Relationships among aggressiveness, fearfulness and response to humans in finisher pigs

Mixing unfamiliar pigs is common in modern production, resulting in intense aggression potentially leading to injury and stress. One solution is breeding against aggressiveness. However, in order to anticipate the consequences of such selection, we need to understand how individual aggressiveness is related to other behavior traits. Tests were used to assess three traits of importance to pig producers: interaction with humans, response to handling, and fearfulness. Test responses (human approach (HAT), handling, and novel object (NOT)) were compared with skin lesions for 257 grow-finish pigs, mixed at 10 wk of age. Skin lesions, a reliable proxy for aggressiveness, were counted pre-mixing, 24 h post-mixing, and 3 wk post-mixing. Lesions were recorded by body location (front, middle, rear). HAT was conducted at 14 wk of age in home pens by all-occurrence scans every 30 s for 9 min. Frequency and intensity (low/moderate or extreme force) of oronasal contact with observer was recorded. Activity and reactivity while entering, in, and leaving a weigh crate were recorded in the handling test (14 and 17 wk of age). NOT was conducted at 17 wk of age. Pigs were moved to an arena, given a 1 min acclimation period, then 5 min exposure to a novel object (basketball). Pigs were scored for latency to approach within 1 m, 0.5 m, and to touch the ball, and on number of times crossing the 1 m and 0.5 m lines, and touching the ball. Generalized linear mixed models compared behavior test variables and lesions. Test responses were compared using a Mantel test. Pigs with more 24 h post-mix front lesions took longer to cross the 1 m line (P = 0.049). Pigs with more 24 h post-mix rear lesions interacted intensely with observer (P = 0.026). Pigs with more 3 wk post-mix front lesions were less active in the weigh crate (P = 0.021) and took longer to touch the ball (P = 0.033). Pigs with more 3 wk post-mix middle lesions were faster to the 0.5 m line (P = 0.005), took longer to touch (P = 0.006), but touched it more (P = 0.049). There were no significant relationships between behavior tests, suggesting no consistency in responses across contexts. In conclusion, responses in HAT and NOT were related to 24 h post-mix lesions, while responses in NOT and handling test were related to 3 wk post-mix lesions suggesting that selecting for less aggressive pigs could have unintended consequences for other important behavior traits and that these relationships should be explored further.