The apparent prevalence of skin lesions suspected to be human-inflicted in Danish finishing pigs at slaughter

Skin lesions on pigs inflicted by humans compromise animal welfare and are the subject of increased public and political attention in Denmark. Systematic surveillance of such skin lesions was enforced in April 2010 at all Danish pig abattoirs, through the recording of meat inspection Code 904 for the presence of skin lesions suspected to be human inflicted. The objectives of the present study were to (a) estimate the apparent prevalence of Code 904s at the pig and herd owner level; (b) characterise the distribution of deliveries with pigs demonstrating a Code 904; (c) characterise the distribution of herd owners with repeated Code 904 recordings; and (d) determine the developments in Code 904 prevalence over time in Danish finishing pigs in the period from May 1, 2010 to September 30, 2013.Data from the 12 largest finishing pig abattoirs from Denmark were included and recordings were comprised from 65,504,021 pigs from 651,681 deliveries originating from 10,796 herd owners.Overall, 7200 (0.011%) of the pigs were recorded with a Code 904, and 21% of herd owners had a minimum of one Code 904 delivery with at least one pig with skin lesions inflicted by humans. On the pig-level, the apparent prevalence was 0.020% in 2010, which was reduced to 0.008% in 2013. In the first quarter of the study period, 17% of the herd owners had a Code 904 delivery, while 7% had one in the last quarter. Nine per cent of the herds had more than one Code 904 recording, with up to 16 Code 904 deliveries from one herd owner. Most deliveries included one single pig with a Code 904, but up to 102 Code 904 recordings were made in a single delivery. The apparent prevalence at the four smallest and four middle sized abattoirs decreased from the first to the second quarter, while the apparent prevalence decreased more substantially in the largest four abattoirs; with significant decreases from both the first to the second, and from the second to the third quarter.The study showed that recorded skin lesions suspected to be inflicted by humans are prevalent, but the apparent prevalence decreased from 2010 to 2012 and 2013. The development in Code 904 over time could be due to a real decrease or be due to other factors such as changes in the way the lesions were recorded, while both underestimation and overestimation appeared to be present.