In recent decades, animal welfare has attracted the attention of various groups for reasons including its role in achieving SDGs, community health, prevention of zoonotic diseases, and ethical issues. Stockmen have a vital role in fostering animal welfare. Given the crucial role of stockmen in ensuring animal welfare, this study attempts to assess the factors affecting the occurrence of pro-animal behavior among dairy farmers using an expanded version of Campbell's theory. In this study, a cross-sectional survey and a closed-ended questionnaire were used to collect data. Also, through a random sampling approach, 122 traditional stockmen and 208 industrial stockmen were selected in Iran. In addition, in order to assess the measurement model, test the hypothesis and provide descriptive data, Smart-PLS₃ and SPSS₂₆ software were used. The results revealed that access to livestock inputs (Beta=0.21; Sig=0.0001), anthropomorphism view (Beta=0.12; Sig=0.009), and attitude (Beta=0.53; Sig=0.0001) had positive and significant effects on pro-animal behavior. Moreover, cost (Beta=-0.14; Sig=0.004) had a negative and significant effect on pro-animal behavior. In total, independent constructs could explain 44 percent of pro-animal behavior variance. This study contributes to the development of the literature in animal welfare, social psychology and sustainability fields. In addition, it helps policymakers, scientists and related organizations to strengthen pro-animal behavior among stockmen in order to build up animal welfare.