In intensive farming situations, growing animals are housed in relatively barren environments. The lack of opportunity to perform substrate-interactive and manipulative behaviour patterns may affect the expression and organization of these behaviours. However, making direct comparisons of the behaviour expressed in environments of differing physical complexity is difficult. In this experiment a relative diversity index was used to compare the behavioural repertoires of pigs housed in two different environments for a period of five months. One group of pigs (substrate-enriched) had straw, forest bark and branches added to the standard pens and the other group (substrate-impoverished) did not. The pigs were individually housed, and their behaviour was focal sampled in these pens on one day each month. It was shown that the relative diversity of manipulative behaviour shown by the pigs in the substrate-impoverished environment was lower than in the pigs in the substrate-enriched environment (p < 0.05). The relative diversity of the whole behavioural repertoire shown by the pigs in the substrate-impoverished environment also tended to be lower than that in the substrate-enriched environment (p = 0.06). It is concluded that this may be due to a difference between the two groups in motivation to interact with and manipulate objects, or a function of the manipulable quality of the substrates available to them. Alternatively, exposure to substrate-impoverished environments may interfere with the ability to express manipulative behaviour. Both situations pose a threat to the welfare of growing pigs resident in barren environments.
Haskell, M., Wemelsfelder, F., Mendl, M. T., Calvert, S., & Lawrence, A. B. (1996). The effect of substrate-enriched and substrate-impoverished housing environments on the diversity of behaviour in pigs. Behaviour, 133(9), 741-761.