Effects of scalding and dehairing of pig carcasses at abattoirs on the visibility of welfare-related lesions

There is increasing interest in developing abattoir-based welfare measures for pigs.The primary aim of this study was to determine the most appropriate place on theslaughter line to conduct assessments of welfare-related lesions, namely apparentaggression-related skin lesions (hereafter referred to as 'skin lesions'), loin bruising andapparent tail biting damage. The study also lent itself to an assessment of theprevalence of these lesions, and the extent to which they were linked with productionparameters. Finishing pigs processed at two abattoirs on the Island of Ireland (n =1950 in abattoir A, and n = 1939 in abattoir B) were used. Data were collected over 6days in each abattoir in July 2014. Lesion scoring took place at two points on theslaughter line: (1) at exsanguination (Slaughter Stage 1 [SS1]), and (2) followingscalding and dehairing of carcasses (Slaughter Stage 2 [SS2]). At both points, eachcarcass was assigned a skin and tail lesion score ranging from 0 (lesion absent) to 3 or4 (severe lesions), respectively. Loin bruising was recorded as present or absent.Differences in the percentage of pigs with observable lesions of each type werecompared between SS1 and SS2 using McNemar/McNemar-Bowker tests. Theassociations between each lesion type, and both cold carcass weight andcondemnations, were examined at batch level using Pearson's correlations. Batch wasdefined as the group of animals with a particular farm identification code on a givenday. The overall percentage of pigs with a visible skin lesion (i.e. score > 0) decreasedbetween SS1 and SS2 (P<0.001). However, the percentage of pigs with a severe skinlesion increased numerically from SS1 to SS2. The percentage of pigs with a visible taillesion and with loin bruising also increased between SS1 and SS2 (P<0.001). Therewas a positive correlation between the percentage of carcasses that were partiallycondemned, and the percentage of pigs with skin lesions, tail lesions and loin bruising(P<0.05). Additionally, as the batch-level frequency of each lesion type increased,average cold carcass weight decreased (P<0.001). These findings suggest that severeskin lesions, tail lesions and loin bruising are more visible on pig carcasses after theyhave been scalded and dehaired, and that this is when abattoir-based lesion scoringshould take place. The high prevalence of all three lesion types, and the links witheconomically important production parameters, suggests more research into identifying key risk factors is warranted.