1. Keeping Chickens without Feather Pecking (in Dutch);Bestman,2002
2. Agricultural Database Dutch National Statistic Institute (CBS)http://statline.cbs.nl/StatWeb/publication/?VW=T&DM=SLNL&PA=81517NED&D1=a&D2=a&D3=l&HD=120309–1138&HDR=G2,G1&STB=T
3. Regulation Organic Animal Husbandryhttp://www.skal.nl/LinkClick.aspx?fileticket=an0aCY%2b7kWE%3d&tabid=108&language=nl-NL
4. Monitoring of Organic Farms. More Infections as on Cage Farms (in Dutch);Fiks-van Niekerk;Pluimveehouderij,2003
5. Organic Poultry Production;Lampkin,1997