Ascaris suum parasitism in finisher pigs: welfare and economic impacts and control options.

摘要

Incidence surveys indicate that intestinal parasitism due to Ascaris suum infestations are increasingly common due to the increase in organic, outdoor and straw bedding-based housing systems for finisher pigs. The relative impacts of a perceived 'welfare' benefit of bedding and outdoor/organic production against parasite-induced negative health and associated pain aspects have not been fully explored. The authors assembled production and abattoir records for an integrated breeder farm complex, with 4 units, each housing approximately 1,000 sows, which supplied progeny pigs at the post-weaner phase at 8 weeks-old (25 to 30 kg bodyweight average) to several separate 'grow-out' sites. The costs and benefits of interventions with either an in-feed benzimidazole (morantel) or an in-water avermectin compound were also evaluated, with appropriate controls and both A. suum-infected and non-infected grow-out sites. Negative animal welfare events, total week-by-week mortality, average daily weight gains and feed conversion data were evaluated on farms. The number of intestines infected with identifiable ascarid worms and number of livers affected with typical migrating ascarid larval lesions, known as 'milk spots', were counted at specific slaughter checks. Non-infected sites remained negative during the study. On infected sites, of 1,944 untreated pigs, 846 (0.45) had detectable ascarid infections in their small intestines, of 1,920 pigs treated with ivermectin, none had detectable ascarid infection in their small intestines and of 1,980 pigs treated with morantel, 583 (0.31) had detectable ascarid infections in their small intestines. The number of livers affected with noticeable 'milk spots' was 0.51, 0.46 or 0.51 in each group, respectively. The actual cost to the carcase processor of parasite-positive offal was calculated at Euro 1 per pig. The growth rates, feed conversions and mortality rates among pigs in each group were similar. Adult Ascaris species worms are known to cause clinical signs of abdominal pain amongst animals, irrespective of other infections or factors. It was estimated that 0.26 to 0.38 of pigs exposed to A. suum in this farm system developed negative pain and welfare impacts. It was concluded that endemic A. suum parasitism had important negative impacts on animal welfare, therapy costs and abattoir incomes.