Feeding, more than any other single factor, determines the productivity of lactating dairy cows. Approximately 75% of the differences in milk production between cows is determined by environmental factors, with feed making up the largest portion. Feed represents about 50% of the total costs. Therefore, a good feeding is necessary for profitable milk production.

At the Cal Poly Dairy Unit, students, along with professors, work together to develop an appropriate ration mix for each of the different cows housed at the dairy unit. The daily intake for lactating cows is based on body weight and on forage quality. As a guide for estimating consumption of hay feed, the rule of thumb is about 3% of the total body weight of each cow for excellent forage quality. The Cal Poly Dairy produces a unique mix ration for the lactating cows, the dry cows (including cows that are pregnant), and the hospital pen. For calves, the dairy uses pre-mixed rations.