses, productivity, and behavior. With the exception of overt indicators,
difficulties of interpretation of the various criteria lead to the conclusion
that, so far as possible, multiple indicators should be used. Nevertheless,
because behavior is the means by which animals attempt to cope with their
environments, behavioral observations can yield valuable clues as to what is
causing impaired welfare, and it is clear that behavior-related problems can
themselves have major adverse consequences.
Most behavioral differences found among domesticated stocks of chick-
ens can be shown to be determined genetically and are under polygenic
influence. However, it is often difficult to know whether those differences
arose because of foundation population differences, random genetic drift,
adaptation to local environments, or different goals under artificial selection.
The tendency to assign behavioral differences to breeds needs to be moderated
when only a single strain within a breed has been used for characterization.
Long-term selection studies for behavioral or economic traits that succeed
have shown that profound correlated responses are likely to accompany the
primary responses.
Although selection to improve behaviors associated with well-being has
been effective in most experimental studies, commercial breeders are under
economic constraints that may prevent their ready adoption of programs to
address those problems. Behaviors that are easily identified (such as broodi-
ness) or that leave traces (such as feed consumed) are more amenable to
selection than those that must be measured by time-consuming observations
(e.g., pre-lay pacing, fear-related and aggressive behavior). It has also been
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