1. Introduction
Ž Animal behaviour is regarded as one of the best indicators of poor welfare Broom
. and Johnson, 1993 . However, despite the potential for objective assessment of welfare,
direct observation of normal behaviour is rarely used as a welfare index. In contrast, physiological measures of welfare are routinely regarded as welfare indicators, espe-
cially the activation of the hypothalamo-pituitary–adrenal axis.
Welfare has been assessed in an indirect way by observation of abnormal behaviour. For example, behaviour patterns such as stereotypes are frequently cited as evidence of
welfare problems. But it is not known whether performance of such behaviour is a Ž
. simple response to restricted feeding Lawrence and Terlouw, 1993 , whether it is bad
for the animal, whether it is part of a coping response to environmental change, or whether it even allows the animal to experience positive welfare through self-stimulation
Ž .
of endogenous opioid secretion Cronin, 1985 . In the final analysis, it is the absence of abnormal behaviour, which seems to be used as the behavioural measure of well-being.
Preference testing is also an indirect method of assessing welfare since an animal ‘‘ votes with its feet’’ and applied ethologists record the ‘‘ vote’’ rather than the reactions
to a particular environment. Preference tests suffer from the well-documented limitation of choices only indicating relative rather than absolute preference for one environment
or the other. Although preference or avoidance of a particular environment may allow us to make inferences about that environment, the welfare of the animal making the choice
is unknown. The link between preferences and welfare may break down if the choices
Ž offered fall outside the animal’s sensory, cognitive and affective capacities Fraser and
. Matthews, 1997 . Motivational testing, where animals work to obtain access to different
Ž .
commodities Dawkins, 1990 , is also an indirect method of assessment, since the behaviour recorded is generally an operant response, such as pecking a key or lifting a
lever. A recent interesting example of the potential use of behaviour as a direct measure of
Ž .
welfare is the study of Weary and Fraser 1995 of sow responsiveness to playback of Ž
piglet distress calls. They demonstrated that sows showed a stronger response more .
vocalisations, closer approach to the speaker during playback of isolation calls of piglets than during playback of white noise. Piglet calling could therefore be a useful
measure of how well the animal is adjusting to environmental changes, especially Ž
. around weaning. Weary et al. 1996 validated this approach by further demonstrating
variation in the responsiveness of sows to ‘‘needy’’ and ‘‘un-needy’’ piglet calls. It is surprising that behavioural methods for measuring welfare have focused mainly
on indirect methods when behaviour is an animal’s first response when confronted with Ž
. Ž
. an environmental change stressor . This has been well known since Cannon 1935
identified the ‘‘fight or flight’’ response of the autonomic nervous system. Similarly, Ž
. Moberg 1985 includes behaviour in his model of pre-pathological stress and regards it
as an animal’s first line of defence against a potential stressor. Since an animal’s first response to environmental change is approach or avoidance, it
makes intuitive sense that measurement of this behaviour should be an important part of any behavioural measure or index of welfare. This has been recognised by Hemsworth et
Ž .
al. 1993 in studies of the welfare of pigs during handling, and by Vandenheede and
Ž .
Ž .
Bouissou 1993 and Boissy and Bouissou 1995 in studies of the fear responses of Ž
. sheep and cattle. Hemsworth et al. 1993 commonly found that commercial pigs were
highly fearful of humans, based on avoidance of an experimenter in a standard test. The mechanism involved appeared to be a chronic stress response, since in a number of
experiments pigs that were highly fearful of humans had a sustained elevation of free
Ž .
corticosteroid concentrations Hemsworth and Barnett, 1987 . Many other studies,
Ž .
reviewed by Hemsworth and Coleman 1998 , have also demonstrated a strong relation- ship between approachravoidance behaviour and fear.
We have attempted to extend this concept to a broader range of potentially threaten- ing or stressful stimuli and have commenced development of a standard test of
responsiveness, across a number of sensory categories, which may have the potential to discriminate between stressed and unstressed pigs. This work builds on the pioneering
Ž .
study of Broom 1986 , who tipped 200 ml of water onto the backs of lying stall-housed or group-housed sows. Group-housed pigs stood up or sat for longer periods in response
to the tactile stimulus than stalled sows. The method also extends the study by Hutson et Ž
. al. 1993 , which measured responsiveness of stalled sows to 20 different stimuli. One of
the limitations of both these studies was that sows had limited opportunities to express a full range of behavioural responses to the stimuli. In Broom’s, study the sows were lying
down before testing, and in Hutson’s study, the sows were neck-tethered in partial stalls.
We tested the responses of growing pigs to 60 stimuli from five sensory categories. Since approachravoidance is such an important part of an animal’s response to stress,
we tested animals in a test pen where this behaviour could easily be expressed by the animal and easily measured by the experimenter. Our aim was to quantify the magnitude
and variation in responsiveness to the stimuli in normal pigs prior to future selection of fewer stimuli to evaluate differences between stressed and unstressed pigs.
2. Materials and methods
Kategori