Silos are special modules for animal farms, added in Bright Harvest DLC, which improve the productivity of animal farms while consuming certain resources specific to the region: grain in Old World, corn in New World. They consume 1 ton of resource each 5 minutes, so by default one grain/corn farm can support up to 5 silos.
Silos increase the productivity of animal farms by +100% and also provide extra product every 3rd cycle.
They need to be built right next to the farm building and they need their own road connection to the warehouse.
Each animal farm can have only one silo.