1. Introduction
The way vertebrates react in a stressful situation varies and largely determines their adaptive capacity. Animals will react to a stressor with a series of behavioural,
physiological and neuroendocrinological activities regulated by the brain. However, not Ž
every animal of the same species will react to a stressor in the same way Benus et al., .
1987 . In mice and rats, evidence has been found for two different ways of dealing with a
stressor. The theory is, that each individual has its own coping style, which can be either active or passive. To determine this coping style, animals are tested for behavioural
traits like aggression or nest-building behaviour, or reactions in an open field test or during tonic immobility are determined. The distribution of these traits and the results in
Ž several tests are bimodal and consistent over time McGraw and Klemm, 1973; Benus et
. al., 1991; Sluyter et al., 1995 . Most of these studies are done with SAL and LAL mice,
two genetically selected lines of wild house mice. Comparable results are found in Ž
. poultry Beuving et al., 1989; Jones and Satterlee, 1995 .
In humans, several different coping approaches are recognized. In the first theory, Ž
two coping styles were recognized, resulting in type A and type B humans Glass, .
1977 . Later, some authors defined up to 12 different coping strategies, others only three Ž
. or four Pines and Kafry, 1982; Simoni and Paterson, 1997 .
In primates, individual differences in behaviour have been found but two or more distinct coping styles have not been established. In experiments with rhesus monkeys,
results of behavioural tests are fairly consistent when the same test is done twice at the Ž
same age, but they are not consistent over time and for different situations Stevenson- .
Hinde et al., 1980 . Ž
. In pigs, different theories about coping styles exist. Hessing et al. 1993; 1994a
suggest that there are two different coping styles in pigs that can be determined in piglets by performing a backtest. In this test, the piglet is put on its back and held by the
experimenter, and the number of escape attempts is counted during 1 min. Based on two Ž
. tests, piglets can be divided into the category of High Resisters HR , with more than
Ž .
two escape attempts in each test and Low Resisters LR , with less than two escape attempts in each test. The animals that did not fit in one of those groups, namely those
with exactly two escape attempts in both tests or with varying test results, were called Ž .
Doubtful D . HR and LR pigs displayed consistent differences in behavioural, physio- logical and endocrine responses to stress situations. These responses were associated
with different stress pathologies. Moreover, differences in cell-mediated and humoral Ž
immunity were found between HR and LR pigs Hessing et al., 1994b; Schrama et al., .
Ž .
1997 . Hessing et al. 1994c also found a relation with production: animals in mixed Ž
. pens with HR and LR pigs performed better than pigs in pens with only HR or only
LR pigs. Ž
. Lawrence et al. 1991 have found that female pigs responded consistently to a series
of non-social tests, but in social tests, not all responses were consistent. Erhard and Ž
. Ž
. Mendl 1997; 1998 used a tonic immobility TI test to determine behavioural strategies
in pigs. They suggest that TI reflects an active or passive strategy. Controversial to these studies are the results of Jensen et al., stating that there are no coping styles in pigs.
Ž .
They found no relations between the backtest modified after Hessing
and other behavioural tests and the intra-test consistency was low. Using factor analysis, they did
find correlations between several behavioural traits, excluding the backtest. Three personality factors are suggested by these experiments: aggression, sociability and
Ž .
exploration Forkman et al., 1995; Jensen, 1995; Jensen et al., 1995a,b . The objectives of our studies are threefold. Firstly, we investigated if individual
characteristics of pigs, measured with the backtest, are consistent. Secondly, we determined if these individual characteristics were related to sow, boar or gender.
Thirdly, we studied the relationship between these individual characteristics and the performance of the pigs. If backtest results in pigs are related to performance, this would
mean that a selection of the best performers can be made at an early age. Also, if backtest results are heritable and related to performance, a selection in sows can be
made according to their own backtest results.
2. Materials and methods
Kategori