GENETIC AND ECONOMIC-ANALYSES OF SOW REPLACEMENT RATES IN THE COMMERCIAL TIER OF A HIERARCHICAL SWINE BREEDING STRUCTURE

Commercial-level sow replacement rates were investigated for a 10-yr p lanning horizon using a stochastic life-cycle swine production model. A three-tiered breeding structure was modeled for the production of ma rket hogs in a three-breed static crossing scheme. Growth and reproduc tive traits of individual pigs were simulated using genetic, environme ntal, and economic parameters. Culling was after a maximum of 1, 5, or 10 parities in commercial levels within 1- and 5-parity nucleus and 1 -, 5-, and 10-parity multiplier combinations. Yearly changes and avera ge phenotypic levels were computed for pig and sow performance and eco nomic measures. For growth traits, greater commercial level response w as for systems with higher sow replacement rates, 110 to 115% of lowes t response. Phenotypic changes in net returns ranged from $.85 to 1.01 -pig-1-yr-1. Average growth performances were highest for systems with greatest genetic trend. Highest kilograms-sow-1-year-1 finished was f or 10-parity commercial alternatives. System differences in total cost s and returns per pig resulted primarily from differences in replaceme nt costs. Removal of the gilt system from analyses often reduced range s among systems for economic measures by more than 70%. Systems with t he lowest commercial replacement rates were most profitable. Within th ese systems, those with higher genetic change had highest net returns. For high replacement rates, no more than 175% of market value could b e paid for gilts, but with lower sow replacement rates commercial unit s could justify as much as 450%.