| Scope and method of study. The purpose of this study was to develop a system level optimization model based on the 1998 National Research Council (NRC) swine growth and nutrient requirement model. The optimal swine ration formulation model that directly accounted for the amount of nutrient excretion, and the required changes in waste treatment facilities was developed. Data from series of low protein and phosphorus feeding trials conducted at Oklahoma State University (Carter et al., 1999; 2000; 2001; 2003) were used to validate the simulation model. The MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) and the Minos solver in GAMS 2.5 were used for statistical and optimization analysis, respectively.; Findings and conclusions. This study revealed six important findings. First, the simulation results based on the initial NRC model suggest that profit could be increased by restricting growth and increasing the percent of carcass lean during the later finishing stage. Second, the re-estimated parameters of DE intake, protein, and phosphorus retention equations with the experimental data on corn-soybean meal diet were significantly different than the NRC values derived from farm level data. The difference tended to reflect the difference between experimental and on farm growing conditions. Third, the digestable energy and proportion of nitrogen in essential amino acids were found to have significant effects on DE intake, protein, and P retention. Including the dietary nutrient effects in growth equation estimation improves the model predictability. Fourth, the nutritional contents of the rations and the manure, lagoon size, acres required for manure application, and waste handling cost were greatly reduced in the overall profit maximizing model as opposed to the stepwise profit maximization model. Fifth, the number of animals fed had little influence on the feed rations, growth trajectory, lean percent at slaughter, as well as N, P and DM excretion when there was adequate cropland for manure application. Sixth, microbial phytase supplement was used in the optimal rations, when land available for manure applicable was limited. The results from this study can provide a guide for swine feeding operators to improve feed efficiency, and minimize the waste cost particularly when land for manure application was limiting. |
