Genetic Influences on the Behavior of Chickens Associated with Welfare and Productivity - Genetics and the Behavior of Domestic Animals - page 320

Assessment of chronic pain by behavioral criteria appears to be a valuable
technique. For example, behavioral evidence suggested that pain and height-
ened beak sensitivity persist for several weeks or even months following
beak trimming in hens trimmed at 5 weeks of age or older ( Breward and
Gentle, 1985; Craig and Lee, 1990; Duncan et al., 1989; Gentle, 1986b, 1989,
1992; Gentle et al., 1990, 1991; Lee and Craig, 1990, 1991; Mench and
Duncan, 1998 ). Nevertheless, interpretations of behavioral evidence can be
controversial. Thus, Eskeland (1981) observed that beak-trimmed hens spent
more time “resting” and concluded that fearful running by hens of low social
rank was almost eliminated by beak trimming. However, Gentle (1986a) sug-
gested that the significant increase in resting behavior among trimmed-beak
birds was similar to the inactivity following injury seen in both human beings
and animals ( Cheng, 2005; Wall, 1979 ). Because of interpretation difficulties,
it is valuable to supplement behavioral observations with other types of evi-
dence as was done by Breward and Gentle (1985) and Gentle (1986a, 1989) .
They presented evidence that following partial beak amputation, growth of
neuromas occurred in the part of the beak remaining and that spontaneous fir-
ing of afferent neurons associated with pain occurred up to at least 12 weeks
after beaks were trimmed.
Several researchers, including Dawkins (1983) and Faure (1986) , have
used the willingness of hens to express preferences or “work” for environ-
mental conditions allowing the expression of certain behaviors as evidence
of the relative desirability of alternative environments from the hen's view-
point. Nevertheless, possible confounding factors must be avoided or com-
pensated for in such tests because previous experience with an environment
may have a powerful effect on motivation to choose or work for it so that
birds with different experiences choose differently ( Byholm and Kekkonen,
2008; Campos et al., 2008; Cornil and Ball, 2010; Mumme et al., 2006;
Petherick, et al., 1990 ).
Behaviors seen as indicating problems with the environment, such as
vacuum activities and stereotypies, are frequently cited as indicators that
the environment impairs welfare in animals ( Mason et al., 2007; Martins
et al., 2012 ). However, Hughes (1980) , Dantzer (1993) , and Mason and
Latham (2004) argue that the occurrence of such activities may allow

animals to cope.

General
Difficulties of interpretation of the various criteria of welfare have been dis-
cussed ( Clark et al., 1997; Consortium, 1988; Craig and Adams, 1984; Craig
and Swanson, 1994; Dawkins, 1998; Hetts, 1991; Hill, 1983; Hurnik, 1990;
Izzo et al., 2011; Kumar et al., 2012; Mench, 1992; Muir and Craig, 1996 ),
and there is a tendency to agree that, except for overt indicators, no single
measure has previously been shown to be adequate, at least when long-term