Hence the practice of using antibiotics for growth stimulation could result in selection for resistance.[75][76] Antibiotics are not fully digested and processed in the animal or human gut, therefore, an estimated 40 to 90% of the antibiotics ingested are excreted in urine and/or faeces.[77][78] This means that as well as finding antibiotics in human sewage and animal manure, both can also contain antibiotic-resistant bacteria which have developed in vivo or in the environment.