The genetic standardization of industrialized animals and the preservation of their genetic diversity have both been inherent to the animal selection activities developed by humans since the Neolithic era. The tension between these two contradictory processes has increased with the creation of breeds, and has become critical with the intensification of animal breeding and its globalization over the last 50 years. With the pressure of market forces pushing the standardization process to its extreme, how can sufficient genetic variability be preserved to ensure the sustainable genetic improvement of animals? This question has become a real challenge for the international animal breeding community, which is seeking a degree of diversity despite the trend towards global standardization. Following the Michel Callon’s idea of science as a source of diversity (Callon 1994), this paper analyzes through three case studies the trajectory of scientific knowledge and its role in reconfiguration of socio-bio-technical agencements (Selmi et Joly 2014) of cattle breeding at international level. The example of the most profitable and internationalized Holstein breed is used to demonstrate tensions existing between different actors of the globalized market of genetic resources.