However, the environmental loading ratio (ELR) of orchard-based
field rearing system is 3.44, a little bit higher than the family-operated system 3.10, and correspondingly
the sustainable index (ESI) is lower than that of family-operated organic rearing system. Despite being
close to the concept of organic production practice with respect to rearing space for exercise and feeding
patterns, the field chicken farming system has a relative poor performance with regard to environmental
pressure and overall sustainability, which is attributable to the large amounts input of external purchased
resources, e.g. the building material, drug, feed and so on. Compared with the other two production
systems in Italy, the two systems in this study have higher economic cost and heavily rely on the nonrenewable
resource inputs.