Abstract
BackgroundAlthough Ascaris suum is the most common pig nematode, the on-farm transmission dynamics are not well described.MethodsWe performed a 1-year field study on five organic pig farms, mapping egg contamination levels in pens and pasture soil as well as faecal egg counts in starter pigs, finisher pigs, dry and lactating sows. The uppermost bedding material was sampled from three pen areas (resting, intermediate and latrine) of shallow and deep litter pens.ResultsAscaris suum was found on all farms. Averaged across farm and season, the prevalence of A. suum was 48, 64, 28 and 15 % in starters, finishers, dry and lactating sows, respectively. For starters and finishers, the prevalence varied with season increasing towards the end of the year when 83–96 % of finishing pigs from each farm had fresh liver white spots. Farrowing pastures were contaminated with a mean of 78–171 larvated eggs/kg dry soil depending on farm, while pastures for starter pigs contained 290–5397 larvated eggs/kg dry soil. The concentration of eggs in soil was highest in the autumn. Indoors, all pen areas were contaminated with A. suum eggs at comparable levels for shallow and deep litter. Overall there were 106, 445 and 1331 eggs/g dry straw in the resting, intermediate and latrine areas, respectively. However, more eggs were undergoing development in resting areas (44 %) compared to intermediate (33 %) and latrine areas (13 %). Irrespective of area, more eggs were undergoing development in the autumn, but overall there were very few fully developed (i.e., infective) eggs in the bedding material. Laboratory embryonation of eggs from the bedding material nevertheless revealed that an overall mean of 79 % of the eggs were viable.ConclusionThe organic pigs of all ages were continuously exposed to A. suum, but mainly younger animals were infected. Deep litter appeared to be a less important source of A. suum eggs than previously believed compared to shallow litter. Long-term pasture rotation to eliminate pasture contamination was not possible, and control programs should therefore include thorough cleaning indoors and composting/long-term storage of bedding material and manure to inactivate eggs and reduce transmission to pigs.
Highlights
Ascaris suum is the most common pig nematode, the on-farm transmission dynamics are not well described
As A. suum eggs need a minimum temperature of 14.5 °C for development [12], eggs only develop on pastures during the spring and summer seasons in Northern Europe [8, 9] just as development is highest indoors during the summer months [13,14,15]
General observations Piglets were weaned in batches at 7–9 weeks of age to pastures or stables
Summary
Ascaris suum is the most common pig nematode, the on-farm transmission dynamics are not well described. A single A. suum female worm may produce close to two million eggs per day [7] and the large majority of eggs die very quickly outdoors [8, 9], the potential for environmental contamination is still very high This problem is further exacerbated by the fact that those eggs that do survive can remain viable in the environment for up to at least nine years [10, 11]. As A. suum eggs need a minimum temperature of 14.5 °C for development [12], eggs only develop on pastures during the spring and summer seasons in Northern Europe [8, 9] just as development is highest indoors during the summer months [13,14,15] This in turn is reflected in seasonal variation in worm burdens, egg excretion and liver condemnation [4, 5, 16,17,18,19]
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