The majority of dairy calves around the world are dehorned with methods that cause them pain and distress. In some dairy production systems, extensionists may influence dehorning practices used on farm through their advisory and knowledge-transfer role. The aims of this study were to investigate Brazilian extensionists' knowledge, beliefs, and behavior regarding dehorning dairy calves. As little research has addressed this question, a qualitative, theory-building approach was used and the theory of planned behavior was used as a conceptual framework to guide data collection and analysis. In-depth, semi-structured interviews were undertaken with 15 extensionists working in Santa Catarina, Brazil, to examine their role in the adoption and rejection of pain-mitigation strategies at dehorning. The interview transcripts were free coded, identifying 9 major themes within and across interviews. Transcribed interview responses were then coded to constructs in the theory of planned behavior. The themes and constructs that emerged through analysis of the interview responses were combined to develop a conceptual model of extensionists' beliefs, attitudes, and behavior toward recommending protocols for dehorning aimed at minimizing pain. The extensionists interviewed believed that it was necessary to dehorn all dairy replacement heifers. Despite being aware of methods to minimize pain during and after dehorning, all of the interviewees recommended or used the hot cautery method, with no pain control. This method was described as the most effective, cheapest, safest, and fastest method of dehorning. The majority (12) of interviewees rejected the caustic paste method, citing negative past experiences or unfamiliarity with the method and the belief that the method is less practical and riskier for farmers. More than half of the interviewees did not recognize dehorning as painful or expressed the belief that the pain associated with the procedure did not justify the use of pain control. Although a small number of extensionists (4) recognized potential sources of social pressure to change, including the rejection of pain-inflicting practices by some farmers, the Brazilian general public, and animal-protection societies, they did not identify these factors as a reason to change their existing practices. Interviewees expressed the belief that the adoption of practices to minimize pain and stress, such as dehorning very young calves, using caustic paste and pain control, would increase labor and costs associated with dehorning. Extensionists' negative attitudes toward recommending practices that minimize pain during and after dehorning appear to be embedded in the production-focused political and economic agriculture environment and a lack of education, research, and legislation regarding farm animal welfare. © 2013 American Dairy Science Association.