Measuring food values for dairy cows

Abstract does not appear. First page follows. The Evaluation of Feeds Feed accounts for over half the total cost involved in animal production (Hopkins, 1940).6 Obviously, then, it is important to evaluate feeds correctly. Replacement Equivalent.—The problem can be best introduced by a simple example: If a dairy farmer can secure corn for $38 a ton or wheat for $37 a ton, which is the better buy? To answer this question the farmer must know how much wheat will replace in his ration a ton of corn so that the result—milk yield and change of body substance in the cows—will remain the same. In this paper the figure that indicates how much of one feed is necessary to replace a certain amount of another feed is called replacement equivalent. Since, as a rule, a ration consists of several feeds, the farmer is especially interested in knowing the replacement equivalent of feeds when they form only a part of a ration. If, for example, a daily ration includes 10 pounds of hay, 1 pound of beet pulp, 1 pound of cottonseed meal, and 3 pounds of corn, how much wheat would be required to replace these 3 pounds of corn so that the new ration with wheat has the same food effect as the old ration with corn? In this case, as usually in food evaluation, only a part of the ration is replaced; and we therefore speak here of partial replacement equivalents. Data Available at Present.—Replacement equivalents can be derived from the standard tables on total digestible nutrients: digestible protein plus digestible carbohydrates plus (2.25 × digestible fat). As (Morrison (1936)) shows, corn contains 83.7 pounds of total digestible nutrients per 100 pounds, and wheat 83.6. This is 94.6 pounds of total digestible nutrients per 100 pounds of dry matter for corn, 93.8 for wheat. Assuming that the offered corn and wheat, in the example cited in the preceding paragraph, have the same moisture content, the wheat is a slightly better buy: it contains 99 per cent of the total digestible nutrients of corn, and it costs only 3738×100=97 per cent of the price of corn.