Controlling egg dioxin levels from laying hens with outdoor run

Summary

After the first news items concerning raised dioxin levels in eggs from hens with outdoor access were published in the summer of 2001, Wageningen UR carried out intensive research activities to understand the problem and to find a way to manage the problem.
In 2004 the first Wageningen UR report on this issue was published. It described the possible factors that were associated with high egg dioxin levels in organic poultry farms. The most striking feature was the number of laying hens on the farm. Small and middle sized farms regularly produced eggs that exceeded the dioxin levels set out by the EU. In a follow-up study the relationship between egg dioxin levels and flock size was further analyzed and on-farm control measures were tested. Flock size was shown to be correlated with the use of the outdoor run. Two explanations were found for this observation. The first explanation is that large farms only open the barn doors late in the morning or even at the beginning of the afternoon. Small farms, on the other hand, often do not have doors at all or open them early in the morning. Furthermore, it turns out that the amount of time spent in the outdoor run is inversely related with the size of the flock. Hens from a large flock spend no more than 20% of the available time outside. The increasing scale of organic poultry systems thus already diminishes the problem with dioxin levels. Especially since large-scale organic poultry farms have a market share of 99% in The Netherlands. Various observations from the current project confirm the hypothesis that duration of outdoor run use is related to egg dioxin levels. On one farm with the same flock of hens, but kept under three different management systems, we found a direct relation between duration of outdoor run use and egg dioxin levels. Secondly, on farms where we decreased the amount of time that the hens were allowed outside and fed them inside the barn, egg dioxin levels dropped markedly. Thirdly, we noted a marked lowering of egg dioxin levels after hens were confined inside the barn due to a potential threat of aviary influenza infection from wild birds. When outside, hens pick up soil, worms and insects. The dioxins present in these are transferred very efficiently to the hens’ eggs. The longer the hens stay outside, the higher the intake from these sources, which results in high egg dioxin levels. Historical pollution of the soil with dioxins is the main cause of dioxin in the eggs of hens kept in outdoor runs. We found a clear correlation between dioxin levels in soil and in eggs from chickens kept on this soil. This project showed that replacing contaminated soil with fresh sand resulted in a marked drop in the egg dioxin levels. Although worms and other micro fauna could contribute to the egg dioxin levels, we still do not know what the relative contribution from these sources is as compared to the contribution from soil uptake. The knowledge that was gained with this project can now be used to efficiently control egg dioxin levels in poultry with outdoor access, by taking measures mainly directed at the duration of outdoor run use. Thanks to these measures and
the introduction of a dioxin monitoring protocol, dioxin levels can nowadays be managed quite easily. Small organic enterprises still need some attention, as they generally do not take part in the dioxin monitoring protocol, due to economic reasons. Their market share however, is less than 1%.