The main emphasis of this study is on milk production functions as they relate to various levels and proportions of grain and hay in a ration restricted to these two feeds. However, certain auxiliary variables representing cow characteristics and environmental conditions are also incorporated into the production function. The auxiliary variables include: stage of lactation, milk-producing ability, temperature, age, maturity, body weight and a coefficient of inbreeding. These auxiliary variables are fixed at different levels to allow expression of milk production functions when the characteristics of cows are set at different magnitudes.

This study considers the economic optima in ration specification for dairy cows and represents a cooperative interdisciplinary effort. The estimates allow derivation of production surfaces, milk isoclines and isoquants, marginal rates of feed substitution and profit-maximizing rations for cows of different characteristics (maturity, ability, inbreeding, weight) producing under specified environmental conditions.