Purpose: To evaluate the success of behavioural interventions designed to improve preventative animal health planning by dairy farmers in Wales. Methods: Interviews of farmers, veterinarians; focus group with extension officers; post-hoc written reflections from project managers; survey of farmers and veterinarians; farmer dropout analysis. Findings: The combination of interventions inspired by the RESET model of behavioural change helped farmers to implement new animal health planning behaviours. Crucial to the success of the project was the brokering role of extension agents and curation of AKIS relationships by project managers. This led to the establishment of symbiotic relationships which helped to deliver successful behavioural interventions. Practical implications: Illustrates the need for strong project and AKIS management to deliver combined behavioural interventions to farmers. It also demonstrates the danger of narrow evaluation methods which fail to delve deeper into the symbiotic relationships needed to deliver interventions in practice. Theoretical implications: Adds empirical evidence to an integrated behavioural change model (RESET) and explicitly connects the concepts of knowledge brokering and social capital with successful delivery of behavioural change. Originality: (1) Contributes novel empirical evidence on how to effect farmer behaviour change based on a large-scale national project. (2) explicitly highlights knowledge brokering, social capital, and good project management as crucial to delivering behavioural change projects, (3) reflects on the value of mixed method evaluations of behavioural change projects.