Genetic Influences on the Behavior of Chickens Associated with Welfare and Productivity - Genetics and the Behavior of Domestic Animals - page 338

control became greater. Somewhat similar results were obtained in the sec-
ond study; with intact beaks, the selected line had significantly higher egg
production, egg mass, and survival than its control. However, with two-
thirds of the beak removed, differences in egg production, egg mass, and sur-
vival were no longer as evident. Differences in production were presumably
due to stress induced by birds with intact beaks. In comparisons between the
selected and the commercially derived stock, Craig and Muir (1991) found
that egg production was at about the same level with all three levels of beak
trimming. However, the selected stock had significantly better survival when
beaks were left intact. Craig and Muir (1991) hypothesized that kin selection
favored cooperative or at least tolerant behavior as suggested by Crow and
Kimura (1970) and concluded that selection on family means when families
are reared as family groups provides a method of improving traits in which
behavioral interactions influence overall well-being and productivity.
Muir (1996) reported that after six generations, in comparison to the
unselected control, annual per cent mortality of the selected line in multiple-
bird cages decreased from 68% in the initial generation to 8.8% in the sixth
generation. Per cent mortality in the sixth generation of the selected line in
multiple-bird cages was similar to that of the non-selected control in single-
bird cages (9.1%). Annual days' survival improved from 169 to 348 days
and rate of lay improved from 52 to 68%. Annual egg mass improved from
5.1 to 14.4 kg per bird. The dramatic improvement in livability demonstrates
that adaptability and well-being of these birds were improved by group
selection. The similar survival of the selected line in multiple-bird cages and
the control in single-bird cages suggests that beak-trimming of the selected
line would not further reduce mortalities which implies that group selection
can eliminate the need to beak-trim. An independent study by Craig and
Muir (1993) , involving different foundation stock, adds confirmatory evi-
dence; kin-selection for days survival of intact-beak hens was dramatically
increased relative to the unselected control over a two-generation study. In
the Muir (1996) study, corresponding improvements in rate of lay and egg
mass demonstrated that such changes can also be profitable.
Craig and Muir (1996) compared the selected and control lines to a com-
mercial line in generation 7. Birds were not beak-trimmed and lights during
the laying period were set to high intensity. Birds that died were replaced
with extra birds of the same line. In single-bird cages performance, as mea-
sured by eggs per hen housed, the commercial line was superior to that of
the selected line but in 12-bird cages performances were reversed. The dif-
ference in ranking was due to both an improved rate of lay and viability. In
the same study, Craig and Muir (1996) observed that feather scores did not
differ in single-bird cages among genetic stocks. However, in 12-bird cages,
the selected line had significantly better feather score than the other lines.
The lines, described by Craig and Muir (1996) , were subjected to the
stress of housing at about 17 weeks, to cold stress at 36 weeks, and to heat