Sibling social context shapes responses to tail docking with rubber rings in weaned twin lambs

Tail docking with rubber rings is a routine husbandry procedure in lambs that induces pain and stress, and these effects may be modulated by social context. In lambs, the effects of sibling presence have been confounded by factors such as maternal contact or environmental enrichment. The aim of this study was to compare behavioral and physiological responses to tail docking with rubber rings in weaned twin lambs housed with either their docked or undocked sibling, or with familiar docked or undocked lambs. Forty-two 4-month-old lambs were tail docked with rubber rings and pair-housed with: (1) undocked sibling (UND-SI, n = 10); (2) docked sibling (DOC-SI, n = 10); (3) undocked familiar lamb (UND-FL, n = 11); or (4) docked familiar lamb (DOC-FL, n = 11). Behaviors were continuously recorded for 27 min surrounding the procedure (10 min before and 17 min after). Heart rate, rectal temperature, and eye surface temperature were measured immediately before and 40 min after the procedure. The percentage of change of each physiological variable was calculated relative to its baseline value. Lambs housed with undocked siblings reduced both tail-wagging events (UND-FL vs UND-SI: P = 0.004) and agonistic behaviors (UND-FL vs UND-SI: P = 0.003). In contrast, those housed with docked siblings increased both tail-wagging events (DOC-FL vs DOC-SI: P = 0.0001) and the percentage of change in eye surface temperature (DOC-FL vs DOC-SI: P = 0.002). In conclusion, housing tail-docked lambs with UND-SI attenuated behavioral indicators of pain, including tail-wagging and agonistic behaviors, whereas co-housing with DOC-SI intensified both tail-wagging and the change in eye surface temperature.