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 itspen 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 affecttheir pen mates’ growth through their behavior. We investigated whether pigs selectedfor a relatively positive (+SBV) or negative genetic effect (-SBV) on the growth of theirpen mates and kept in either barren or straw-enriched pens differ in fearfulness. Effectsof 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 individuallyto 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) andin the novel environment test +SBV pigs showed less locomotion than -SBV pigs afterintroduction of the bucket (P <0.05). Furthermore, straw-enriched pigs were faster thanbarren 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 theyare less fearful or more curious than pigs in barren housing. Straw-enriched pigs also hadlower salivary cortisol concentrations than barren housed pigs (P <0.001). Pigs classifiedas high-resisting in the backtest spent more time near the person in the human approachtest (P <0.10) and showed more locomotion (P <0.10) and vocalizations (P <0.001) afterintroduction of the bucket in the novel environment test than low-resisting pigs. Giltsappeared less fearful than barrows, because they were faster to touch a rope in the novelrope test (P <0.05) and faster to approach (P <0.05) and touch a person (P <0.10) in thehuman 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 bucketonce it was lowered (P <0.10) and were overall more active (P <0.01). Gilts also had lowerbasal 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 noveltytests seems to depend also on their housing conditions, coping style, and gender.