Abstract Globalisation has rendered the island nation of Australia more vulnerable to infectious livestock diseases, making bio-security a key concern of government. Although farmers are at the front line of disease surveillance, little is known about this group's behaviour and motives. A study to investigate on-farm bio-security practices – and in particular how farmers decide whether to report unusual symptoms in their livestock – was conducted with sheep and cattle producers in Western Australia. This article reports on the findings of the qualitative phase of the study, which consisted of in-depth interviews with 37 farmers. The study found that farmers make reporting and bio-security decisions based on the perceived risk to their enterprise. Trust in others was found to be a key contributor to perceived risk. In support of Wynne (2006), this study found that scientific institutions linked to the government suffered from lack of trust and credibility. If farmers are hesitant to trust government sources, important animal health messages may go unheeded.