Abstract: The augmentation of farmers’ income constitutes a pivotal economic cornerstone for the realization of Chinese-style modernization. Utilizing micro-level survey data encompassing 475 beef cattle farming households in Yunnan Province, this study employed a Structural Equation Model (SEM) to empirically examine the mechanisms through which interpersonal relationships influence farmer’ breeding income. The empirical results demonstrated that: (1) Interpersonal relationships exerted a statistically significant and positive impact on farmers’ breeding income, with the magnitude of this effect being most pronounced in the context of close-knit relationships between farmers and their proximate agricultural counterparts. (2) Mediation analysis revealed that family farm operators, cooperative directors, breeding enterprise executives, governmental personnel and adjacent farming households all served as significant mediators in the pathway linking interpersonal relationships to breeding income, among which family farm operators exhibited the most robust mediating effect. (3) Heterogeneity analysis further delineated that the mediating role of cooperative directors was more salient within the Han ethnic cohort, whereas family farm operators played a more prominent mediating role among ethnic minority farmers. Consequently, it is imperative to construct a digitalized breeding information-sharing platform to foster cross-regional and cross-ethnic technological dissemination, refine the policy support framework to enhance the organizational architecture of the breeding industry chain, and innovate mechanisms for social capital cultivation to facilitate the establishment of diversified cooperative networks among farming households, thereby ensuring the sustainable augmentation of breeding income.