Genetic Influences on the Behavior of Chickens Associated with Welfare and Productivity - Genetics and the Behavior of Domestic Animals - page 332

were also encountered by Craig et al. (1983, 1984, 1986) , who found that
duration of tonic immobility as a criterion of fearfulness of genetic stocks
gave results that were inconsistent with those obtained when the same stocks
were compared in terms of escape and avoidance behavior. Therefore, cau-
tion is appropriate in interpretation of behaviors associated with fearfulness
as indicating welfare problems unless other kinds of evidence are also
present.
Nervousness, feather loss, and hysteria are likely to occur in some genetic
stocks, but not in others, when group size is “large” and hens have been kept
for a period of several months in barren, high-density cages ( Buijs et al.,
2009; Craig et al., 1983; Lay et al., 2011 Elmslie et al., 1966; Hansen, 1976;
Shimmura et al., 2010 ;). Minimum group size associated with hysteria in
susceptible stocks probably varies but the risk appears to rise rapidly when
more than 12 are present. Repeated and severe episodes of hysteria are asso-
ciated with reduced well-being because of resulting scratches, torn skin,
feather loss, and reduction in feed consumption and egg production ( Campo
et al., 2001; Hansen, 1976 ).
Open-Field Activity
Open-field activity has been used as a criterion of fearfulness in rodents
( Bellavite et al., 2009; Overstreet, 2012 ). The test in livestock has been
recently reviewed by Forkman et al. (2007) . Faure (1981b) selected bidirec-
tionally for differences in open-field activity of 2- and 3-day-old chicks. The
technique used was highly automated and Faure (1980) estimated that one
person could measure between 500 and 1000 chicks per day. Large and
significant differences were established between active and inactive lines
over an eight-generation study. The inactive or more fearful line had a higher
resting level of plasma corticosterone at two weeks and about twice as high
a level at five weeks when stressed, but differences were not found at 6 or
25 weeks of age ( Faure, 1981a ). Also, hens of the more fearful line con-
sumed less feed for a few days when a different kind of feeder was used.
Tonic Immobility
The phenomenon of induced tonic immobility (TI) has been known for cen-
turies and its duration in chickens is generally interpreted as an indicator of
fearfulness ( Campo et al., 2012; D ´ vila et al., 2011; Gallup, 1974a; Jongren
et al., 2010 ). That TI is influenced genetically was evident from large and
moderate realized heritability estimates obtained in single-generation selec-
tion studies, respectively, by Gallup (1974b) with 21-day-old “Production
Reds”, by Campo and Carciner (1993) , and Anderson and Jones (2012) with
White Leghorn hens. Also, Craig and Muir (1989) obtained a moderately
large heritability estimate on White Leghorn hens which had been kept in