Genetic Influences on the Behavior of Chickens Associated with Welfare and Productivity - Genetics and the Behavior of Domestic Animals - page 327

be used that are not frustrated by the absence of nests, or within-strain selec-
tion should be directed towards selecting for quiet sitting behavior rather
than stereotyped pre-laying behavior. Mills et al. (1985) demonstrated, in a
brief selection study, that such selection could be effective.
Increased pacing before egg laying was not seen in high-density,
multiple-bird cages, as shown by Ramos and Craig (1988) . Crowding in
multiple-hen cages reduces the opportunity for increased pacing behavior.
Even so, the question arises as to whether the environment in crowded cages
differs enough from that in single cages so that results obtained in single-
bird cages are relevant. The greater “enclosure” of space which exists among
hens in a group may result in less anxiety than would be seen in an
individual-hen cage. Therefore, the question arises as to whether selection
against stereotyped pre-laying pacing, even if found to reduce stress in that
environment, would also reduce stress in multiple-hen environments.
Feather and Cannibalistic Pecking
A behavioral problem occurring especially among hens kept for table-egg
production is feather loss and cannibalism. In most production settings these
vices are greatly reduced by beak-trimming. However, behavioral and physi-
ological evidence, reviewed earlier, indicated that beak-trimming causes pain
which persists for weeks and perhaps even months. The Brambell committee
( Bramble, 1965 ) concluded with reluctance that de-beaking of birds should
be permitted for a limited time to control outbreaks of “vice” (feather peck-
ing and cannibalism). However, within a short period of time they hoped
that suitable strains would be available and in adequate supply so that
de-beaking was no longer necessary.
Craig and Muir (1993) showed that direct selection to reduce beak-
inflicted injuries could be rapid when group selection was used. They kept
intact-beak hens separately by sire families in multiple-hen cages and
selected sire families to produce succeeding generations on the basis of hen-
days without beak-inflicted injuries for 168 days from 16 to 40 weeks of
age. Selected lines achieved 75% of the possible selection differential by the
second generation.
Agonistic Behavior
Gamecock matches frequently terminate in the death of the loser. Selection
of winners in game breeds to sire progeny of future generations has without
doubt included selection for strength, agility, stamina, and other elements of
behavior necessary for that outcome. Game breeds also have accelerated
blood prothrombin and coagulation times ( Mohapatra and Siegel, 1969 ) and
arteries and veins that are stronger, smaller in diameter, and thicker walled
as compared with White Rocks ( Steeves and Siegel, 1968 ). Social dominance