In conclusion, all of the test variables were related to one another. Open-arm avoidance represented the purest measure of fear of novelty, whereas entries into closed arms and number of
lines crossed in the OF were the purest measures of activity. The EPM appeared to provide the best way to separate the fear of novelty and activity-related elements, indicating that the EPM may
be a useful behavioural model of fear of novelty or avoidance in pigs. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Fear of novelty; Pig, Fearful behaviour; Tonic immobility; Elevated plus-maze; Lightrdark test; Open-field
1. Introduction
Fear is an undesirable emotional state that reduces welfare, growth and reproductive Ž
performance in farm animals Hemsworth and Barnett, 1991; Hemsworth et al., 1989; .
Ž .
Jones, 1989; Mills and Faure, 1990; Seabrook, 1990; . According to Boissy 1995 , fear and anxiety can be defined as ‘‘emotional states that are induced by the perception of
Ž .
Ž .
any actual danger fear state or potential danger anxiety that threatens the well-being of the individual’’. In commercial farms, pigs are frequently exposed to aversive
conditions including different stock, people and changes in their physical and social Ž
environments. Specific examples are mixing with unfamiliar conspecifics e.g., Jensen, .
Ž 1994; Jensen and Yngvesson, 1998 , inconsistent handling procedures Hemsworth
. Ž
et al., 1987 , and exposure to a new environment Mormede et al., 1984; Beattie et al.,
`
. 1995; Erhard and Mendl, 1999 . In most situations, animals have conflicting motivations
to avoid and investigate novel stimuli, and the balance is strongly dependent on the Ž
. magnitude of novelty Gray, 1987 .
Models of the approach–avoidance conflict have been useful for developing be- Ž
. havioural tests of fear in rodents see Gray, 1987 , but there are few standard and
Ž well-validated experimental methods for studying aversion to novelty in pigs Erhard
. Ž
. Ž
. and Mendl, 1999 . The elevated plus-maze EPM and the lightrdark LrD test are the
Ž most commonly used behavioural models of fear in rodents Cole and Rodgers, 1995;
. Hendrie et al., 1997; Janczak et al., 1999; Lister, 1987; Pellow et al., 1985 . In the
Ž .
former, an anxiolytic anxiety reducing effect is indicated by an increase in the percent Ž
of entries into open arms and the percent of time spent on open arms Lister, 1987; .
Pellow et al., 1985 , whereas in the latter, it is the increase in the percent of activity and Ž
time spent in the aversive, brightly lit compartment Costall et al., 1987, 1989; Onaivi .
and Martin, 1989 . Performance in EPM is found to be predictive of behaviour in other Ž
. models of anxiety for rodents Trullas and Skolnick, 1993 , and new experimental work
Ž .
suggests that this model may be used to measure anxiety in pigs Andersen et al., 1999 . Anxiolytic agents, such as diazepam, are found to reduce the avoidance of open arms in
Ž .
the EPM both in rodents and pigs Andersen et al., 1999; Cole and Rodgers, 1995 , but an anxiolytic effect of diazepam in the LrD test has only been reported in rodents
Ž .
Ž .
Costall et al., 1989 . The open-field OF test was originally developed for laboratory Ž
. animals Gray, 1987; Hall, 1936; Whimbey and Denenberg, 1967 , but has later been
Ž used to assess fear responses in domestic species pigs: Beattie et al., 1995; von Borell
. and Ladewig, 1992; foxes: Bakken, 1994; cattle: Boissy and Bouissou, 1995 . In the OF
test, it is the conflict between exploration of and aversion to an open area, which Ž
. determines the behaviour Asano, 1986; Crusio et al., 1989 . The usual interpretation of
the OF data in rodents has been that a high defecation rate and low activity indicate a Ž
. high level of fear or emotionality Broadhurst, 1957; Denenberg, 1964 . Other results on
rodents, however, have shown that measures of defecation and locomotion in the OF loads on two different and independent components, which represent emotionality and
Ž .
activity, respectively Ramos et al., 1997; Whimbey and Denenberg, 1967 . Ž
. Ž .
The tonic immobility TI , motor inhibition response has been used to a great extent Ž
as an index of fearfulness in poultry Heiblum et al., 1998; Jones et al., 1997; Scott and .
Moran, 1993 . This is an involuntary, reflexive response to fear-inducing stimuli present Ž
. Ž
. Ž
. in birds Heiblum et al., 1998 , toads Lupo et al., 1991 , rabbits Aloisi et al., 1995 ,
Ž .
Ž .
rodents Bigal et al., 1994; Tikal, 1991a,b and humans Galliano et al., 1993 , and is Ž
. sometimes referred to as a state of ‘‘pretended death’’ Tikal, 1991b . A longer duration
of TI in rats appears to be typical for individuals tending to react with anxiety and Ž
. submission in other situations Tikal, 1991b , whereas in pigs, the duration of this
Ž response is thought to reflect an active or passive coping strategy Erhard and Mendl,
. 1999 .
Before applying these different experimental models to pigs, there is a need to evaluate the methods. This can be provided by using recognised anxiolytic drugs to
Ž .
detect fear-related behavioural elements Andersen et al., 1999 , and by examining the relationship between behaviours in different tests. The aim of the present study was to
investigate the relationship between fear responses in different experimental tests of novelty in weaned pigs.
2. Materials and methods
