Mycoplasma (M.) hyopneumoniae is the causative agent of porcine enzootic pneumonia (EP). This disease, leading to reduced weight gain, reduced feed conversion and increasing use of antibiotics, is one of the major health problems in the pig production throughout Europe. The epidemiology of EP is influenced by several factors including management, hygiene, virulence of the M. hyopneumoniae strain and other factors. In order to increase the epidemiological understanding of EP, five different studies supervised/performed by Dr. Heiko Nathues were conducted during the last five years at the Field Station for Epidemiology, Univ. Vet. Med. Hannover, Germany. The studies addressed the influence of (a) environment, (b) strain variation, (c) time of infection, (d) occurrence of infections among suckling pigs and (e) prevalence among breeding pigs. Initial results from descriptive data analysis have already been published.The objectives of the proposed project are 1) to improve the understanding of EP epidemiology by analyzing existing data collected by projects of Dr. Nathues using a multivariable approach, and2) to develop a compartmental model of the within herd transmission of M. hyopneumoniae which will allow assessing the impact of different husbandry system and potential control measures.As a result of the project, the impact of targeted intervention measures can be assessed, resulting in prevention of clinical disease, reduction of pain and suffering of animals, and in refraining from the use of antibiotics. The expected outcome is a considerable increase of the animals' health and welfare as well as a considerable reduction of the use of antimicrobial drugs in pig production.