Lesions found at routine meat inspection on finishing pigs are associated with production system.

Pigs raised under free-range conditions are expected to experience a higher level of animal welfare than conventionally raised pigs. However, free-range conditions may challenge prevention and treatment of diseases. In order to identify disease problems associated with raising conditions, this study compared slaughter lesions in pigs from conventional indoor, conventional free-range and organic free-range production systems. The study used data from 1,096,756 pigs slaughtered at one Danish abattoir from 1 January 2013 to 31 December 2015. Associations between production system and lesions at slaughter were tested in statistical models taking year, season and herd of origin into account. Both conventional free-range and organic free-range production systems were associated with increased population averaged odd ratios (ORPA) for several lesions compared with conventional indoor systems. Pigs raised in conventional free-range and organic free-range production systems had higher odds for white liver-spots (ORPA, 5-7), tail lesions (ORPA, 3-4), arthritis (ORPA, 3), skin lesions (ORPA, 3), bone fractures (ORPA, 2), septicaemia (ORPA, 1.1-1.5) and abscesses (ORPA, 1.1-1.3) at slaughter. Pairwise comparisons of the two free-range production systems did not reveal statistically significant differences (P>0.05). In all three production systems, airway infection was the most prevalent disease complex. In contrast to previous studies, this study did not find any association between airway infection and type of production (P>0.05). Three lesions (leg swellings (ORPA, 0.4-0.5), hernia (ORPA, 0.7-0.8) and hoof abscess (ORPA, 0.7-0.9)) had lower ORs in conventional free-range and organic free-range production compared with conventional indoor production. There was a marked herd effect (intraclass correlation coefficients 21-35%) on the occurrence of white liver-spots, tail lesions, skin lesions and airway infections. These results suggest possibilities for herd-level management interventions of the problems studied.