During the early stages of growth in the Oostvaardersplassen, there was a rapid succession of open grassy vegetation to dense stands of reeds, roughs and willow trees (Salix spp.). This succession would significantly reduce the habitat for waterfowl of the Oostvaardersplassen on the long run. For maintenance of the ornithological values of this nature reserve, grazing by free ranging cattle and horses was identified as a major important management tool.
There were three main objectives for introducing large free-ranging grazers:

1. To keep the grasslands suitable for grazing by geese (Anser anser, A. albifrons);

2. To prevent shallow pools and ditches from being filled up with reed (Phragmites australis), so that they will remain suitable feeding sites for spoonbills (Platalea leucorodia) and herons (Ardea cinerea, Egretta alba);

3. And, to change a reed dominated rough growth vegetation into a more open vegetation with patches of grasses, being a suitable hunting area for birds of prey (Circus spec, Buteo spec, Falco tinnunculus).

What the landscape looks like depends on the number and the type of grazers. Each has a particular effect on the environment due to differences in food preferences and social behaviour. Each grazing species influences the vegetation development in a different way: Cattle have an integral grazing behaviour but it is fairly superficial and has only a temporary effect. Horses however, graze more on fixed spots, in an intensive and systematic way influencing the vegetation on a more local scale but intensive and with a lasting effect. The red deer particularly graze the bushes and woods of the area, slowing down the growth of the trees and brushwood. Much thought was also put into the breeds of grazers chosen to be introduced. Red deer ecologically belong to this type of ecosystem, so introducing this animal into this environment was complying with natures selection.

The cattle and horses needed further thought into the most appropriate breeds as the original primeval breed of cattle and the original Western-Europe wild horse, the Tarpan, have long since become extinct.

The Heck cattle originate from a breeding experiment conducted by the Heck brothers 70 years ago, who were trying to retrieve the primeval cattle by cross-breeding old, primitive breeds such as the Camargue, Hungarian Steppe Cattle and the Scottish Highlander. So although it is a young breed, it has primitive roots. The Konik Horse was chosen because of its direct linear derived from the Tarpan. Heck cattle and Konik horses now fill the ecological niches of primeval species that once roamed the deltas and marshland areas. In 1983 the cattle was introduced, in 1984 Konik horses were released and in 1992 the red deer were added to the developing system. The number grew to more than 2000 nowadays. The cattle, red deer and Koniks are counted each year: