Hetland and Choct (2003) consider that there is a specific need for insoluble fibre. The opportunity to consume insoluble fibre afforded to hens raised on litter explains why the weight of their gizzard is higher than in hens housed in cages. According to them, the presence of feathers in the gizzard would depend on the nature of the feed. These authors assume that feather pecking is connected to a need for fibre, since in their experiments, the hens were housed in individual cages.