Application of an attention bias test after surgical castration in piglets

Surgical castration of male piglets is a routine procedure performed to improve meat quality. Prior studies have shown that pain due to castration can last for up to 4 days, negatively impacting animal welfare, however the impact on affect, such as anxiety, is unclear. The objective of this study was to test the application of a novel attention bias test to assess anxiety in piglets that underwent surgical castration with or without practical pain alleviation methods. Piglets were surgically castrated (n = 22), castrated with analgesics (n = 21), or sham-handled (n = 22) at 3 days of age. An attention bias test was performed in week 1 (n = 32, 10–11/treatment) and 12 (n = 29, 9–10/treatment) to assess anxiety (an affective state), with feed (positive stimulus), loud bangs, and flashing lights (negative stimuli) presented simultaneously. Latency to visit the feeder, behavioral responses, and activity were recorded during the test. Additional data on piglets’ activity, tails, and grimaces were collected at three timepoints, at 1, 6, and 24 h after castration to determine pain experience. Piglets’ increased activity (P = 0.065), the fact that fewer piglets visited the feeder (P = 0.029), and tended to have longer latencies to visit the feeder (P = 0.092) in the attention bias test in week 1 might suggest that pain caused by surgical castration increased anxiety. No differences were detected in week 12. Castration treatment and sampling timepoint impacted activity levels hours after treatments, however, other measures were not impacted. These results suggest that more research is needed to determine how affect is impacted by pain caused by surgical castration. Activity and behavioral results somewhat support previous findings that surgical castration causes pain in piglets. As this is the first study assessing the relationship between painful procedures and piglet anxiety, more research is needed to determine a valid method to understand the impacts of these procedures on pig affect.