AHOL (Animal Health Ontology for Livestock) is an ontology of characteristics defining health issues of livestock in their environment (EOL) linked to their phenotypes (ATOL). AHOL aims to provide a reference ontology of health traits of farm animals for the international scientific and educational communities, farmers, etc.; deliver this reference ontology in a language which can be used by computers in order to support database management, semantic analysis and modeling; represent traits as generic as possible for livestock vertebrates; make the AHOL ontology as operational as possible and closely related to measurement techniques; structure the ontology in relation to animal production