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Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)

Abstract

A previous bulletin reported results from an experiment designed to predict substitution rates and economic optima in corn/soybean oilmeal rations for growing and fattening hogs in drylot.2 Principles and analytical models were included which illustrate that the least-cost ration depends both on (1) the marginal rate of substitution between feeds and (2) the ratio of feed prices. These basic concepts will not be repeated in this bulletin.

Since more hogs are farrowed in spring than in fall, the research reported in this study was conducted for growing and fattening hogs raised on pasture. Like the drylot study, the objectives of the pasture experiment were to estimate: (1) the production function, (2) the substitution rate between corn and soybean oilmeal at different points on the production surface, (3) the least-cost ration for different soybean oilmeal/corn price ratios, (4) the relationship between the rate of hog gains and the input of corn and soybean oilmeal and (5) the proportion of the years in which a least-cost feeding system results in greater profits than a least-time feeding system. Substitution between major classes of feed such as corn and soybean oilmeal is possible mainly where the rations are fortified with appropriate quantities of trace minerals (as well as antibiotics in the case of drylot feeding). These fortifying elements have been included in the rations of this study.

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