This article explores the outlines of an ‘agrarian-industrial knowledge society’ that developed from about 1895. Farmers, breeders, experts and leaders of dairy companies worked in close cooperation to increase the fat percentages in milk. The challenge was to measure these percentages on the farm, and process the information in a systematic way. Feedback mechanisms resulted in the selection of productive cows, because the fat content of milk is highly inheritable through the male as well as the female line. Data gathered from dairy companies and herd books in the Netherlands has uncovered considerable geographical differences in this process of knowledge-based growth. Focusing on Friesland, a Dutch province with a rich tradition of dairy farming, the importance of institutions is illustrated. A dairy counsellor, societies for milk measurement and cattle examination as well as price systems introduced by dairy companies advanced the biological quality of cows.