Assessing animal welfare at the slaughterhouse using Animal-Based Measures in docked and undocked heavy pigs

The use of Animal-Based Measures (ABMs) for monitoring pig health and welfare at the slaughterhouse has increased lately. Among ABMs, tail and skin lesions are generally recognised as ‘iceberg’ indicators of welfare issues in pigs. The aim of this study was to evaluate these ABMs at the slaughterhouse in docked and undocked heavy pigs (~170 kg live weight). The study was carried out in an industrial abattoir located in Northern Italy between January and March 2020. A 5-point scale scoring system was used to assess tail lesions, while a 4-point scale scoring system was applied for skin lesions belonging to two regions: ‘caudal’ (hind legs and tail) and ‘cranial’ (remaining area). Presence/absence of ear lesions, vertebral abscesses and swellings at the base of the tail were also recorded. Data were collected from 108 batches coming from 71 farms and for a total of 11 908 pigs, 8 694 of which were docked and 3 214 undocked. The prevalence of tail lesions, skin lesions, ear lesions, vertebral abscesses and swelling at the base of the tail was calculated at batch level. Tail lesion scores were arranged into none (score=0), mild (score=1), moderate (score=2) and severe (score≥3). Differences between the two groups (docked vs undocked pigs) were assessed using ꭓ2 test or Fisher’s test. The strength of the pairwise association between tail lesions scores, skin lesions scores, vertebral abscesses and ear lesions was assessed using the Spearman’s correlation test. For this test, an overall tail and skin lesion score was calculated for each batch by weighting tail and skin lesion scores. Swelling at the base of the tail was not included due to low prevalence. The prevalence of tail lesions was generally higher in undocked pigs than in docked pigs (P<0.0001), while no differences were found for skin lesions. In particular, the prevalences of mild lesions (score =1, 21.7% vs 5.8%, OR: 4.6, 95% CI: 4.1 to 5.2), moderate lesions (score=2, 9.3% vs 0.5%, OR: 11.7, 95% CI: 9.1 to 15.0) and severe tail lesions (score≥3, 2.3% vs 0.4%, OR: 4.2, 95% CI: 3.9 to 8.6) were significantly higher in undocked pigs than in docked pigs (P<0.0001). A strong correlation (r=0.54, P<0.001) between skin lesion scores and ear lesions was found, while a weak correlation (r=0.37, P<0.001) between tail lesion scores and vertebral abscesses was present. In this study, a difference in the prevalence of mild, moderate and severe tail lesions between undocked and docked pigs was observed. Our findings corroborate the use of skin lesions as a good indicator of welfare issues on farm, supporting the application of schemes based on ABMs at the slaughterhouse to evaluate animal welfare in pigs.