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Sow longevity has a major effect on profi tability in commercial breeding herds15). The longer a sow remains in a herd, the greater the opportunity to recuperate the initial cost of a replacement gilt and increase lifetime net income per sow21). Some studies in the U.S.A. have reported that net income per parity or over a sow's lifetime in farrow-to-wean operations increases as the number of parity increases12, 17, 18, 22), but few studies have reported economic returns per parity or sow combined with reproductive and growth performance in farrow-to-fi nish herds. Additionally, large country-to-country variation in production values, market prices, feed cost, and other expenses means that each country, including Japan, needs to determine its own fi nancial assumptions and standards in order to assess economic returns for commercial herds. Sensitivity analysis can investigate the effect on net incomes of changes in value of one parameter while the rest of the variables in the analysis remain constant4). Feed price and the market price for growing pigs are major factors infl uencing the lifetime net income of sows. In the recent years, feed prices have increased due to escalating prices of corn5). The feed prices are directly related to the costs for marketed pigs. Furthermore, relatively small changes in market price can impact the profi tability of any investment in replacement gilts22). Feed conversion ratio7) and number * Corresponding author : Yuzo KOKETSU School of Agriculture, Meiji University Higashi-mita 1-1-1, Tama-ku, Kawasaki, Kanagawa, Japan 214-8571 Tel : +81-44-934-7826 ; Fax : +81-44-934-7902 E-mail : koket001@isc.meiji.ac.jp Original Article

Assessment of Lifetime Economic Returns of Sows by Parity of Culled Sows in Commercial Breeding Herds