The backtest in pigs revisited – An analysis of intra-situational behaviour

Abstract

The occurrence of different behavioural phenotypes in animals (regarding temperament and personality) has increasingly attracted the attention of scientists dealing with farm animal breeding, management and welfare. As part of the adaptation repertoire, coping behaviour describes how animals deal with challenging situations. To detect different coping strategies (active vs. passive) in domestic pigs, Hessing et al. (1993) suggested using the backtest at an early age. However, the literature contains ambiguous results and criticism of the backtest. Thus, referring to Jensen (1995), the aim of our study was to analyse the backtest in terms of intra-situational behaviour (frequency distribution, behavioural consistency, heritability) in a large sample of domestic piglets (n=3555). By using a statistical resampling analysis we wanted to verify whether the individual variation in the behaviour of the piglets in the repeated backtest indicates coping strategies or just random variation. The backtest was repeated four times between the first and fourth week of life (ages 5, 12, 19 and 26 days), and the latency, total duration and frequency of all struggling attempts were recorded. Our results show a continuous, unimodal distribution in the frequency parameter and an apparent bimodal distribution in the latency and duration parameter, that probably represents a unimodal distribution with a ‘ceiling-effect’. The intra-test consistency of the behaviour (Spearman rank correlation (rS) and repeatability (R)) was moderate (rS=0.19–0.45, p<0.001; R=0.25–0.39), indicating at least a certain degree of behavioural consistency. The resampling analysis revealed that the piglets did not show just random variation in behaviour. Moreover, the piglets did not display a general habituation to the repeated backtest. Based on a large pedigree, we calculated that the heritability of the behavioural parameters ranged from 0.17 to 0.43. In conclusion, the repeated backtest does not provide evidence for definitive coping strategies that are clearly separable. We instead found pronounced individual dispositions that are partly determined by genetics along a continuum from active to passive coping behaviour. This means that individuals show both behavioural consistency and flexibility in behaviour.