Genetic Influences on the Behavior of Chickens Associated with Welfare and Productivity - Genetics and the Behavior of Domestic Animals - page 323

agonistic traits was reversed relative to the control stock between adoles-
cence and full maturity.
Social inertia can confound accurate determinations of relative social
dominance ability after peck orders have become well established ( Guhl,
1968 ). Lee and Craig (1981a) demonstrated this using the same stocks
compared in the Craig et al. (1975) study. They found that the selected
strain had social dominance over the control at 5 months (before egg laying),
but the selected stock dominance ability had diminished or disappeared
when strangers of the strains were placed together at 17 months of age.
Nevertheless, selected strain pullets maintained undiminished dominance
over control pullets for the entire laying year when they were kept together
from time of housing at 5 months.
Comparisons among breeds, in which a single stock within each breed
was used, have revealed behavioral differences of genetic origin. Such differ-
ences were found for chicks' open-field activity ( Faure, 1979 ), presence or
absence of hysteria among hens in large-group-size cages ( Elmslie et al.,
1966 ), duration of tonic immobility ( Campo and Alverez, 1991; Campo
et al., 2007; Gallup et al., 1976; Jones and Faure, 1981 ), and pre-laying
behavior of individually caged hens ( Mills and Wood-Gush, 1985 ), and
eating ( Howie et al., 2011 ). Such studies are of value in demonstrating
whether genetic stock differences exist at all but could be misleading in
terms of identifying breeds as having particular characteristics. For example,
large strain differences have been shown within the White Leghorn breed for
behavioral traits. Thus, Hansen (1976) found hysteria-susceptible and
hysteria-resistant strains. Al-Rawi et al. (1976) and Buitenhuis et al. (2009)
detected differences in frequency of agonistic acts; and hens of different
stocks were found to differ in feather-loss and mortality from cannibalism
when their beaks were left intact ( Craig and Lee, 1990 ).
INBREEDING DEPRESSION AND RANDOM GENETIC DRIFT
Expected general consequences of inbreeding within a population are: there
will be subdivision into distinctive lines or subpopulations (because of ran-
dom genetic drift), uniformity will increase within subpopulations, and there
will be a general loss of vigor. Although there are widespread observations
over species confirming the consequences of inbreeding in general, the evi-
dence for behavioral traits in chickens is sparse.
A study by Craig and Baruth (1965) examined the effects of inbreeding
on vigor as indicated by social dominance ability of cockerels and pullets.
Because of small numbers available within each of five partially inbred lines,
differences among lines and uniformity within lines were not examined.
However, mean performance over the lines when compared with that of a
sample of the non-inbred and unselected population from which the lines
were derived provided the evidence needed. Partially inbred cockerels were