Divergent selection for residual feed intake alters pig behavioral reactivity to novel stimuli tests

Abstract Text: Improving feed efficiency is essential for increasing sustainable production and producer profitability. It is also necessary to ensure that feed efficiency modifications do not negatively impact animal welfare, as concerns have been raised on how genetic selection for feed efficiency impacts livestock ability to cope with stress. Therefore, our objective was to determine if divergent selection for residual feed intake (RFI) altered pig behavioral reactivity toward novel stimuli. In experiment 1, 40 low-RFI (more feed efficient) and 40 high-RFI (less feed efficient) 8^th generation Yorkshire RFI selection line barrows (107±9 days old) were evaluated. Experiment 2 evaluated 40 low-RFI and 40 high-RFI 9^th generation barrows and gilts (101±9 days old). All pigs were individually tested using both human approach (HAT) and novel object (NOT) tests. Pigs were tested for 10 min within a 4.9 x 2.4 m test arena, consisting of 4 zones. Behavior was evaluated using live and video observations, with the hypothesis that behaviorally reactive pigs would display more frequent oral, nasal, and/or facial contact with the human or object (traffic cone), zone entrances, head movements, urination, defecation, escape attempt (rearing on hind legs), and freezing (≥3 sec of no body movement) behaviors. Data were analyzed using the Glimmix procedure of SAS. In experiment 1, low-RFI barrows entered fewer zones (P<0.0001), had fewer head movements (P≤0.02), defecated less frequently (P≤0.03), displayed a shorter duration of freezing (P=0.05), and froze less frequently (P<0.0001) compared to high-RFI barrows during HAT and NOT. During HAT, low-RFI barrows also attempted to escape less frequently (P=0.001) compared to high-RFI barrows. In contrast, low-RFI barrows took longer to first contact the novel stimuli in HAT and NOT compared to the high-RFI barrows (P≤0.04). In experiment 2, low-RFI pigs contacted the novel stimuli in HAT and NOT less frequently compared to high-RFI pigs (P≤0.03). During NOT, low-RFI pigs attempted to escape less frequently (P=0.0002) and spent less time attempting to escape (P=0.04), but changed head orientation more frequently compared to high-RFI pigs (P=0.001). During NOT, barrows froze more frequently (P=0.0007) and spent longer freezing (P=0.05). During HAT, barrows entered fewer zones (P<0.0001), changed head orientation less frequently (P=0.002), froze less frequently (P=0.02), and spent more time contacting the human compared to gilts (P=0.03). These results suggest that selection for low-RFI pigs resulted in lower behavioral reactivity.

Keywords: Behavior, Feed efficiency, Pig