Consistency and influence on performance of behavioural differences in Large White and Landrace purebred pigs

Abstract

According to the theory of behavioural strategies, individual animals show clear consistency when they have to adapt to environmental changes and challenges: their responses are predictable in different situations and throughout time. The main objective of this research was to evaluate behavioural differences between pigs of Large White (LW) and Landrace (LD) breeds. A total of 119 male pigs were subjected to a tonic immobility (TI) test at 4 weeks of age and classified as TI or non-TI pigs according to their response (susceptibility to and duration of immobility). The TI has been said to reflect behavioural strategies in pigs and consisted in placing the piglet on its back with a small back on its throat. Afterwards, the pigs were subjected to four more individual tests: a novel environment test and a novel object test at 13 weeks of age and 2 human tests at 16 weeks of age. Pigs were weighed and backfat and lean depth were measured. Spearman correlations between tests were calculated. In the TI test, significant differences were found between breeds, with LW pigs presenting a higher percentage of TI than LD pigs (69.09 vs. 45.31, P < 0.05), whereas LD pigs presented a higher percentage of non-TI than LW pigs. Some of the predicted correlations between the TI test and the other behavioural tests were found. Pigs with longer TI durations made fewer attempts to escape in both human tests ( P < 0.05 and 0.01). As far as the breed factor was concerned, more predicted correlations were found in LW than in LD pigs (e.g. exploring and standing time in novel object test). With respect to productivity, TI individuals of both breeds showed higher growth rates than non-TI individuals (e.g. mean daily growth of 1168.77 g vs. 1112.14 g, P < 0.05, respectively, in LW pigs). Correlations between the TI test and the other behavioural tests suggested the existence of behavioural differences between LW and LD pigs. These probably related to differences in robustness between the two breeds, which would potentially explain the stronger correlations for LW pigs. Moreover, the relationship between behavioural differences and productive traits found in the present study suggests that individual responses should perhaps be considered in future breeding programs aimed at improving both performance and animal welfare, assuming that TI response may be linked to the capacity of adaptation.