Interest in possibilities of forage-grain substitution in the dairy cow ration has been increased by recent agricultural developments. One development is acreage control which allows farmers to grow forage as a replacement crop for grain. Another is the continuing interest in conservation: Erosion control plans ordinarily require an increased acreage of grasses and legumes and fewer acres of grains and row crops. Both of these developments increase the supply of forages relative to grains and give rise to questions of using forage profitably. One possibility is the substitution of forage for grain in rations of ruminants. The feasibility of this adjustment depends, however, on the rate at which the various classes of feeds substitute for each other.

Recent changes in price structures, with dairy product prices depressed relative to feed and labor costs, also have caused farmers to examine substitution possibilities as a means of lowering costs and increasing profits. Then, too, yearly and geographic differentials in the costs of concentrates relative to forages and to the price of milk give rise to questions of the most profitable ration under particular economic circumstances. To what extent should the grain-forage ration be varied as the price of grain changes relative to the price of forage at particular locations? To what extent should the most profitable ration differ between grain surplus and grain deficit areas or other areas where concentrates are priced at different levels? These questions can be answered only if information is available on substitution ratios. The optimum ration, in terms of profit maximization, can be determined only by relating substitution ratios to price ratios. Finally, determining the nature of the milk production surface with its expression of feed/milk transformation ratios and feed substitution coefficients is a central problem in dairy cow nutrition.