Most farmers have been in the habit of using a bull a couple of years and then selling him to the butcher before his real worth was discovered. A bull’s ability to produce heifers that make good cows can only be definitely told after his heifers have freshened and made records. Some of the best pure bred breeders in the United States will not use a bull on their best cows until one hundred of his daughters are in the Advanced Registry which means that beginning at the age of two years they must produce 250.5 pounds of butter fat annually and must increase the production to 360 pounds of butter fat at the age of five years. In this way the best bulls are ascertained and are used to the best advantage. But there is also a way for the average farmer to receive the benefits of a good tested-out breeding stock at low cost. I refer to the co-operative bull associations and quote from Kimball’s Dairy Farmer concerning them: “A co-operative bull association is a farmer’s organization whose purpose is the joint ownership, use, and exchange of three or more high-class pure bred bulls. The territory covered by the association is divided into three or more breeding blocks and a bull is stationed in each block for the service of the fifty or sixty cows in the block. Every two years the bulls are interchanged. Thus, at a small cost, a bull for every sixty cows is provided for six or more years. The cost of bull service is greatly reduced, the best bulls obtained, and the bulls of outstanding merit are preserved for their entire period of usefulness.” CHAPTER IV. WHAT TO FEED =Chemical Analysis.= The chemical analysis of feed does not by any means tell the whole story. Wheat straw, for instance shows up very well in chemical analysis but experiments have shown that it takes more energy to digest it than it produces. Even when we figure only the digestible nutrients, the nutrients which by chemical analysis are found to be digested by animals, we do not by any means have the whole story. For instance, in human food we find that the protein in milk is about four times as valuable as the protein in the bean. In the results of a feeding experiment reported in Dr. McCollum’s “Newer Knowledge of Nutrition” on page 75, it was found that when the source of protein was the bean, four times as much was required for maintaining the body weight of the animal as when the source of protein was milk. We used to figure protein as protein and carbohydrates as carbohydrates but now we discriminate. We must learn to figure them in the results they produce. This is extremely difficult to do scientifically. When an animal must have a variety of feeds who can tell just what proportion of her production is due to certain foods eaten?