Much attention has been made in recent years regarding the degree of variation in growth rates which occurs in individual swine which are farrowed weekly groups in modern production systems. Systems of production which produce weekly flows of animalsfrom the same genetic background find that by the time the animals are ready to market, the weight distribution from the smallest to the largest animals can often have a range of up to 100 lbs. Typically, sorters are employed to market the animals in asuniform a weight group as possible by assembling the number which fill a semi-load. The goal is typically to create an average weight which optimizes the revenue from the buying program of the slaughterhouse to which the animals are contracted or marketed. After the first load of animals is removed for marketing, the remainder is allowed to continue until sufficient animals are available at the targeted average weight to fill the semi again, which attempts to ensure the greatest total revenue for the group. Since the finishing barn is gradually being emptied by this marketing strategy, the overhead associated with the building cost in all-in, all-out systems, which may be a variable cost (as in rental charge per space per day), is allocated to the remaining animals and eventually becomes so burdensome that it results in the necessity to dump the remainder, even though the animals have not achieved ideal marketing weights. In some cases, insufficient building space is available during certain seasons of year, such as the late spring and summer months when growth slows, to achieve target weights before the building must be emptied to accommodate the next group. It is observed that producers often target the maximum revenue from the buying scheme to guide the timing of marketings, which often means measuring only sort loss as a guide to select optimal average marketing weights. Others may attempt to calculate the profit-maximizing weight as a target but typically do so on the basis on an individual animal since only the average of the average daily feed intake (ADFI) and feed efficiency (FE) is available from records upon which to conduct this estimation. We can surmise that every animal has a unique ADFI and FE, and therefore a unique profit maximizing final weight but it is impractical with current technology to measure, and since animals are not marketed individually, these average metrics are employed. Various models have been undertaken to estimate optimal marketing strategies for larger, sophisticated and complex swine production processes.
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