Responses to novel situations of female and castrated male pigs with divergent social breeding values and different backtest classifications in barren and straw-enriched housing

The growth of a pig is not only affected by its own genes, but also by the genes of its pen mates. This indirect effect on a pig's growth is represented as social breeding value (SBV) in a newly developed breeding model. It has been hypothesized that pigs could affect their pen mates' growth through their behavior. We investigated whether pigs selected for a relatively positive (+SBV) or negative genetic effect (-SBV) on the growth of their pen mates and kept in either barren or straw-enriched pens differ in fearfulness. Effects of coping style, as assessed in a backtest, and gender were also investigated. Pigs (n = 480) were subjected to a group-wise novel rope test and human approach test and individually to a novel environment test in which after 5 min a bucket was lowered from the ceiling. In the novel rope test +SBV pigs were faster than SBV pigs to touch a rope (P<0.01) and in the novel environment test +SBV pigs showed less locomotion than SBV pigs after introduction of the bucket (P<0.05). Furthermore, straw-enriched pigs were faster than barren housed pigs to touch a rope in the novel rope test (P<0.10) and faster to approach (P<0.05) and touch a person (P<0.05) in the human approach test, suggesting that they are less fearful or more curious than pigs in barren housing. Straw-enriched pigs also had lower salivary cortisol concentrations than barren housed pigs (P<0.001). Pigs classified as high-resisting in the backtest spent more time near the person in the human approach test (P<0.10) and showed more locomotion (P<0.10) and vocalizations (P<0.001) after introduction of the bucket in the novel environment test than low-resisting pigs. Gilts appeared less fearful than barrows, because they were faster to touch a rope in the novel rope test (P<0.05) and faster to approach (P<0.05) and touch a person (P<0.10) in the human approach test. In addition, in the novel environment test, gilts were more calm (P<0.05) in the period before the bucket was introduced, paid more attention to the bucket once it was lowered (P<0.10) and were overall more active (P<0.01). Gilts also had lower basal cortisol concentrations than barrows (P<0.001). Overall, these results suggest that +SBV pigs might be less fearful than SBV pigs. Furthermore, the response of pigs in novelty tests seems to depend also on their housing conditions, coping style, and gender. (C) 2013 Elsevier B.V. All rights reserved.