In the 1970s and 1980s Dutch farmers replaced their dual-purpose Friesian cows with Holsteins, a highly specialized American dairy breed. The changeover was related to a major turnabout in breeding practices that involved the adoption of quantitative genetics. Dutch commercial breeders had long resisted the quantitative approach to breeding that scientists had been recommending since World War II. After about 1970, however, they gave up their resistance: the art of breeding, it was said, finally became a science. In historical overviews this turnabout is seen as part of what is called the "modernization project" in Dutch agriculture that the government instigated after the war. Economic developments are assumed to have necessitated this project, and specialization of production is seen as a natural consequence. This essay argues that the idea that the art of breeding was turned into a science is to a certain extent misleading. Furthermore, it aims to show that economic pressures and government policies cannot adequately explain the turn toward Holsteins. A better understanding can be obtained by framing the Holsteinization process as the result of a changeover in breeding culture--that is, in the ensemble of shared convictions, beliefs, conventions, methods, practices, and the like that characterized practical cattle breeding and that involved scientific, technical, economic, aesthetic, normative, and commercial considerations.