The aim of this thesis was to identify the prevalence of the porcine respiratory disease complex (PRDC) within three pig farms in Ireland. The three farms where located in the North East of the Island of Ireland, two of the farms where located in County Cavan in the Republic of Ireland, while the third farm was located in Northern Ireland in County Tyrone. The total number of sows among the three different farms amounted to 1195 pigs. using the Respig farm audit tool developed by MSD AH I audited the three farms. The Respig farm audit is made up of three phases, firstly the general audit where the environment, housing, respiratory herd health and slaughterhouse findings are scored. The second phase of the audit is to examine the presence of any of the pathogens associated with PRDC are present on the farm. Finally the last phase involves the economic simulation of various vaccine protocols against any detected pathogens and their effect on farm profitability.