Behaviour of isolated piglets before and after tooth clipping, grinding or sham-grinding

Needle teeth are routinely resected on pig farms to limit lesions that intact teeth may inflict to other piglets and the sow’s udder. Two resection techniques exist: clipping with pliers and grinding with a rotating grindstone. Both techniques are potential sources of pain and stress that have been addressed in a few studies but piglets’ behaviour just before and after treatment was never observed in the absence of social influences. In total, 120 piglets from 20 litters were allocated to tooth clipping, tooth grinding, or sham grinding (2 piglets/treatment/litter). In resected groups, the tip of each needle tooth was removed using sterilised pliers or a hand-held rotative grindstone. Piglets assigned to sham grinding were handled and treated as those in the Grind group with a protective covering on the grinder head to prevent tissue damage. One day after birth, each litter was separated from the dam and placed in a heated holding trolley. Selected piglets were taken individually to a separate room to undergo tooth treatment and behavioural observations. Each piglet was placed in an observation box for 1 min to be filmed. Thereafter, tooth treatment was applied by a trained handler and the needle teeth were measured and checked for minor bleeding. The piglet was returned to the observation box and filmed again for 1 min. Once all selected piglets had been treated, the litter was returned to the dam. Behavioural observations focussed on locomotion, oral behaviours, ear position and movements, and vocalizations. For behaviours that were not always visible (e.g. ear position), the percentage of time spent exhibiting the behaviour was calculated after excluding the non-visible period. Rare behaviours were transformed into binary variables. Mean treatment duration was 53, 48 and 46 s in the Sham, Grind and Clip groups, respectively. Minor bleeding was observed directly after resection in Grind and Clip piglets (22.5 vs 97.5%). For quantitative variables, the time x treatment interaction was never significant except for exploring wood shavings. Indeed, its duration increased after treatment only in the Sham group (Pre: 18.5% vs Post: 33.7%, P<0.05) and, in the Post period, it was significantly higher in Sham than Clip piglets (33.7% vs 18.8%, P<0.05) with Grind piglets being intermediate. Regarding binary variables, champing was never observed during the Pre period but, in the Post period, it differed between Sham and Clip pigs (45 vs 80% of pigs with champing, P<0.05) with Grind pigs being intermediate (60%). Numerous variables differed significantly between the Pre and Post periods: walking, exploring walls, and ears back decreased whereas being immobile, not exploring, ears in a plane or front position, and head flick increased regardless of the treatment group (P<0.05). This experiment demonstrates a marked influence of handling on piglet behaviour regardless of the tooth treatment as well as some differences between groups after treatment showing signs of pain in clipped piglets whereas signs of pain are not clear in piglets submitted to grinding.