Development of a social motivation test to assess piglets’ affective state following surgical castration

English. Qualification and quantification of animal emotions are long-standing challenges; one cannot simply ask animals how they feel. Rather, sets of indirect indicators must be interpreted. In case of piglet castration, an array of indicators, including (neuro)physiological, autonomic, behavioural, and immunological recordings are available to evaluate the pain induced by the procedure. Surgical castration leads to increased cortisol concentration, modified frequency and structure of vocalizations, and impaired behaviours for days after the procedure, and is thus concluded to be painful. Potential for local anesthetics to alleviate the impact of castration is therefore extensively studied, using similar indicators. However, while most of these seem to target sensory response to the procedure, their ability to illustrate the complex emotional aspects of pain has been questioned. Recently, development of behavioural tests aiming to record proxies of piglets´ affective states after castration has been initiated, but no standard test is available. The present study involved development of such a test, focusing on piglets´ social motivation immediately after castration as measured, among others, by the latency to contact littermates. Tested piglets were individually introduced at one end of an arena (2.4 x 0.8m), facing, at the other end, three of their littermates in a heated area. Three obstacles were placed between the piglet and the littermates (height: 7 ± 2 cm). The test was concluded when the piglet reached the grid separating him from the littermates, or after 3 minutes. Video recordings were used to determine the latency to reach the grid, and tracking analysis of video sequences (LoliTrack 5) enabled quantification of the speed and distance moved. The study, performed under approval of the Danish Animal Experimentation Inspectorate and the Danish Medicines Agency, included 149 piglets between 3 and 4 days old tested in a Danish commercial farm immediately after being subjected to 1 of 3 treatments: castration without anesthesia (n=50), castration with prior administration of local anesthetic (Procamidor® Vet. 2x0.5mL) as performed by Danish farmers according the industry’s requirements (n=49), and sham handling without tissue damage (n=50). Piglets were given analgesics (Melovem® 0.1 mL) within 24h after the procedure. Eighty-nine percent of the piglets reached their peers within the time limit, with an average latency of 49 ± 38 s. Preliminary analysis of the video tracking sequences performed on 66 animals showed an average speed of 8.2 ± 3.4 cm/s. Further results will be presented.

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