An independent company is hired to record the amount of milk produced by each cow and to take milk samples from each cow. The milk samples are used to determine the fat and protein content of each cow's milk.

These measurements are taken eleven times per year and the recorded measurements are summed to determine how much milk each cow produces per lactation. The length of an official lactation is 305 days.

The values represented in the chart are an average of the lactations of the entire herd, expressed in both Kilograms and BCAs. BCA stands for Breed Class Average. This is a unit of measurement adopted by the Canadian dairy industry; it is used to compare individual cows to others of the same breed and in the same state of lactation.

For those who are unfamiliar with farming practises, having Breed Class Average values of 200 for each of Milk, Fat, and Potein is considered to be quite good. To have the herd average which the DeJongs have reached is a very high achievement, which requires good cows and a lot of hard work.