Is Sarcoptes scabiei infection in pigs a major welfare concern? A quantitative assessment of its effect in the host's nocturnal rubbing and lying behavior

The nocturnal rubbing and lying behavior of commercial fattening pigs from moderately (M) and heavily (H) Sarcoptes scabiei–infected farms was investigated. The study included 4 cohorts (2 per farm) of 11-15 acaricide-treated (uninfected) and untreated (infected) 4- to 7-month-old pigs, and the time and number of behavioral bouts were monitored for 350 hours over 101 days. Auricular mites, dermatitis, and plasma histamine concentration were investigated postmortem at the age of 7 months, and histamine concentration was also analyzed at the age of 3 months in 3 cohorts. The percentage of pigs with mites was 27% and 79% in untreated farm M and H cohorts and 0% in treated pigs. Erythematous hypersensitive dermatitis was observed in both treated and untreated animals; however, histamine levels were much greater in untreated compared with treated pigs and increased with time in the former group. Rubbing was significantly increased in untreated compared with treated pigs, but it was generally low and with small variations over time. The mean rubbing time per 210 minutes (1 day sample) was 0.00-0.79 and 0.00-0.65 minutes in untreated pigs in farms M and H, respectively, and 0.00-0.15 and 0.00-0.03 minutes in treated pigs in farms M and H, respectively. The mean lying time and number of events of standing up were similar for treated and untreated pigs, and differences between farm cohorts were not associated to S. scabiei infection. Moreover, the average pig's lifelong weight gain also appeared to be independent of infection. The small effect of S. scabiei on pig behavior and growth contrasts with the much greater effect that the nonburrowing mite Psoroptes ovis has been reported to have in a comparable study in sheep ( Berriatua et al., 2001). The reasons for this outcome are unclear and could be related to differences between studies in the time when behavior was monitored in relation to initial infection, with pigs investigated at a later stage compared to sheep. Study results question the parasite's effect on pig welfare and have important implications in swine management. Moreover, differences in histamine levels in treated and untreated pigs could be diagnostically useful to detect infected herds.