Farm policies for the feeding of livestock.

The animal feeds industry has known for some 25 years how to formulate a compound diet which conforms to a set of minimum or maximum nutrient constraints, and to ensure that the ingredients are chosen in such a way as to minimize the cost per ton of the resulting compound. The computer technique of lincar programming has been in use for over 10 years by the larger firms as a routine step in diet formulation, and it is accepted practice in England that minimum or maximum percentages of the more important nutrients are printed on the bag. However, as Dent & Casey (1967) remind us, animals do not eat percentages, but measurable weights of nutrients per day; and the total weight of the feed in which these nutrients are carried may be of secondary importance. Limits on voluntary intake will certainly impose extra constraints on the formulation of a ration but these will be by no means as rigid as the specification of fixed nutrient percentages. Formulation of a ration in terms of daily requirement for calories, amino acids, vitamins and minerals is no more complex a problem than that which faces the commercial compounder. A linear programme can be used to devise both daily rations and percentage diets.